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cond-mat/9210001
|
Universal criterion for the breakup of invariant tori in dissipative
systems
|
The transition from quasiperiodicity to chaos is studied in a two-dimensional
dissipative map with the inverse golden mean rotation number. On the basis of a
decimation scheme, it is argued that the (minimal) slope of the critical
iterated circle map is proportional to the effective Jacobian determinant.
Approaching the zero-Jacobian-determinant limit, the factor of proportion
becomes a universal constant. Numerical investigation on the dissipative
standard map suggests that this universal number could become observable in
experiments. The decimation technique introduced in this paper is readily
applicable also to the discrete quasiperiodic Schrodinger equation.
| 1992-10-01
| 2009-10-22
|
[
"cond-mat"
] |
Jukka A. Ketoja
|
cond-mat/9209034
|
Temperature Correlations of Quantum Spins
|
We consider isotropic XY model in the transverse magnetic field on the one
dimensional lattice. Another name of the model in Heisenberg XXO model of spin
1/2.We solved long standing problem of evaluation of temperature correlations.
We first represent correlation function in the model, by means of completely
integrable differential equation. This is famous Ablowitz-Ladik lattice
Nonlinear Schrodinger equation.Correlation function is the $\tau $ function of
this differential equation. We solved this equation and evaluate asymptotics.
| 1992-09-30
| 2007-05-23
|
[
"cond-mat"
] |
Alexandr Its, Anatloij Izergin, Vladimr Korepin, Nikita Slavnov
|
cond-mat/9209033
|
Theory of adsorbate induced surface reconstruction on W(100)
|
We report results of a theoretical study on an adsorbate induced surface
reconstruction. Hydrogen adsorption on a W(100) surface causes a switching
transition in the symmetry of the displacements of the W atoms within the
ordered c(2x2) phase. This transition is modeled by an effective Hamiltonian,
where the hydrogen degrees of freedom are integrated out. Based on extensive
Monte Carlo renormalisation group calculations we show that the switching
transition is of second order at high temperatures and of first order at low
temperatures. This behavior is qualitatively explained in terms of an XY model
where there is an interplay between four and eight fold anisotropy fields. We
also compare the calculated phase diagrams with a simple mean field theory.
| 1992-09-28
| 2009-10-22
|
[
"cond-mat"
] |
Kari Kankaala, Tapio Ala-Nissila, See-Chen Ying
|
cond-mat/9209032
|
Surface reentrance in the semi-infinite spin-1 Ising models
|
The critical behavior of the semi-infinite Blume-Capel and
Blume-Emery-Griffiths models is investigated in the pair approximation of the
Cluster Variation Method. Equations for bulk and surface order parameters and
n.n. correlation functions are given, from which analytical expressions for the
second order bulk and surface critical temperatures are derived. The phase
diagrams of the Blume-Capel model are classified, and the existence of a
surface first order transition is discussed. This transition is shown to be,
under certain conditions, slightly reentrant, and the behavior of the surface
order parameters and correlation functions is given for such a case. The
extension of our results to the Blume-Emery-Griffiths model is briefly
discussed.
| 1992-09-28
| 2009-10-22
|
[
"cond-mat"
] |
Carla Buzano and Alessandro Pelizzola
|
cond-mat/9209031
|
Fluxes, Laplacians and Kasteleyn's Theorem
|
The following problem, which stems from the ``flux phase'' problem in
condensed matter physics, is analyzed and extended here: One is given a planar
graph (or lattice) with prescribed vertices, edges and a weight $\vert
t_{xy}\vert$ on each edge $(x,y)$. The flux phase problem (which we partially
solve) is to find the real phase function on the edges, $\theta(x,y)$, so that
the matrix $T:=\{\vert t_{xy}\vert {\rm exp}[i\theta(x,y)]\}$ minimizes the sum
of the negative eigenvalues of $-T$. One extension of this problem which is
also partially solved is the analogous question for the Falicov-Kimball model.
There one replaces the matrix $-T$ by $-T+V$, where $V$ is a diagonal matrix
representing a potential. Another extension of this problem, which we solve
completely for planar, bipartite graphs, is to maximize $\vert {\rm det}\ T
\vert$. Our analysis of this determinant problem is closely connected with
Kasteleyn's 1961 theorem (for arbitrary planar graphs) and, indeed, yields an
alternate, and we believe more transparent proof of it. {}.
| 1992-09-25
| 2007-05-23
|
[
"cond-mat"
] |
Elliott Lieb and Michael Loss
|
cond-mat/9209030
|
An alternative approach for the dynamics of polarons in one dimension
|
We developed a new method based on functional integration to treat the
dynamics of polarons in one-dimensional systems. We treat the acoustical and
the optical case in an unified manner, showing their differences and
similarities. The mobility and diffusion coefficients are calculated in the
Markovian approximation in the strong coupling limit.
| 1992-09-23
| 2009-10-22
|
[
"cond-mat"
] |
A.H.Castro Neto and A.O.Caldeira
|
cond-mat/9209029
|
Polaron excitations in fullerenes: Theory as pi-conjugated systems
|
We review the recent theoretical treatment of fullerenes as pi-conjugated
systems. Polaronic properties due to the Jahn-Teller type effects are mainly
discussed. (1) A Su-Schrieffer-Heeger type electron-phonon model is applied to
fullerenes: C_60 and C_70, and is solved with the adiabatic approximation to
phonons. When the system (C_60 or C_70) is doped with one or two electrons (or
holes), the additional charges accumulate along almost an equatorial line of
the molecule. The dimerization becomes the weakest along the same line. Two
energy levels, the occupied state and the empty state, intrude largely in the
gap. The intrusion is larger in C_70 than in C_60. These are ``polarons'' in
doped fullerenes. It is also found that C_60 and C_70 are related mutually with
respect to electronical structures as well as lattice geometries. (2) We apply
the model to the fullerene epoxide C_60O. It has the polaron-type lattice
distortion around the oxygen, and also shows the energy level intrusion in the
gap. (3) Optical properties of C_60 are calculated and discussed. In the
absorption of the doped molecule, a new peak structure is present owing to the
polaronic distortion. In the luminescence of the neutral C_60, the spacing
between H_g(8)-phonon side-band peaks and the relative intensities agree well
with experiments. In the dispersion of the third harmonic generation, the
magnitudes of |chi^(3)| agree with those of experiments at the resonance of the
lowest allowed transition as well as in the region away from the resonance.
| 1992-09-20
| 2008-11-26
|
[
"cond-mat"
] |
Kikuo Harigaya, (Fundamental Physics Section, Physical Science
Division, Electrotechnical Laboratory, Umezono 1-1-4, Tsukuba, Ibaraki 305,
Japan)
|
cond-mat/9209028
|
Photoinduced charge separation in Q1D heterojunction materials: Evidence
for electron-hole pair separation in mixed-halide $MX$ solids
|
Resonance Raman experiments on doped and photoexcited single crystals of
mixed-halide $MX$ complexes ($M$=Pt; $X$=Cl,Br) clearly indicate charge
separation: electron polarons preferentially locate on PtBr segments while hole
polarons are trapped within PtCl segments. This polaron selectivity,
potentially very useful for device applications, is demonstrated theoretically
using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard
model. Strong hybridization of the PtCl and PtBr electronic bands is the
driving force for separation.
| 1992-09-19
| 2009-10-22
|
[
"cond-mat"
] |
L.A. Worl, S.C. Huckett, B.I. Swanson, A. Saxena, A.R. Bishop, J.
Tinka Gammel
|
cond-mat/9209027
|
Electron-Phonon Driven Spin Frustration in Multi-Band Hubbard Models: MX
Chains and Oxide Superconductors
|
We discuss the consequences of both electron-phonon and electron-electron
couplings in 1D and 2D multi-band (Peierls-Hubbard) models. After briefly
discussing various analytic limits, we focus on (Hartree-Fock and exact)
numerical studies in the intermediate regime for both couplings, where unusual
spin-Peierls as well as long-period, frustrated ground states are found. Doping
into such phases or near the phase boundaries can lead to further interesting
phenomena such as separation of spin and charge, a dopant-induced phase
transition of the global (parent) phase, or real-space (``bipolaronic'')
pairing. We discuss possible experimentally observable consequences of this
rich phase diagram for halogen-bridged, transition metal, linear chain
complexes (MX chains) in 1D and the oxide superconductors in 2D.
| 1992-09-19
| 2007-05-23
|
[
"cond-mat"
] |
J. Tinka Gammel, K. Yonemitsu A. Saxena, A.R. Bishop, and H. R\"oder
|
cond-mat/9209026
|
Extracting Infinite System Properties from Finite Size Clusters: `Phase
Randomization/Boundary Condition Averaging'
|
When electron-electron correlations are important, it is often necessary to
use exact numerical methods, such as Lanczos diagonalization, to study the full
many-body Hamiltonian. Unfortunately, such exact diagonalization methods are
restricted to small system sizes. We show that if the Hubbard $U$ term is
replaced by a ``periodic Hubbard" term, the full many body Hamiltonian may be
numerically exactly solved, even for very large systems (even $>$100 sites),
though only for low fillings. However, for half-filled systems and large $U$
this approach is not only no longer exact, it no longer improves extrapolation
to larger systems. We discuss how generalized ``randomized variable averaging''
(RVA) or ``phase randomization'' schemes can be reliably employed to improve
extrapolation to large system sizes in this regime. This general approach can
be combined with any many-body method and is thus of broad interest and
applicability.
| 1992-09-19
| 2012-08-27
|
[
"cond-mat"
] |
J. Tinka Gammel, D.K. Campbell, and E.Y. Loh, Jr
|
cond-mat/9209025
|
Relaxed Excited State Geometries in a Peierls-Hubbard Model for Polyenes
|
Using parameter values relevant to polyacetylene and its finite polyene
analogs, we determine, via exact finite size diagonalization of a 1D
Peierls-Hubbard model, the relaxed geometry and optical absorption spectra of
several states of interest in optical experiments (the singlet ($1^1A_g$) and
triplet ($1^3B_u$) ground states, the singlet one ($n^1B_u$) and two ($2^1A_g$)
photon gaps, and the triplet one ($n^3A_g$) photon gap) in order to examine the
question of how well this simple model can really capture the behavior of this
simple material.
| 1992-09-18
| 2007-05-23
|
[
"cond-mat"
] |
J. Tinka Gammel and D.K. Campbell
|
cond-mat/9209024
|
Discrete to Continuous-Time Crossover due to Anisotropy in
Diffusion-Limited Two-Particle Annihilation Reactions
|
Diffusion-limited reaction A+A->inert with anisotropic hopping on the d=1
lattice, is solved exactly for a simultaneous updating, discrete time-step
dynamics. Diffusion-dominated processes slow down as the anisotropy increases.
For large times or large anisotropy, one can invoke the appropriate continuum
limits. In these limits the effects of the anisotropy on variation of particle
density can be absorbed in time rescaling. However, in other regimes, when the
discreteness of the time steps is nonnegligible, the anisotropy effects are
nontrivial, although they are always quite small numerically.
| 1992-09-18
| 2014-10-13
|
[
"cond-mat"
] |
Vladimir Privman
|
cond-mat/9209023
|
Multicritical Points And Reentrant Phenomenon In The BEG Model
|
The Blume - Emery - Griffiths model is investigated by use of the cluster
variation method in the pair approximation. We determine the regions of the
phase space where reentrant phenomenon takes place. Two regions are found,
depending on the sign of the reduced quadrupole - quadrupole coupling strength
$\xi$. For negative $\xi$ we find Para-Ferro-Para and Ferro-Para-Ferro-Para
transition sequences; for positive $\xi$, a Para$_-$-Ferro-Para$_+$ sequence.
Order parameters, correlation functions and specific heat are given in some
typical cases. By-products of this work are the equations for the critical and
tricritical lines.
| 1992-09-18
| 2009-10-22
|
[
"cond-mat"
] |
Carla Buzano and Alessandro Pelizzola
|
cond-mat/9209022
|
Generalized Coherent States for Dynamical Superalgebras
|
Coherent states for a general Lie superalgebra are defined following the
method originally proposed by Perelomov. Algebraic and geometrical properties
of the systems of states thus obtained are examined, with particular attention
to the possibility of defining a K\"ahler structure over the states
supermanifold and to the connection between this supermanifold and the
coadjoint orbits of the dynamical supergroup. The theory is then applied to
some compact forms of contragradient Lie superalgebras.
| 1992-09-18
| 2007-05-23
|
[
"cond-mat"
] |
Alessandro Pelizzola and Corrado Topi
|
cond-mat/9209021
|
Growth Model of Au Films on Ru(001)
|
In an attempt to find generic features on the fractal growth of Au films
deposited on Ru(001), a simple simulation model based on irreversible
diffusion-limited aggregation (DLA) is discussed. Highly irregular
two-dimensional dentritic islands of Au particles that gradually grow on a
larger host lattice of Ru particles and have fractal dimension d_{f}~ 1.70
each, are generated via a multiple had-hoc version of the DLA algorithm for
single aggregates. Annealing effects on the islands morphology are reproduced
assuming different sticking probabilities at nearest-neighbour lattice sites of
Au films on Ru(001). Using simulation data, islands growth are described in
analogy to diffusion-limited, precipitate growth with soft impingement of
precipities. This leads to analyse thin film island growth kinetics in such
fractal systems and to predict a main peak in scattering intensity patterns due
to interisland interference. ----------------
Copies upon request to: canessae@itsictp.bitnet
| 1992-09-17
| 2009-10-22
|
[
"cond-mat"
] |
E. Canessa and A. Calmetta
|
cond-mat/9209020
|
Non-Linear I-V Characteristics of Double Schottky Barriers and
Polycrystalline Semiconductors
|
An attempt to determine theoretically the highly non-linear current-voltage
(I-V) characteristics of polycrystalline semiconductors, such as ZnO-based
varistors, is made from the electrical properties of individual grain
boundaries under dc bias. The role played by the fluctuations of double
Schottky barrier heights at grain interfaces on driving electrical breakdown
phenomena of macroscopic samples is pointed out in terms of a binary mixture
model. An alternative trial form for the double Schottky barrier height is
introduced to reproduce the breakdown voltage as well as the high non-linear
coefficient alpha, where I propto V^{alpha}. -------------
Copies upon request to: canessae@itsictp.bitnet
| 1992-09-17
| 2009-10-22
|
[
"cond-mat"
] |
E. Canessa and V.L. Nguyen
|
cond-mat/9209018
|
Fermi-linearization scheme for itinerant electrons with Clifford
variables
|
We propose here an alternative interpretation of the fermi-linarization
approach to interacting electron systems, based on the requirement that the
coefficients of the linearized operators are Clifford-like variables, whose
anticommutator equals an unknown constant $c$. We apply the approximation to
the Falicov-Kimball model, explicitly solving the self-consistency equation for
the unknown, which turns out to behave as an order parameter. We discuss its
relation with a metal-insulator transition and some thermodynamical quantities.
In particular we show that our approximation in the $T=0$ limit reproduces
exactly the Gutzwiller results for the Hubbard model.
| 1992-09-16
| 2009-10-22
|
[
"cond-mat"
] |
Arianna Montorsi and Alessandro Pelizzola
|
cond-mat/9209019
|
Kinetic Roughening in Surfaces of Crystals Growing on Disordered
Substrates
|
Substrate disorder effects on the scaling properties of growing crystalline
surfaces in solidification or epitaxial deposition processes are investigated.
Within the harmonic approach there is a phase transition into a low-temperature
(low-noise) superrough phase with a continuously varying dynamic exponent z>2
and a non-linear response. In the presence of the KPZ nonlinearity the disorder
causes the lattice efects to decay on large scales with an intermediate
crossover behavior. The mobility of the rough surface hes a complex dependence
on the temperature and the other physical parameters.
| 1992-09-16
| 2016-08-31
|
[
"cond-mat",
"hep-th"
] |
Yan-Chr Tsai and Yonathan Shapir
|
cond-mat/9209017
|
Numerical Study of the Wheatley-Hsu-Anderson Interlayer Tunneling
mechanism of High $T_c$ Superconductivity
|
We present results obtained (by exact diagonalization) for the problem of two
t-J planes with an interlayer coupling $t_\perp$. Our results for small hole
concentrations show that in-plane superconducting correlations are enhanced by
$t_\perp$. When the constraint on double occupancy in the t-J model is relaxed,
the enhancement disappears. These results illustrate the inter--layer tunneling
mechanism for superconductivity.
| 1992-09-16
| 2009-10-22
|
[
"cond-mat"
] |
M. Arjunwadkar, G. Baskaran, R. Basu and V. N. Muthukumar
|
cond-mat/9209014
|
Metal Adatom Induced Corrugation of Cu(001)
|
We report the discovery of a metal adatom induced corrugation of Cu(001) as
probed by atom beam scattering (ABS). At Pb or Bi coverages of 0.05 (fraction
of Cu layer), and while a (1$\times$1) LEED pattern is still observed, the ABS
diffraction pattern from \underbar{uncovered} Cu(001) areas has changed
considerably from that of clean Cu(001). We show that these uncovered areas
have become up to ten times more corrugated than the clean Cu(001). We
performed several carefully designed experiments to test whether our data could
be interpreted as a result of scattering from adsorbate islands or from a
lattice of randomly occupied sites. Instead, we ascribe the nature of this
metal adatom induced corrugation to the redistribution of the Cu(001) surface
charge density due to the adsorption of Pb or Bi atoms. No effect is seen
following adsorption of weakly chemisorbed adatoms, such as Hg. A model
consistent with all our observations is presented.
| 1992-09-14
| 2009-10-22
|
[
"cond-mat"
] |
Wei Li and Gianfranco Vidali
|
cond-mat/9209016
|
Models for Monolayers Adsorbed on a Square Substrate
|
Motivated by recent experimental studies of Hg and Pb monolayers on Cu(001)
we introduce a zero temperature model of a monolayer adsorbed on a square
substrate. Lennard-Jones potentials are used to describe the interaction
between pairs of adlayer-adlayer and adlayer-substrate atoms. We study a
special case in which the monolayer atoms form a perfect square structure and
the lattice constant, position and orientation with respect to the substrate
can vary to minimize the energy. We introduce a rule based on the Farey tree
construction to generate systematically the most energetically favored phases
and use it to calculate the phase diagram in this model.
| 1992-09-14
| 2009-10-22
|
[
"cond-mat"
] |
Ofer Biham, L.-W. Chen and Gianfranco Vidali
|
cond-mat/9209015
|
Growth of Metastable High-Order Commensurate Overlayers of Pb on Cu(001)
|
We studied the growth and ordering of a Pb layer deposited on Cu(001) at 150
K. Contrary to the case of adsorption of Pb at room temperature, islands
readily form. These islands order in a high-order commensurate structure of
symmetry ( sqrt(61) x sqrt(61) ) R arctan(5/6). We followed the growth of these
islands using atom beam scattering. From the measurement of the island
diffraction peak profiles we found a power growth law for the mean island- size
versus coverage. Upon increasing the coverage another high-order commensurate
structure is formed, (5 x 5) R arctan(3/4). All the ordered phases obtained by
adsorption at low temperature are metastable.
| 1992-09-14
| 2007-05-23
|
[
"cond-mat"
] |
Wei Li and Gianfranco Vidali
|
cond-mat/9209013
|
Quantum Lattice Fluctuations and Luminescence in C_60
|
We consider luminescence in photo-excited neutral C_60 using the
Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the
luminescence we use a collective coordinate method where our collective
coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon
mode and extrapolates between the ground state "dimerisation" and the exciton
polaron. There is good agreement for the existing luminescence peak spacing and
fair agreement for the relative intensity. We predict the existence of further
peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn,
36.90+f
| 1992-09-13
| 2007-05-23
|
[
"cond-mat"
] |
Barry Friedman, (Department of Physics and Texas Center for
Superconductivity, University of Houston, Texas and Department of Physics,
Sam Houston State University, Huntsville, Texas), Kikuo Harigaya,
(Fundamental Physics Section, Physical Science Division, Electrotechnical
Laboratory, Japan)
|
cond-mat/9209012
|
Completeness of the SO(4) Extended Bethe Ansatz for the One-Dimensional
Hubbard Model
|
We show how to construct a complete set of eigenstates of the hamiltonian of
the one-dimensional Hubbard model on a lattice of even length $L$. This is done
by using the nested Bethe Ansatz {\it and} the $SO(4)$ symmetry of the model.
We discuss in detail how the counting of independent eigenstates is carried
out.
| 1992-09-12
| 2009-10-22
|
[
"cond-mat"
] |
Fabian H.L. Essler, Vladimir E. Korepin, Kareljan Schoutens
|
cond-mat/9209009
|
Spin liquid phase for the frustrated Quantum Heisenberg Antiferromagnet
on a square lattice
|
The existance of a spin disordered ground state for the frustrated Quantum
Heisenberg Antiferromagnet on a square lattice is reconsidered. It is argued
that there is a unique action which is continuous through the whole phase
diagram, except at the Lifshitz point, so that the Neel and helicoidal states
can not coexist and there has to be an intermediate spin liquid state. To show
it, a detailed study combining Spin-Wave theory, Schwinger Bosons Mean Field
Theory and a scaling analysis of the appropriate hydrodynamic action is
performed. When done carefully, all these theories agree and strongly support
the existance of the spin liquThe manuscript has eight figures, which are
available upon request to the author. e-mail address is
ferrer@physics.rutgers.edu
| 1992-09-11
| 2009-10-22
|
[
"cond-mat"
] |
Jaime Ferrer
|
cond-mat/9209010
|
Study of spiral pattern formation in Rayleigh-Benard convection
|
We present a numerical study of a generalized two-dimensional Swift-Hohenberg
model of spiral pattern formation in Rayleigh-B\'enard convection in a
non-Boussinesq fluid. We demonstrate for the first time that a model for
convective motion is able to predict in considerable dynamical detail the
spontaneous formation of a rotating spiral state from an ordered hexagon state.
Our results are in good agreement with recent experimental studies of $CO_{2}$
gas. The mean flow and non-Boussinesq effects are shown to be crucial in
forming rotating spirals.
| 1992-09-11
| 2008-12-24
|
[
"cond-mat"
] |
Hao-wen Xi, J.D. Gunton, Jorge Vinals
|
cond-mat/9209011
|
Anisotropic Pairing on a Three-Band Fermi Surface for $A_3{\rm C}_{60}$
|
We study a model for anisotropic singlet pairing in $A_3{\rm C}_{60}$, using
a realistic model for the Fermi surface in a hypothesized
orientationally-ordered doped crystal. Anisotropic solutions are studied by
combining numerical solutions to the gap equation in the low-temperature phase
with a Landau expansion near the mean field critical temperature. We focus on a
class of three-dimensional nodeless $d$-wave solutions to the model, which
exhibit a fully developed gap everywhere on the Fermi surface, but non-BCS
temperature dependence of the order parameter in the condensed state, a
relatively large value of the low-temperature gap, $2\Delta/kT_{\rm c}$ , and
non-BCS structure in the quasiparticle spectrum near the gap.
| 1992-09-11
| 2009-10-22
|
[
"cond-mat"
] |
E. J. Mele and S. C. Erwin
|
cond-mat/9209008
|
A Simple Model for Coupled Magnetic and Quadrupolar Instabilities in
Uranium Heavy-Fermion Materials
|
We present a mean-field calculation of the phase diagram of a simple model of
localized moments, in the hexagonal uranium heavy-fermion compounds. The model
considers a non-Kramers quadrupolar doublet ground state magnetically coupled
with a singlet excited-state, favoring in-plane van-Vleck magnetism, as has
been conjectured for UPt$_3$. The Hamiltonian which defines the model is
Heisenberg like in both, magnetic and quadrupolar moments. Among our main
results are: (i) for zero intersite quadrupolar coupling, the magnetic order is
achieved by a first order transition above a critical intersite magnetic
coupling value which becomes second order at higher coupling strengths. (ii)
for finite intersite quadrupolar coupling, at temperatures below a second order
quadrupolar ordering transition, the minimal magnetic coupling value is
increased but (a) the magnetic ordering temperature is enhanced above this
value, and (b) the ordering of first and second order transitions in the phase
diagram is reversed.
| 1992-09-08
| 2009-10-22
|
[
"cond-mat"
] |
V. L. Libero and D. L. Cox
|
cond-mat/9209007
|
Spin texture in weakly doped $Cu0_2$ planes explaining magnetic
correlation length and Raman scattering experiments
|
A model of $CuO_2$ planes weakly doped with partially delocalised holes is
considered. The effect of such a hole on the background AFM spin texture can be
represented by a purely magnetic Hamiltonian $H = - \sum_{(ijk)} (\vec S_i
\cdot \vec S_j \times \vec S_k)^2$, where the summation is over the four
triangles of a single plaquette. We show that this model of randomly
distributed chiral spin defects leads to an in--plane spin correlation length
approximately described by $\xi^{-1} (x,T) = \xi^{-1} (0,T) + \xi^{-1} (x,0)$,
consistent with neutron scattering experiments on $La_{2-x}Sr_xCuO_4$. Further,
this model leads to favourable comparisons with $B_{1g}$ Raman scattering
results for the same cuprate system.
| 1992-09-08
| 2007-05-23
|
[
"cond-mat"
] |
R.J. Gooding, and A. Mailhot
|
cond-mat/9209005
|
Aspects of Spin Dynamics in the Cuprate Superconductors
|
One of the interesting aspects of the CuO superconductors is that
superconductivity is happening so close to the antiferromagnetic state. The
nuclear magnetic resonance and the recent neutron scattering experiments
clearly indicate that magnetic correlations persist in to the heavily doped
regime. In this paper we will discuss some of the details of the coupling of
the nuclear magnetic spin to the conduction electron spins. Furthermore we will
show that a simple band structure can explain the recent neutron scattering
data in the \LaSrCuO material for the optimal concentration of $x\approx 0.15$
if the lifetime effects are included.
| 1992-09-05
| 2007-05-23
|
[
"cond-mat"
] |
H. Monien (Institute for Theoretical Physics, Universty of California,
Santa Barbara, CA 93106)
|
cond-mat/9209006
|
Spin Gaps and Spin Dynamics in La_{2-x}Sr_xCuO_4 and YBa_2Cu_3O7_\delta
|
A magnetic susceptibility which decreases with decreasing temperature is
observed in all $CuO_2$ based superconductors with less than optimal doping. We
propose that in $La_{2-x} Sr_x CuO_4$ this is due to antiferromagnetic ordering
which is prevented by the low spatial dimensionality while in $YBa_2 Cu_3
O_{6.6}$ it is due to the interplay between antiferromagnetic fluctuations
within a plane and singlet pairing of electrons between nearest neighbor
planes.
| 1992-09-05
| 2009-01-23
|
[
"cond-mat"
] |
A. J. Millis (AT&T Bell Laboratories, Murray Hill, NJ) and H. Monien
(Institute for Theoretical Physics, UCSB, Santa Barbara, CA)
|
cond-mat/9209003
|
Interface roughening with a time-varying external driving force
|
We present a theoretical and numerical investigation of the effect of a
time-varying external driving force on interface growth. First, we derive a
relation between the roughening exponents which comes from a generalized
Galilean invariance, showing how the critical dimension of the model is tunable
with the external field. We further conjecture results for the exponents in two
dimensions, and find consistency with data obtained through simulations of two
models we expect to be in the same universality class. Finally, we discuss how
our results can be investigated experimentally.
| 1992-09-04
| 2010-12-17
|
[
"cond-mat"
] |
E. Hernandez-Garcia, T. Ala-Nissila, and Martin Grant
|
cond-mat/9209004
|
Combination Rules, Charge Symmetry, and Hall Effect in Cuprates
|
The rule relating the observed Hall coefficient to the spin and charge
responses of the uniform doped Mott insulator is derived. It is essential to
include the contribution of holon and spinon three-current correlations to the
effective action of the gauge field. In the vicinity of the Mott insulating
point the Hall coefficient is holon dominated and weakly temperature dependent.
In the vicinity of a point of charge conjugation symmetry the holon
contribution to the observed Hall coefficient is small: the Hall coefficient
follows the temperature dependence of the diamagnetic susceptibility with a
sign determined by the Fermi surface shape. NOTE: document prepared using
REVTEX. (3 Figs, not included, available on request from: ajs16@phx.cam.ac.uk)
| 1992-09-04
| 2009-10-22
|
[
"cond-mat"
] |
A.J. Schofield and J.M. Wheatley
|
cond-mat/9209002
|
New Exactly Solvable Model of Strongly Correlated Electrons Motivated by
High T_c Superconductivity
|
We present a new model describing strongly correlated electrons on a general
$d$-dimensional lattice. It differs from the Hubbard model by interactions of
nearest neighbours, and it contains the $t$-$J$ model as a special case. The
model naturally describes local electron pairs, which can move coherently at
arbitrary momentum. By using an $\eta$-pairing mechanism we can construct
eigenstates of the hamiltonian with off-diagonal-long-range-order (ODLRO).
These might help to relate the model to high-$T_c$ superconductivity. On a
one-dimensional lattice, the model is exactly solvable by Bethe Ansatz.
| 1992-09-03
| 2008-11-26
|
[
"cond-mat"
] |
Fabian H.L. Essler, Vladimir E. Korepin, Kareljan Schoutens
|
cond-mat/9208026
|
Electromagnetic response of a static vortex line in a type-II
superconductor : a microscopic study
|
The electromagnetic response of a pinned Abrikosov fluxoid is examined in the
framework of the Bogoliubov-de Gennes formalism. The matrix elements and the
selection rules for both the single photon (emission - absorption) and two
photon (Raman scattering) processes are obtained. The results reveal striking
asymmetries: light absorption by quasiparticle pair creation or single
quasiparticle scattering can occur only if the handedness of the incident
radiation is opposite to that of the vortex core states. We show how these
effects will lead to nonreciprocal circular birefringence, and also predict
structure in the frequency dependence of conductivity and in the differential
cross section of the Raman scattering.
| 1992-08-31
| 2009-10-22
|
[
"cond-mat"
] |
Boldizsar Janko and Joel D. Shore (Laboratory of Atomic and Solid
State Physics, Cornell University, Ithaca, New York)
|
cond-mat/9208025
|
Interfacial adsorption phenomena of the three-dimensional three-state
Potts model
|
We study the interfacial adsorption phenomena of the three-state
ferromagnetic Potts model on the simple cubic lattice by the Monte Carlo
method. Finite-size scaling analyses of the net-adsorption yield the evidence
of the phase transition being of first-order and $k_{\rm B} T_{\rm C} / J =
1.8166 (2)$.
| 1992-08-31
| 2009-10-22
|
[
"cond-mat"
] |
Atsushi Yamagata
|
cond-mat/9208027
|
Persistent spin and mass currents and Aharonov-Casher effect
|
Spin-orbit interaction produces persistent spin and mass currents in the ring
via the Aharonov-Casher effect. The experiment in $^3He-A_1$ phase, in which
this effect leads to the excitation of mass and spin supercurrent is proposed.
| 1992-08-31
| 2009-10-22
|
[
"cond-mat"
] |
A. V. Balatsky and B. L. Altshuler
|
cond-mat/9209001
|
The Constraint for the Lowest Landau Level and the Effective Field
Theory Approach for the Fractional Quantum Hall System
|
By applying the Dirac quantization method, we build the constraint that all
electrons are in the lowest Landau level into the Chern-Simons field theory
approach for the fractional quantum Hall system and show that the constraint
can be transmuted from hierarchy to hierarchy. For a finite system, we derive
that the action for each hierarchy can be split into two parts: a surface part
provides the action for the edge excitations while the remaining part is
precisely the bulk action for the next hierarchy. And the action for the edge
could be decoupled from the bulk only at the hierarchy filling.
| 1992-08-31
| 2007-05-23
|
[
"cond-mat"
] |
Zhong-Shui Ma and Zhao-Bin Su
|
cond-mat/9208024
|
Localized Electrons on a Lattice with Incommensurate Magnetic Flux
|
The magnetic field effects on lattice wavefunctions of Hofstadter electrons
strongly localized at boundaries are studied analytically and numerically. The
exponential decay of the wavefunction is modulated by a field dependent
amplitude J(t) which depends sensitively on the value of alpha (the magnetic
flux per plaquette in units of a flux quantum, t is the distance from the
boundary). While for rational values p/q, the envelope of J(t) increases as
2**t/q, the behavior for irrational alpha is erratic with an aperiodic
structure which changes drastically with alpha. For algebraic alpha it is found
that J(t) increases as a power law t**b(alpha) while it grows faster for
transcendental alpha. This is very different from the growth rate exp{sqrt(t)}
typical for random phases. The theoretical analysis is extended to lattices in
which the distances between adjacent layers increase as r**n with n>0.
Different behavior of J(t;n) is found in various regimes of n. It changes from
periodic for small n to random like for large n.
| 1992-08-29
| 2007-05-23
|
[
"cond-mat",
"hep-th"
] |
Shmuel Fishmen, Yonathan Shapir, and Xiang-Rong Wang
|
cond-mat/9208023
|
Self-Consistent Theory of Polymerized Membranes
|
We study $D$-dimensional polymerized membranes embedded in $d$ dimensions
using a self-consistent screening approximation. It is exact for large $d$ to
order $1/d$, for any $d$ to order $\epsilon=4-D$ and for $d=D$. For flat
physical membranes ($D=2,d=3$) it predicts a roughness exponent $\zeta=0.590$.
For phantom membranes at the crumpling transition the size exponent is
$\nu=0.732$. It yields identical lower critical dimension for the flat phase
and crumpling transition $D_{lc}(d)={2 d \over {d+1}}$ ($D_{lc}={\sqrt{2}}$ for
codimension 1). For physical membranes with ${\it random}$ quenched curvature
$\zeta=0.775$ in the new $T=0$ flat phase in good agreement with simulations.
| 1992-08-27
| 2009-01-23
|
[
"cond-mat"
] |
Pierre Le Doussal and Leo Radzihovsky
|
cond-mat/9208022
|
Electronic and structural properties of GaN by the full-potential LMTO
method : the role of the $d$ electrons
|
The structural and electronic properties of cubic GaN are studied within the
local density approximation by the full-potential linear muffin-tin orbitals
method. The Ga $3d$ electrons are treated as band states, and no shape
approximation is made to the potential and charge density. The influence of $d$
electrons on the band structure, charge density, and bonding properties is
analyzed. It is found that due to the energy resonance of the Ga 3$d$ states
with nitrogen 2$s$ states, the cation $d$ bands are not inert, and features
unusual for a III-V compound are found in the lower part of the valence band
and in the valence charge density and density of states. To clarify the
influence of the Ga $d$ states on the cohesive properties, additional full and
frozen--overlapped-core calculations were performed for GaN, cubic ZnS, GaAs,
and Si. The results show, in addition to the known importance of non-linear
core-valence exchange-correlation corrections, that an explicit description of
closed-shell repulsion effects is necessary to obtain accurate results for GaN
and similar systems. In summary, GaN appears to be somewhat exceptional among
the III-V compounds and reminiscent of II-VI materials, in that its band
structure and cohesive properties are sensitive to a proper treatment of the
cation $d$ bands, as a result of the presence of the latter in the valence band
range.
| 1992-08-27
| 2009-10-22
|
[
"cond-mat"
] |
Vincenzo Fiorentini, Michael Methfessel, and Matthias Scheffler
(Fritz-Haber-Institut der Max-Planck-Gesellschaft, BERLIN, Germany)
|
cond-mat/9208019
|
Dimerization and Energy-Level Structures in Fullerene Tubules
Investigated with an Electron-Phonon Model
|
Possible dimerization patterns and electronic structures in fullerene tubules
as the \pi-conjugated systems are studied with the extended Su-Schrieffer-
Heeger model. We assume various lattice geometries, including helical and
nonhelical tubules, and tubules with end caps. The model is solved for the
half-filling case of \pi-electrons. (1) When the undimerized systems do not
have a gap, the Kekul\'{e} structures tend to occur. These structures are
commensurate with the boundary condition in the direction perpendicular to the
tubular axis. The energy gap is of the order of the room temperatures at most.
Thus, the nearly metallic properties would be expected. (2) If the undimerized
systems have a large gap (\sim 1eV), the most stable structures are the
chain-like distortions where the direction of the arranged {\sl
trans}-polyacetylene chains is along almost the tubular axis. When we try to
obtain the Kekul\'{e} structures, the mismatch of the boundary condition occurs
and they are energetically unfavorable. The electronic structures are of
semiconductors due to the large gap.
| 1992-08-26
| 2007-05-23
|
[
"cond-mat"
] |
Kikuo Harigaya (Fundamental Physics Section, Electrotechnical
Laboratory, Japan), Mitsutaka Fujita (Institute of Materials Science,
University of Tsukuba, Japan)
|
cond-mat/9208017
|
Non-Gaussian distribution in Random advection dynamics
|
Simulations of vortex tube dynamics reveal that the non-Gaussian nature of
turbulent fluctuation originates in the effect of random advection. A similar
non-Gaussian distribution is found numerically in a simplified statistical
model of random advection. An analytical solution is obtained in the mean-field
case.
| 1992-08-26
| 2007-05-23
|
[
"cond-mat"
] |
Y-h. Taguchi and Hideki Takayasu
|
cond-mat/9208018
|
Homogeneous Isotropic Fluid Turbulence Simulated with the Lattice Vortex
Tube Model
|
Fully developed turbulence is analised with the lattice model employing
vortex tube representation which is introduced recently by the authors. Several
characteric features observed in experiments and direct numeric integrations
are reproduced. Not only Kolmogorov's inertial range is observed, but also
several local probability distribution functions are obtained as well. Those of
the local velocities are close to the Gaussian and exponential-like
distributions appear in local vorticity, relative velocities and local velocity
consisting of only higher wave number components. Coherent structure of vortex
tubes is seen, too. Moreover required cpu-time and memory-size are very little
comparing with the conventional pseudo-spectral method. keywords : fluid
turbulence, vortex tube, lattice model, numerical technic.
| 1992-08-26
| 2007-05-23
|
[
"cond-mat"
] |
Y-h. Taguchi and Hideki Takayasu
|
cond-mat/9208020
|
Frequency dependent conductivity of vortex cores in type II
superconductors
|
This paper is relevant to the recent optical transmission experiments of
Karrai et al. for vortices in high Tc superconductors. We begin with a
substantial review and introduction. The microscopic response of vortices is
calculated from the Bogoliubov-deGennes equation, including an equation of
motion and conductivity. We find that the expected resonant dipole transtition
is not present because of translation invariance. We consider the effect of
pinning and show that in the presence of pinning one recovers the dipole
resonance. Thus we conclude that pinning may play an important role in the
experiment.
| 1992-08-26
| 2009-10-22
|
[
"cond-mat"
] |
Ted Hsu
|
cond-mat/9208021
|
Mott Transition in the Hubbard model
|
In this article, I discuss W.Kohn's criterion for a metal insulator
transition, within the framework of a one band Hubbard model. This and related
ideas are applied to 1-dimensional Hubbard systems, and some intersting
miscellaneous results discussed. The Jordan Wigner transformation converting
the two species of fermions to two species of hardcore bosons is performed in
detail, and the ``extra phases'' arising from odd-even effects are explicitly
derived. Bosons are shown to prefer zero flux (i.e. diamagnetism), and the
corresponding ``happy fluxes'' for the fermions identified. A curious result
following from the interplay between orbital diamagnetism and spin polarization
is highlighted.
A ``spin-statistics'' like theorem, showing that the anticommutation
relations between fermions of opposite spin are crucial to obtain the SU(2)
invariance is pointed out.
| 1992-08-26
| 2015-06-25
|
[
"cond-mat"
] |
B.Sriram Shastry
|
cond-mat/9208016
|
Invariants of the Haldane-Shastry $SU(N)$ Chain
|
Using a formalism developed by Polychronakos, we explicitly construct a set
of invariants of the motion for the Haldane-Shastry $SU(N)$ chain.
| 1992-08-25
| 2009-10-22
|
[
"cond-mat",
"hep-th"
] |
Michael Fowler and Joseph A. Minahan
|
cond-mat/9208015
|
Number of solutions of the TAP equations for p--spin interaction spin
glasses
|
The number $\langle N_s\rangle$ of solutions of the equations of Thouless,
Anderson and Palmer for p--spin interaction spin glass models is calculated.
Below a critical temperature $T_c$ this number becomes exponentially large, as
it is in the SK--model ($p=2$). But in contrast to this, for any $p>2$ the
factor $\alpha(T)=N^{-1} \ln\langle N_s\rangle$ jumps discontinuously at
$T_c(p)$, which is consistent with the discontinuity occuring within the
mean--field theory for these models. For zero temperature the results obtained
by Gross and M\'ezard are reproduced, and for $p\rightarrow\infty$ one gets the
result for the random energy model.
| 1992-08-25
| 2009-10-22
|
[
"cond-mat"
] |
H. Rieger
|
cond-mat/9208014
|
Electron focusing, mode spectroscopy and mass enhancement in small
GaAs/AlGaAs rings
|
A new electron focusing effect has been discovered in small single and
coupled GaAs/AlGaAs rings. The focusing in the single ring is attributed solely
to internal orbits. The focusing effect allows the ring to be used as a small
mass spectrometer. The focusing causes peaks in the magnetoresistance at low
fields, and the peak positions were used to study the dispersion relation of
the one-dimensional magnetoelectric subbands. The electron effective mass
increases with the applied magnetic field by a factor of $50$, at a magnetic
field of $0.5T$. This is the first time this increase has been measured
directly. General agreement obtains between the experiment and the subband
calculations for straight channels.
| 1992-08-20
| 2009-10-22
|
[
"cond-mat"
] |
J Liu, K Ismail, KY Lee, JM Hong and S Washburn
|
cond-mat/9208013
|
Effect of Matrix Elements on the Pairing Kernel in Exchange Mediated
Superconductors
|
A method is derived for calculating the pairing kernel in exchange mediated
superconductors including matrix element effects. Various models for the
interaction vertex are considered, including spin exchange, orbital exchange,
and quadrupolar exchange. As an example, this formalism is applied to $UPt_3$
using relativistic wavefunctions from a local density band calculation.
| 1992-08-19
| 2009-10-22
|
[
"cond-mat"
] |
M. R. Norman
|
cond-mat/9208012
|
Suppression of tunneling by interference in half-integer--spin particles
|
Within a wide class of ferromagnetic and antiferromagnetic systems, quantum
tunneling of magnetization direction is spin-parity dependent: it vanishes for
magnetic particles with half-integer spin, but is allowed for integer spin. A
coherent-state path integral calculation shows that this topological effect
results from interference between tunneling paths.
| 1992-08-19
| 2009-01-23
|
[
"cond-mat"
] |
Daniel Loss, David P. DiVincenzo, and G. Grinstein (IBM)
|
cond-mat/9208011
|
Destructive quantum interference in spin tunneling problems
|
In some spin tunneling problems, there are several different but
symmetry-related tunneling paths that connect the same initial and final
configurations. The topological phase factors of the corresponding tunneling
amplitudes can lead to destructive interference between the different paths, so
that the total tunneling amplitude is zero. In the study of tunneling between
different ground state configurations of the Kagom\'{e}-lattice quantum
Heisenberg antiferromagnet, this occurs when the spin $s$ is half-odd-integer.
| 1992-08-15
| 2009-10-22
|
[
"cond-mat"
] |
Jan von Delft and Christopher L. Henley (Laboratory of Atomic and
Solid State Physics, Cornell University, Ithaca, NY)
|
cond-mat/9208010
|
Dynamic Scaling of Coupled Nonequilibrium Interfaces
|
We propose a simple discrete model to study the nonequilibrium fluctuations
of two locally coupled 1+1 dimensional systems (interfaces). Measuring
numerically the tilt-dependent velocity we construct a set of stochastic
continuum equations describing the fluctuations in the model
The scaling predicted by the equations are studied analytically using dynamic
renormalization group and compared with simulation results. When the coupling
is symmetric, the well known KPZ exponents are recovered. If one of the systems
is fluctuating independently, an increase in the roughness exponent is observed
for the other one.
| 1992-08-15
| 2009-10-22
|
[
"cond-mat"
] |
Albert-L\'aszl\'o Barab\'asi
|
cond-mat/9208009
|
Band Structure of the Fractional Quantum Hall Effect
|
The eigenstates of interacting electrons in the fractional quantum Hall phase
typically form fairly well defined bands in the energy space. We show that the
composite fermion theory gives insight into the origin of these bands and
provides an accurate and complete microscopic description of the strongly
correlated many-body states in the low-energy bands. Thus, somewhat like in
Landau's fermi liquid theory, there is a one-to-one correspondence between the
low energy Hilbert space of strongly interacting electrons in the fractinal
quantum Hall regime and that of weakly interacting electrons in the integer
quantum Hall regime.
| 1992-08-13
| 2009-10-22
|
[
"cond-mat"
] |
G. Dev and J.K. Jain
|
cond-mat/9208008
|
Multiple jumps and vacancy diffusion in a face-centered cubic metal
|
The diffusion of monovacancies in gold has been studied by computer
simulation. Multiple jumps have been found to play a central role in the atomic
dynamics at high temperature, and have been shown to be responsible for an
upward curvature in the Arrhenius plot of the diffusion coefficient.
Appropriate saddle points on the potential energy surface have been found,
supporting the interpretation of vacancy multiple jumps as distinct migration
mechanisms.
| 1992-08-12
| 2010-12-17
|
[
"cond-mat"
] |
G. De Lorenzi and F. Ercolessi
|
cond-mat/9208007
|
Selection Rules for Two Channel Kondo Models of U and Ce ions in Metals
|
Symmetry based selection rules are developed providing minimal criteria for
the existence of two-channel Kondo interactions between conduction electrons
and the low energy degrees of freedom on U$^{4+}$ and Ce$^{3+}$ in a metal
host, assuming that the underlying microscopics are regulated by the Anderson
Hamiltonian. An additional dynamic selection rule is imposed on Ce$^{3+}$ ions.
The selection rules restrict the two-channel quadrupolar Kondo effect to
U$^{4+}$ ions in cubic, tetragonal, and hexagonal symmetry. For hexagonal and
tetragonal symmetry, the Kondo effect for a U$^{4+}$ ion will always be
quadrupolar. The selection rules for Ce$^{3+}$ ions restrict the two-channel
magnetic Kondo effect to one of three possible doublet ionic ground states in
hexagonal symmetry and the lone doublet ionic ground state in cubic symmetry.
The dynamical selection rule apparently excludes two-channel Kondo behavior for
Yb$^{3+}$ ions.
| 1992-08-12
| 2009-10-22
|
[
"cond-mat"
] |
D.L. Cox (Department of Physics, The Ohio State University, Columbus,
Ohio, USA)
|
cond-mat/9208006
|
The Hubbard Model at Infinite Dimensions: Thermodynamic and Transport
Properties
|
We present results on thermodynamic quantities, resistivity and optical
conductivity for the Hubbard model on a simple hypercubic lattice in infinite
dimensions. Our results for the paramagnetic phase display the features
expected from an intuitive analysis of the one-particle spectra and
substantiate the similarity of the physics of the Hubbard model to those of
heavy fermion systems. The calculations were performed using an approximate
solution to the single-impurity Anderson model, which is the key quantity
entering the solution of the Hubbard model in this limit. To establish the
quality of this approximation we compare its results, together with those
obtained from two other widely used methods, to essentially exact quantum Monte
Carlo results.
| 1992-08-11
| 2009-10-22
|
[
"cond-mat"
] |
Th. Pruschke, D.L. Cox and M. Jarrell
|
cond-mat/9208004
|
The Electronic Spectrum of Fullerenes from the Dirac Equation
|
The electronic spectrum of sheets of graphite (plane honeycomb lattice)
folded into regular polihedra is studied. A continuum limit valid for
sufficiently large molecules and based on a tight binding approximation is
derived. It is found that a Dirac equation describes the flat graphite lattice.
Curving the lattice by insertion of odd numbered rings can be mimicked by
coupling effective gauge fields. In particular the $C_{60}$ and related
molecules are well described by the Dirac equation on the surface of a sphere
coupled to a color monopole sitting at its center.
| 1992-08-07
| 2009-10-22
|
[
"cond-mat",
"hep-th"
] |
J. Gonz\'alez, F. Guinea and M.A.H. Vozmediano
|
cond-mat/9208005
|
Topological Aspects of Spin and Statistics in Nonlinear Sigma Models
|
We study the purely topological restrictions on allowed spin and statistics
of topological solitons in nonlinear sigma models. Taking as space the
connected $d$-manifold $X$, and considering nonlinear sigma models with the
connected manifold $M$ as target space, topological solitons are given by
elements of $pi_d(M)$. Any topological soliton $\alpha \in \pi_d(M)$ determines
a quotient $\Stat_n(X,\alpha)$ of the group of framed braids on $X$, such that
choices of allowed statistics for solitons of type $\alpha$ are given by
unitary representations of $\Stat_n(X,\alpha)$ when $n$ solitons are present.
In particular, when $M = S^2$, as in the $O(3)$ nonlinear sigma model with Hopf
term, and $\alpha \in \pi_2(S^2)$ is a generator, we compute that
$\Stat_n(\R^2,\alpha) = \Z$, while $\Stat_n(S^2,\alpha) = \Z_{2n}$. It follows
that phase $\exp(i\theta)$ for interchanging two solitons of type $\alpha$ on
$S^2$ must satisfy the constraint $\theta = k\pi/n$, $k \in \Z$, when $n$ such
solitons are present.
| 1992-08-07
| 2008-11-26
|
[
"cond-mat"
] |
John Baez, Micheal Ody and William Richter
|
cond-mat/9208003
|
Complexity and criticality in Laplacian growth models
|
We analyze the dynamical evolution of systems which obey simple growth laws,
like diffusion limited aggregation or dielectric breakdown. We show that, if
the developing patterns is sufficiently complex, a scale invariant noise
spectrum is generated, in agreement with the hypothesis that the system is in a
self organized critical state. The intrinsic noise generated in the evolution
is shown to be independent of the (extrinsic) stochastic aspects of the growth.
Instead, it is related to the complexity of the generated pattern.
| 1992-08-07
| 2009-10-22
|
[
"cond-mat"
] |
F. Guinea, O. Pla and E. Louis
|
cond-mat/9208002
|
Transport Properties of the Infinite Dimensional Hubbard Model
|
Results for the optical conductivity and resistivity of the Hubbard model in
infinite spatial dimensions are presented. At half filling we observe a gradual
crossover from a normal Fermi-liquid with a Drude peak at $\omega=0$ in the
optical conductivity to an insulator as a function of $U$ for temperatures
above the antiferromagnetic phase transition. When doped, the ``insulator''
becomes a Fermi-liquid with a corresponding temperature dependence of the
optical conductivity and resistivity. We find a $T^2$-coefficient in the low
temperature resistivity which suggests that the carriers in the system acquire
a considerable mass-enhancement due to the strong local correlations. At high
temperatures, a crossover into a semi-metallic regime takes place.
| 1992-08-05
| 2009-10-22
|
[
"cond-mat"
] |
Th. Pruschke, D.L. Cox and M. Jarrell
|
cond-mat/9208001
|
Pressure Dependence of the Elastic Moduli in Aluminum Rich Al-Li
Compounds
|
I have carried out numerical first principles calculations of the pressure
dependence of the elastic moduli for several ordered structures in the
Aluminum-Lithium system, specifically FCC Al, FCC and BCC Li, L1_2 Al_3Li, and
an ordered FCC Al_7Li supercell. The calculations were performed using the full
potential linear augmented plane wave method (LAPW) to calculate the total
energy as a function of strain, after which the data was fit to a polynomial
function of the strain to determine the modulus. A procedure for estimating the
errors in this process is also given. The predicted equilibrium lattice
parameters are slightly smaller than found experimentally, consistent with
other LDA calculations. The computed elastic moduli are within approximately
10% of the experimentally measured moduli, provided the calculations are
carried out at the experimental lattice constant. The LDA equilibrium shear
modulus C11-C12 increases from 59.3 GPa in Al, to 76.0 GPa in Al_7Li, to 106.2
GPa in Al_3Li. The modulus C_44 increases from 38.4 GPa in Al to 46.1 GPa in
Al_7Li, then falls to 40.7 GPa in Al_3Li. All of the calculated elastic moduli
increase with pressure with the exception of BCC Li, which becomes elastically
unstable at about 2 GPa, where C_11-C_12 vanishes.
| 1992-08-03
| 2009-10-22
|
[
"cond-mat",
"hep-lat"
] |
Michael J. Mehl
|
cond-mat/9207028
|
Crystallography Without Periodicity
|
Text of a talk given at the International Colloquium on Group Theoretic
Methods in Physics, Salamanca, July, 1992. Another futile attempt to persuade
the world that space groups can be fun.
| 1992-07-31
| 2007-05-23
|
[
"cond-mat",
"hep-th"
] |
N. David Mermin
|
cond-mat/9207027
|
Critical Behavior of Charge Density Waves Below Threshold: Numerical and
Scaling Analysis
|
The critical behavior of pinned charge density waves (CDW's) is studied as
the threshold for sliding is approached. Using the Fukuyama-Lee-Rice
Hamiltonian with relaxational dynamics, the polarization and linear response
are calculated numerically. ... On the irreversible approach to threshold, the
response due to avalanches triggered by local instabilities dominates the
polarizability, which diverges in one and two dimensions. Characteristic
diverging length scales are studied using finite-size scaling of the
sample-to-sample variations of the threshold field in finite systems and
finite-size effects in the linear polarizability and the irreversible
polarization. A dominant diverging correlation length is found which controls
the threshold field distribution, finite-size effects in the irreversible
polarization, and a cutoff size for the avalanche size distribution. Our
results are compared with those for related models and questions are raised
concerning the relationship of the static critical behavior below threshold to
the dynamic critical behavior in the sliding state above threshold.
| 1992-07-27
| 2009-09-25
|
[
"cond-mat"
] |
Daniel S. Fisher and A. Alan Middleton
|
cond-mat/9207026
|
Critical exponents of the degenerate Hubbard model
|
We study the critical behaviour of the \SUN{} generalization of the
one-dimensional Hubbard model with arbitrary degeneracy $N$. Using the
integrability of this model by Bethe Ansatz we are able to compute the spectrum
of the low-lying excitations in a large but finite box for arbitrary values of
the electron density and of the Coulomb interaction. This information is used
to determine the asymptotic behaviour of correlation functions at zero
temperature in the presence of external fields lifting the degeneracy. The
critical exponents depend on the system parameters through a $N\times N$
dressed charge matrix implying the relevance of the interaction of charge- and
spin-density waves.
| 1992-07-24
| 2009-10-22
|
[
"cond-mat"
] |
Holger Frahm and Andreas Schadschneider
|
cond-mat/9207025
|
Chern-Simons superconductivity
|
We argue that a simple Yukawa coupling between the $O(3)$ nonlinear
$\s$-model and charged Dirac fermions leads, after one-loop quantum
corrections, to a Meissner effect, in the disordered phase of the nonlinear
$\s$-model.
| 1992-07-23
| 2011-04-20
|
[
"cond-mat",
"hep-th"
] |
D. Senechal
|
cond-mat/9207023
|
Melting a copper cluster: Critical droplet theory
|
We simulate the melting of a 71 A diameter cluster of Cu. At low temperatures
the crystal exhibits facets. With increasing temperatures the open facets
pre-melt, the melted regions coalesce into a liquid envelope containing a
crystalline nucleus, and the nucleus finally goes unstable to the supercooled
liquid. Using critical droplet theory and experimental data for Cu, we explain
the thermodynamics of the coexistence region. The width of the transition
scales as (Number of particles) to the power (-1/4).
| 1992-07-20
| 2015-06-25
|
[
"cond-mat"
] |
Ole H. Nielsen, James P. Sethna, Per Stoltze, Karsten W. Jacobsen and
Jens K. Norskov (Technical University of Denmark, Lyngby, Denmark)
|
cond-mat/9207024
|
Zero Frequency Current Noise for the Double Tunnel Junction Coulomb
Blockade
|
We compute the zero frequency current noise numerically and in several limits
analytically for the coulomb blockade problem consisting of two tunnel
junctions connected in series. At low temperatures over a wide range of
voltages, capacitances, and resistances it is shown that the noise measures the
variance in the number of electrons in the region between the two tunnel
junctions. The average current, on the other hand, only measures the mean
number of electrons. Thus, the noise provides additional information about
transport in these devices which is not available from measuring the current
alone.
| 1992-07-20
| 2009-10-22
|
[
"cond-mat"
] |
Selman Hershfield, John H. Davies, Per Hyldgaard, Christopher J.
Stanton, and John W. Wilkins
|
cond-mat/9207022
|
Cluster Algorithm for a Solid-On-Solid Model with Constraints
|
We adapt the VMR (valleys-to-mountains reflections) algorithm, originally
devised by us for simulations of SOS models, to the BCSOS model. It is the
first time that a cluster algorithm is used for a model with constraints. The
performance of this new algorithm is studied in detail in both phases of the
model, including a finite size scaling analysis of the autocorrelations.
| 1992-07-19
| 2009-10-22
|
[
"cond-mat",
"hep-lat"
] |
M. Hasenbusch, G. Lana, M. Marcu and K. Pinn
|
cond-mat/9207019
|
Duality in Multi-layered Quantum Hall Systems
|
The braid group dynamics captures the fractional quantum Hall effect (FQHE)
as a manifestation of puncture phase. When the dynamics is generalized for
particles on a multi-sheeted surface, we obtain new tools which determine the
fractional charges, the quantum statistics, and the filling factors of the
multi-layered FQHE. A many-quasi-hole wavefunction is proposed for the
bilayered samples. We also predict a $\nu = 5/7$ FQHE for triple-layered
samples. The viability of {\em 3-dimensional} FQHE and the application of the
concept of generalized duality to anyonic superconductivity are discussed.
| 1992-07-17
| 2007-05-23
|
[
"cond-mat"
] |
C. Ting
|
cond-mat/9207021
|
Nonlinear Meissner Effect in CuO Superconductors
|
Recent theories of the NMR in the CuO superconductors are based on a
spin-singlet $d_{x^2-y^2}$ order parameter. Since this state has nodal lines on
the Fermi surface, nonlinear effects associated with low-energy quasiparticles
become important, particularly at low temperatures. We show that the
field-dependence of the supercurrent, below the nucleation field for vortices,
can be used to locate the positions of the nodal lines of an unconventional gap
in momentum space, and hence test the proposed $d_{x^2-y^2}$ state.
| 1992-07-17
| 2009-01-23
|
[
"cond-mat"
] |
S.K. Yip and J.A. Sauls
|
cond-mat/9207020
|
Mutual statistics, braid group, and the fractional quantum Hall effect
|
We show that the notion of mutual statistics arises naturally from the
representation theory of the braid group over the multi-sheeted surface. A
Hamiltonian which describes particles moving on the double-sheeted surface is
proposed as a model for the bilayered fractional quantum Hall effect (FQHE)
discovered recently. We explicitly show that the quasi-holes of the bilayered
Hall fluid display fractional mutual statistics. A model for 3-dimensional FQHE
using the multi-layered sample is suggested.
| 1992-07-17
| 2015-06-25
|
[
"cond-mat"
] |
C. Ting
|
cond-mat/9207015
|
Fast-diffusion mean-field theory for k-body reactions in one dimension
|
We derive an improved mean-field approximation for k-body annihilation
reactions kA --> inert, for hard-core diffusing particles on a line,
annihilating in groups of k neighbors with probability 0 < q <= 1. The hopping
and annihilation processes are correlated to mimic chemical reactions. Our new
mean-field theory accounts for hard-core particle properties and has a larger
region of applicability than the standard chemical rate equation especially for
large k values. Criteria for validity of the mean-field theory and its use in
phenomenological data fits are derived. Numerical tests are reported for
k=3,4,5,6.
| 1992-07-15
| 2014-10-13
|
[
"cond-mat"
] |
V. Privman, M. D. Grynberg
|
cond-mat/9207014
|
Morphology of Amorphous Layers Ballistically Deposited on a Planar
Substrate
|
We report numerical simulation of the deposition of spherical particles on a
planar surface, by ballistic, straight-line trajectory transport, and assuming
irreversible adhesion on contact with the surface or previously deposited
particles. Our data indicate that the deposit formed has a loosely layered
structure within few diameters from the surface. This structure can be
explained by a model of growth via chain formation. Away from the surface we
found evidence of a monotonic, power-law approach to the bulk density. Both
density and contact-statistics results suggest that the deposit formed is
sparse: the space-filling fraction is about 15%, and the average number of
contacts is 2. The morphology of the deposit both near the surface and in the
bulk seems to be a result of competition of screening and branching; nearly
half of all the spheres are either single-contact dangling ends, or branching
nodes with more than two contacts.
| 1992-07-15
| 2014-10-13
|
[
"cond-mat"
] |
B. D. Lubachevsky, V. Privman, S.C. Roy
|
cond-mat/9207018
|
Vortex motion and the Hall effect in type II superconductors: a time
dependent Ginzburg-Landau theory approach
|
Vortex motion in type II superconductors is studied starting from a variant
of the time dependent Ginzburg-Landau equations, in which the order parameter
relaxation time is taken to be complex. Using a method due to Gor'kov and
Kopnin, we derive an equation of motion for a single vortex ($B\ll H_{c2}$) in
the presence of an applied transport current. The imaginary part of the
relaxation time and the normal state Hall effect both break ``particle-hole
symmetry,'' and produce a component of the vortex velocity parallel to the
transport current, and consequently a Hall field due to the vortex motion.
Various models for the relaxation time are considered, allowing for a
comparison to some phenomenological models of vortex motion in superconductors,
such as the Bardeen-Stephen and Nozi\`eres-Vinen models, as well as to models
of vortex motion in neutral superfluids. In addition, the transport energy,
Nernst effect, and thermopower are calculated for a single vortex. Vortex
bending and fluctuations can also be included within this description,
resulting in a Langevin equation description of the vortex motion. The Langevin
equation is used to discuss the propagation of helicon waves and the
diffusional motion of a vortex line. The results are discussed in light of the
rather puzzling sign change of the Hall effect which has been observed in the
mixed state of the high temperature superconductors.
| 1992-07-15
| 2008-11-26
|
[
"cond-mat"
] |
Alan T. Dorsey
|
cond-mat/9207016
|
Ferromagnetism of the 1-D Kondo Lattice Model: A Quantum Monte Carlo
Study
|
The one dimensional Kondo lattice model is investigated using Quantum Monte
Carlo and transfer matrix techniques. In the strong coupling region
ferromagnetic ordering is found even at large band fillings. In the weak
coupling region the system shows an RKKY like behavior.
| 1992-07-15
| 2007-05-23
|
[
"cond-mat"
] |
Matthias Troyer and Diethelm W\"urtz
|
cond-mat/9207017
|
Transport Properties and Fluctuations in Type II Superconductors Near
$H_{c2}$
|
We study the flux-flow Hall effect and thermomagnetic transport near the
upper critical field \hctwo\ in extreme type-II superconductors starting from a
suitable generalization of the time dependent Ginzburg-Landau equations. We
explicitly incorporate the effects of backflow into the calculations of the
local electric field and current, leading to a current which is properly
divergenceless. The Hall conductivity calculated from this current agrees with
other mean-field calculations which assume a uniform applied electric field
(the Schmid-Caroli-Maki solution), thereby vindicating these simplified
treatments. We then use these results to calculate the transverse
thermomagnetic effects (the Ettingshausen and Nernst effects). The effects of
thermal fluctuations and nonlocal elasticity of the flux lattice are
incorporated using a method recently developed by Vecris and Pelcovits [G.
Vecris and R. A. Pelcovits, Phys. Rev. B {\bf 44}, 2767 (1991)]. Our results,
taken together with those of Vecris and Pelcovits, provide a rather complete
description of the transport properties of the flux lattice state near \hctwo,
at least within the framework of time dependent Ginzburg-Landau theory.
| 1992-07-15
| 2009-10-22
|
[
"cond-mat"
] |
Robert J. Troy and Alan T. Dorsey
|
cond-mat/9207013
|
The Majorana Fermions for Quantum S=1/2 Antiferromagnet?
|
Recently it has been suggested by A. M. Tsvelik that quantum S=1/2
antiferromagnet can be described by the Majorana fermions in an irreducible way
and without any constraint. In contrast to this claim we shall show that this
representation is highly reducible. It is a direct sum of four irreducible
fundamental representations of $su(2)$ algebra.
| 1992-07-14
| 2007-05-23
|
[
"cond-mat"
] |
Alexander Moroz
|
cond-mat/9207012
|
Magnetic and Dynamic Properties of the Hubbard Model in Infinite
Dimensions
|
An essentially exact solution of the infinite dimensional Hubbard model is
made possible by using a self-consistent mapping of the Hubbard model in this
limit to an effective single impurity Anderson model. Solving the latter with
quantum Monte Carlo procedures enables us to obtain exact results for the one
and two-particle properties of the infinite dimensional Hubbard model. In
particular we find antiferromagnetism and a pseudogap in the single-particle
density of states for sufficiently large values of the intrasite Coulomb
interaction at half filling. Both the antiferromagnetic phase and the
insulating phase above the N\'eel temperature are found to be quickly
suppressed on doping. The latter is replaced by a heavy electron metal with a
quasiparticle mass strongly dependent on doping as soon as $n<1$. At half
filling the antiferromagnetic phase boundary agrees surprisingly well in shape
and order of magnitude with results for the three dimensional Hubbard model.
| 1992-07-10
| 2009-10-22
|
[
"cond-mat"
] |
M. Jarrell and Thomas Pruschke
|
cond-mat/9207011
|
Numerical study of pattern formation following a convective instability
in non-Boussinesq fluids
|
We present a numerical study of a model of pattern formation following a
convective instability in a non-Boussinesq fluid. It is shown that many of the
features observed in convection experiments conducted on $CO_{2}$ gas can be
reproduced by using a generalized two-dimensional Swift-Hohenberg equation. The
formation of hexagonal patterns, rolls and spirals is studied, as well as the
transitions and competition among them. We also study nucleation and growth of
hexagonal patterns and find that the front velocity in this two dimensional
model is consistent with the prediction of marginal stability theory for one
dimensional fronts.
| 1992-07-10
| 2009-10-22
|
[
"cond-mat"
] |
Hao-wen Xi, Jorge Vinals and J.D. Gunton
|
cond-mat/9207010
|
Unstable Periodic Orbits in the Stadium Billiard
|
A systematic numerical technique for the calculation of unstable periodic
orbits in the stadium billiard is presented. All the periodic orbits up to
order $p=11$ are calculated and then used to calculate the average Lyapunov
exponent and the topological entropy. Applications to semiclassical
quantization and to experiments in mesoscopic systems and microwave cavities
are noted.
| 1992-07-09
| 2009-10-22
|
[
"cond-mat"
] |
Ofer Biham and Mark Kvale
|
cond-mat/9207009
|
Modification of the Magnetic Flux-Line Interaction at a Superconductor's
Surface
|
The pair interaction between magnetic flux lines in a semi-infinite slab of
an anisotropic type-II superconductor in an external field is derived in the
London limit. The case where the applied field is normal to the
superconductor/vacuum interface is considered. The presence of stray fields
near the surface leads to an additional contribution to the repulsive
interaction between flux lines that vanishes exponentially with the distance
from the interface. The pair interaction is used to obtain the continuum
elastic energy of a distorted semi-infinite flux-line array. The presence of
the superconductor/vacuum interface yields surface contributions to the
compressional and tilt elastic constants.
| 1992-07-08
| 2007-05-23
|
[
"cond-mat"
] |
M. Cristina Marchetti (Syracuse Univ.)
|
cond-mat/9207008
|
Vortex Line Fluctuations in Model High Temperature Superconductors
|
We carry out Monte Carlo simulations of the uniformly frustrated 3d XY model
as a model for vortex line fluctuations in a high Tc superconductor. A density
of vortex lines of f=1/25 is considered. We find two sharp phase transitions.
The low T phase is an ordered vortex line lattice. The high T normal phase is a
vortex line liquid with much entangling, cutting, and loop excitations. An
intermediate phase is found which is characterized as a vortex line liquid of
disentangled lines. In this phase, the system displays superconducting
properties in the direction parallel to the magnetic field, but normal behavior
in planes perpendicular to the magnetic field.
| 1992-07-07
| 2009-10-22
|
[
"cond-mat"
] |
Ying-Hong Li (ITP Utrecht) and S. Teitel (U of Rochester)
|
cond-mat/9207006
|
Phase Diagram of a Lattice Microemulsion Model in Two Dimensions
|
The phase diagram of a lattice microemulsion model proposed by Ciach, H{\o}ye
and Stell is studied using mean-field theory and Monte Carlo simulations.
Surfactant directional degrees of freedom are summed out exactly before
mean-field theory is applied, and the resulting phase diagrams are much
improved compared with previous mean-field results. The critical line and
tricritical point is located using Monte Carlo simulations and finite size
scaling.
| 1992-07-06
| 2009-10-22
|
[
"cond-mat"
] |
Per Arne Slotte
|
cond-mat/9207007
|
Low voltage conductance of small tunnel junctions
|
A discrete charge transfer in a small tunnel junction where Coulomb
interactions are important can excite electron-hole pairs near the Fermi level.
We use a simple model to study the associated nonequilibrium properties and
found two novel effects: (i) for junctions with electrodes of the same
electronic properties, a leakage current exists within the Coulomb gap even
when the environmental impedance is infinite; (ii) for junctions with
electrodes of different electronic properties, the differential conductance
diverges when a net interaction between conduction electrons is attractive, and
it is strongly suppressed for a net repulsive interaction.
| 1992-07-06
| 2007-05-23
|
[
"cond-mat"
] |
F. Guinea and M. Ueda
|
cond-mat/9207005
|
On the Harmonic Oscillator Regularization of Partition Functions
|
A convenient way to calculate $N$-particle quantum partition functions is by
confining the particles in a weak harmonic potential instead of using a finite
box or periodic boundary conditions. There is, however, a slightly different
connection between partition functions and thermodynamic quantities with such
volume regularization. This is made explicit, and its origin explained to be
due to the system having a space-varying density in an external potential.
Beyond perturbation theory there is a potential pitfall with the method, which
is pointed out.
| 1992-07-04
| 2007-05-23
|
[
"cond-mat"
] |
K{\aa}re Olaussen
|
cond-mat/9207004
|
Random Sequential Adsorption on a Line: Mean-Field Theory of Diffusional
Relaxation
|
We develop a new fast-diffusion approximation for the kinetics of deposition
of extended objects on a linear substrate, accompanied by diffusional
relaxation. This new approximation plays the role of the mean-field theory for
such processes and is valid over a significantly larger range than an earlier
variant, which was based on a mapping to chemical reactions. In particular,
continuum-limit off-lattice deposition is described naturally within our
approximation. The criteria for the applicability of the mean-field theory are
derived. While deposition of dimers, and marginally, trimers, is affected by
fluctuations, we find that the k-mer deposition kinetics is asymptotically
mean-field like for all k=4,5,..., where the limit k->infinity, when properly
defined, describes deposition-diffusion kinetics in the continuum.
| 1992-07-03
| 2010-10-12
|
[
"cond-mat"
] |
Vladimir Privman and Mustansir Barma
|
cond-mat/9207003
|
Fluctuating Interfaces, Surface Tension, and Capillary Waves: An
Introduction
|
We present an introduction to modern theories of interfacial fluctuations and
the associated interfacial parameters: surface tension and surface stiffness,
as well as their interpretation within the capillary wave model. Transfer
matrix spectrum properties due to fluctuation of an interface in a
long-cylinder geometry are reviewed. The roughening transition and properties
of rigid interfaces below the roughening temperature in 3d lattice models are
surveyed with emphasis on differences in fluctuations and transfer matrix
spectral properties of rigid vs. rough interfaces.
| 1992-07-02
| 2014-10-13
|
[
"cond-mat",
"astro-ph",
"hep-lat"
] |
Vladimir Privman
|
cond-mat/9207002
|
Model of Cluster Growth and Phase Separation: Exact Results in One
Dimension
|
We present exact results for a lattice model of cluster growth in 1D. The
growth mechanism involves interface hopping and pairwise annihilation
supplemented by spontaneous creation of the stable-phase, +1, regions by
overturning the unstable-phase, -1, spins with probability p. For cluster
coarsening at phase coexistence, p=0, the conventional structure-factor scaling
applies. In this limit our model falls in the class of diffusion-limited
reactions A+A->inert. The +1 cluster size grows diffusively, ~t**(1/2), and the
two-point correlation function obeys scaling. However, for p>0, i.e., for the
dynamics of formation of stable phase from unstable phase, we find that
structure-factor scaling breaks down; the length scale associated with the size
of the growing +1 clusters reflects only the short-distance properties of the
two-point correlations.
| 1992-07-02
| 2014-10-13
|
[
"cond-mat",
"hep-lat"
] |
Vladimir Privman
|
cond-mat/9207001
|
Exact Results for a Three-Body Reaction-Diffusion System
|
A system of particles hopping on a line, singly or as merged pairs, and
annihilating in groups of three on encounters, is solved exactly for certain
symmetrical initial conditions. The functional form of the density is nearly
identical to that found in two-body annihilation, and both systems show
non-mean-field, ~1/t**(1/2) instead of ~1/t, decrease of particle density for
large times.
| 1992-07-02
| 2010-10-12
|
[
"cond-mat",
"hep-lat"
] |
Vladimir Privman
|
cond-mat/9206011
|
Correlations for the S=1/2 Antiferromagnet on a Truncated Tetrahedron
|
The antiferromagnetic Heisenberg Hamiltonian is investigated on a truncated
tetrahedron, which is a closed 12 site system. We find that the ground state
has many similarities to that of $C_{60}$. We study 2- and 4-spin correlations
in the classical ground state of the truncated tetrahedron and calculate the
same correlations in the exact S=1/2 ground state. We find that the classical
correlations survive for a range of bond strengths in the Heisenberg
Hamiltonian and that one can construct a good trial wavefunction based on the
classical ground state. This suggests that the correlations present in the
classical ground state of $C_{60}$ also survive in the exact ground state of
that system, for a range of bond strengths about the physically relevant $J_2
\approx J_1$. We calculate the momentum-space correlation function $S ( q )$,
which is measurable by neutron scattering, for both $C_{12}$ and $C_{60}$. We
also calculate correlations at finite temperature.
| 1992-06-26
| 2009-10-22
|
[
"cond-mat"
] |
D. Coffey and S. A. Trugman
|
cond-mat/9206010
|
Magnetic Properties of Undoped $C_{60}$
|
The Heisenberg antiferromagnet, which arises from the large $U$ Hubbard
model, is investigated on the $C_{60}$ molecule and other fullerenes. The
connectivity of $C_{60}$ leads to an exotic classical ground state with
nontrivial topology. We argue that there is no phase transition in the Hubbard
model as a function of $U/t$, and thus the large $U$ solution is relevant for
the physical case of intermediate coupling. The system undergoes a first order
metamagnetic phase transition. We also consider the S=1/2 case using
perturbation theory. Experimental tests are suggested.
| 1992-06-26
| 2009-10-22
|
[
"cond-mat"
] |
D. Coffey and S. A. Trugman
|
cond-mat/9206009
|
Quantum Field Theories on Manifolds with Curved Boundaries: Scalar
Fields
|
A framework allowing for perturbative calculations to be carried out for
quantum field theories with arbitrary smoothly curved boundaries is described.
It is based on an expansion of the heat kernel derived earlier for arbitrary
mixed Dirichlet and Neumann boundary conditions.
The method is applied to a general renormalisable scalar field theory in four
dimensions using dimensional regularisation to two loops and expanding about
arbitrary background fields. Detailed results are also specialised to an $O(n)$
symmetric model with a single coupling constant. Extra boundary terms are
introduced into the action which give rise to either Dirichlet or generalised
Neumann boundary conditions for the quantum fields. For plane boundaries the
resulting renormalisation group functions are in accord with earlier results
but here the additional terms depending on the extrinsic curvature of the
boundary are found. Various consistency relations are also checked and the
implications of conformal invariance at the critical point where the $\beta$
function vanishes are also derived. The local Scr\"odinger equation for the
wave functional defined by the functional integral under deformations of the
boundary is also verified to two loops. Its consistency with the
renormalisation group to all orders in perturbation theory is discussed.
| 1992-06-26
| 2016-08-31
|
[
"cond-mat"
] |
D.M. McAvity and H. Osborn
|
cond-mat/9206008
|
The Nonequilibrium Dynamics of Driven Line Liquids
|
We study the nonequilibrium dynamics of line liquids as realized in the
nonlinear motion of flux lines of a superconductor driven by an applied
electric current. Our analysis suggests a transition in the dynamics of the
lines from a smooth, laminar phase at small driving forces, to a rough,
turbulent phase when the drive is increased. We explore the nature of these
phases and describe interesting analogies to driven diffusion and growing
interfaces.
| 1992-06-24
| 2009-10-22
|
[
"cond-mat"
] |
Terence Hwa
|
cond-mat/9206007
|
New Fermionic Description of Quantum S = 1/2 Antiferromargnet
|
A novel approach to S =1/2 antiferromagnets with strong fluctuations based on
the representation of spin-1/2 operators as bylinear forms of real (Majorana)
fermions is suggested. This representation has the advantage of being
irreducible without any constraints on the fermionic Hilbert space. This
property allows to derive an effective Hamiltonian for low-lying excitations in
the spin liquid state. It is proven that these excitations are S = 1 real
fermions.
| 1992-06-19
| 2009-10-22
|
[
"cond-mat"
] |
A. M. Tsvelik
|
cond-mat/9206006
|
Directed Polymer Blends and Quantum Critical Phenomena
|
The statistical mechanics of directed line-like objects, such as directed
polymers in an external field, strands of dipoles in both ferro- and
electrorheological fluids, and flux lines in high-$T_{\tiny C}$ superconductors
bears a close resemblance to the quantum mechanics of bosons in $2+1$
dimensions. We show that single component and binary mixture critical phenomena
in these systems are in the universality class of three dimensional uniaxial
dipolar ferromagnets and ferroelectrics. Our results also apply to films of two
superfluid species undergoing phase separation well below their
$\lambda$-points near $T=0$. In the case of directed polymers and
electrorheological fluids we analyze the effects of free ends occurring in the
sample as well as a novel directionally-dependent compressibility.
| 1992-06-18
| 2009-10-22
|
[
"cond-mat"
] |
Randall D. Kamien and David R. Nelson
|
cond-mat/9206005
|
Dimensional Reduction of a Generalized Flux Problem
|
A generalized flux problem with Abelian and non-Abelian fluxes is considered.
In the Abelian case we shall show that the generalized flux problem for
tight-binding models of noninteracting electrons on either $2n$ or $2n+1$
dimensional lattice can always be reduced to a $n$ dimensional hopping problem.
A residual freedom in this reduction enables to identify equivalence classes of
hopping Hamiltonians which have the same spectrum. In the non-Abelian case the
reduction is not possible in general unless the flux tensor factorizes into an
Abelian one times an element of the corresponding algebra.
| 1992-06-18
| 2009-10-22
|
[
"cond-mat",
"hep-lat",
"hep-th"
] |
Alexander Moroz
|
cond-mat/9206004
|
New Dynamic Monte Carlo Renormalization Group Method
|
The dynamical critical exponent of the two-dimensional spin-flip Ising model
is evaluated by a Monte Carlo renormalization group method involving a
transformation in time. The results agree very well with a finite-size scaling
analysis performed on the same data. The value of $z = 2.13 \pm 0.01$ is
obtained, which is consistent with most recent estimates.
| 1992-06-13
| 2009-10-22
|
[
"cond-mat"
] |
Martin-D. Lacasse (1), Jorge Vinals (2), Martin Grant(1) ((1) Centre
for the Physics of Materials and Department of Physics, McGill University,
Rutherford Building, Montr\'eal, Qu\'ebec, Canada (2) Supercomputer
Computations Research Institute, Florida State University, Tallahassee,
Florida)
|
cond-mat/9206003
|
Interactions for odd-omega gap singlet superconductors
|
A class of singlet superconductors with a gap function $\Delta({\bf k},
\omega_n)$ which is {\it odd} in both momentum and Matsubara frequency was
proposed recently \cite{ba}. To show an instability in the {\it odd} gap
channel, a model phonon propagator was used with the $p$-wave interaction
strength larger than the $s$-wave. We argue that the positive scattering matrix
element entering the Eliashberg equations leads to a constraint on the relative
strength of $p$- and $s$-wave interactions which inhibits odd pairing. However,
a general spin dependent electron-electron interaction can satisfy all
constraints and produce the odd singlet gap. A possibility which may lead to an
odd gap is a strongly antiferromagnetically correlated system, such as a
high-$T_c$ material.
| 1992-06-10
| 2009-10-22
|
[
"cond-mat"
] |
Elihu Abrahams(Rutgers), Alexander Balatsky(Los Alamos), J.R.
Schrieffer(NHMFL), Philip B. Allen(SUNY)
|
cond-mat/9206002
|
Twisted Boundary Conditions and the Adiabatic Ground State for the
Attractive XXZ Luttinger Liquid
|
The one-dimensional attractive lattice fermion gas equivalent to the
Heisenberg-Ising spin 1/2 chain is studied for a ring geometry threaded by
magnetic flux. We find that for charged fermions having interaction strength
$\Delta=\cos(\pi / p)$ with $p$ {\it noninteger}, the adiabatic ground state is
periodic in the magnetic flux threading the chain, with period 2 flux quanta,
as found by Shastry and Sutherland for the repulsive case. We find that, at
particular values of the threading field, a sequence of initially zero-energy
bound states form at the Fermi surface during the adiabatic process, the
largest containing $[p]$ (the integer part of $p$) fermions. This largest bound
state moves around to the other Fermi point and sequentially unbinds. We find
Berry's Phase for the whole process to be $[p] \pi$. For $p$ {\it integer}, as
$\Phi$ increases, eventually all the particles in the system go into bound
states of size $[p]$. The period in this case is of order the size of the
system.
| 1992-06-03
| 2009-10-22
|
[
"cond-mat"
] |
Naichang Yu and Michael Fowler
|
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