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6,900 | The Mott-Hubbard Transition on the D=infinity Bethe Lattice | cond-mat.str-el | In view of a recent controversy we investigated the Mott-Hubbard transition
in D=infinity with a novel cluster approach. i) We show that any truncated
Bethe lattice of order n can be mapped exactly to a finite Hubbard-like
cluster. ii) We evaluate the self-energy numerically for n=0,1,2 and compare
with a series of sel... | physics |
6,901 | Questions and Issues Arising at SCES '94 Theory | cond-mat.str-el | I summarize some of the key questions to have emerged during the 1994
conference on ``Strongly Correlated Electron Systems'', held in Amsterdam,
August 1994. Issues addressed include: Hunds rule interactions and how they
renormalize; the Luttinger sum rule and metamagnetism; heavy fermion
insulators, the nature of the ... | physics |
6,902 | The Hubbard Model: Introduction and Selected Rigorous Results | cond-mat.str-el | The Hubbard model is a "highly oversimplified model" for electrons in a solid
which interact with each other through extremely short ranged repulsive
(Coulomb) interaction. The Hamiltonian of the Hubbard model consists of two
pieces; H_hop which describes quantum mechanical hopping of electrons, and Hint
which describe... | physics |
6,903 | Spin-gap phase in nearly-half-filled one-dimensional conductors coupled with phonons | cond-mat.str-el | Asymptotic properties of nearly-half-filled one-dimensional conductors
coupled with phonons are studied through a renormalization group method. Due to
spin-charge coupling via electron-phonon interaction, the spin correlation
varies with filling as well as the charge correlation. Depending on the
relation between cut-o... | physics |
6,904 | Non Fermi-Liquid States and Pairing of a general Model of Copper-Oxide Metals | cond-mat.str-el | A model of copper-oxygen bonding and anti-bonding bands with the most general
two-body interactions allowable by symmetry is considered. The model has a
continuous transition as a function of hole-density x and temperature T to a
phase in which a current circulates in each unit cell. This phase preserves the
translatio... | physics |
6,905 | On two channel flavor anisotropic and one channel compactified Kondo models | cond-mat.str-el | We reinvestigate the two channel flavor anisotropic model (2CFAK) and one
channel compacitified Kondo model (1CCK). For these two models, all the
possible fixed points and their symmetries are identified; the finite size
spectra, the electron conductivity and pairing susceptibility are calculated.
It is shown that the ... | physics |
6,906 | Solution of two channel spin-flavor Kondo model | cond-mat.str-el | We investigate a model where an impurity couples to both the spin and the
flavor currents of the two channel conduction electrons. This model can be used
as a prototype model of a magnetic impurity tunneling between two sites in a
metal and of some heavy fermion systems where the ground state of the impurity
has a four... | physics |
6,907 | Solution of effective Hamiltonian of impurity hopping between two sites in a metal | cond-mat.str-el | We analyze in detail all the possible fixed points of the effective
Hamiltonian of a non-magnetic impurity hopping between two sites in a metal
obtained by Moustakas and Fisher(MF). We find a line of non-fermi liquid fixed
points which continuously interpolates between the 2-channel Kondo fixed
point(2CK) and the one c... | physics |
6,908 | Itinerant Antiferromagnetism in FeGe_2 | cond-mat.str-el | FeGe_2, and lightly doped compounds based on it, have a Fermi surface driven
instability which drive them into an incommensurate spin density wave state.
Studies of the temperature and magnetic field dependence of the resistivity
have been used to determine the magnetic phase diagram of the pure material
which displays... | physics |
6,909 | Zero-bias anomalies of point contact resistance due to adiabatic electron renormalization of dynamical defects | cond-mat.str-el | We study effect of the adiabatic electron renormalization on the parameters
of the dynamical defects in the ballistic metallic point contact. The upper
energy states of the ``dressed'' defect are shown to give a smaller
contribution to a resistance of the contact than the lower energy ones. This
holds both for the "cla... | physics |
6,910 | Low energy properties of M-state tunneling systems in metals: New candidates for non-Fermi-liquid systems | cond-mat.str-el | We construct a generalized multiplicative renormalization group
transformation to study the low energy dynamics of a heavy particle tunneling
among $M$ different positions and interacting with $N_f$ independent conduction
electron channels. Using a $1/N_f$-expansion we show that this M-level scales
towards a fixed poin... | physics |
6,911 | Mean field approach to antiferromagnetic domains in the doped Hubbard model | cond-mat.str-el | We present a restricted path integral approach to the 2D and 3D repulsive
Hubbard model. In this approach the partition function is approximated by
restricting the summation over all states to a (small) subclass which is chosen
such as to well represent the important states. This procedure generalizes mean
field theory... | physics |
6,912 | Transport and magnetic properties of La$_{1-x}$Ca$_x$VO$_3$ | cond-mat.str-el | We report the temperature dependence of transport and magnetic properties of
La$_{1-x}$Ca$_x$VO$_3$ for x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5. The system
exhibits an insulator-to-metal transition concomitant with an
antiferromagnetic-to-paramagnetic transition near x = 0.2 with increasing
substitution. Disorder effects a... | physics |
6,913 | Quantum Monte Carlo study of the pairing correlation in the Hubbard ladder | cond-mat.str-el | An extensive Quantum Monte Carlo calculation is performed for the two-leg
Hubbard ladder model to clarify whether the singlet pairing correlation decays
slowly, which is predicted from the weak-coupling theory but controversial from
numerical studies. Our result suggests that the discreteness of energy levels
in finite... | physics |
6,914 | Instabilities in Chains Coupled by Two-Body Interactions | cond-mat.str-el | We derive a general set of Poor Man's scaling equations and analyze the
stability of the Luttinger state in a system composed of a finite number N of
one dimensional spinless fermionic chains, coupled through a general two body
interaction. The effect of processes with momentum transfer parallel to the
Fermi surface in... | physics |
6,915 | Electronic Properties Of Buckminsterfullerenes: Degeneracies and Surprises | cond-mat.str-el | Buckminsterfullerene compounds exibit remarkable physics at low temperatures,
e.g. high temperature superconductivity in alkali-fullerenes, and
ferromagnetism in TDAE -C60. Here we review recent theoretical studies of
electron correlations in these compounds. In particular, we discuss models of
electron-vibron interact... | physics |
6,916 | Transport phenomenology for a holon-spinon fluid | cond-mat.str-el | We propose that the normal-state transport in the cuprate superconductors can
be understood in terms of a two-fluid model of spinons and holons. In our
scenario, the resistivity is determined by the properties of the holons while
magnetotransport involves the recombination of holons and spinons to form
physical electro... | physics |
6,917 | Normal Helium 3: a Mott-Stoner liquid | cond-mat.str-el | A physical picture of normal liquid $^3$He, which accounts for both ``almost
localized'' and ``almost ferromagnetic'' aspects, is proposed and confronted to
experiments. | physics |
6,918 | Ground State Properties of the Two-Dimensional t-J Model | cond-mat.str-el | The two-dimensional $t$-$J$ model in the ground state is investigated by the
power Lanczos method. The pairing-pairing correlation function for
$d_{x^2-y^2}$-wave symmetry is enhanced in the realistic parameter regime for
high-$T_c$ superconductors. The charge susceptibility $\chi_c$ shows divergent
behavior as $\chi_c... | physics |
6,919 | Fundamental Oscillation Periods of the Interlayer Exchange Coupling beyond the RKKY Approximation | cond-mat.str-el | A general method for obtaining the oscillation periods of the interlayer
exchange coupling is presented. It is shown that it is possible for the
coupling to oscillate with additional periods beyond the ones predicted by the
RKKY theory. The relation between the oscillation periods and the spacer Fermi
surface is clarif... | physics |
6,920 | Spin-Gap Proximity Effect Mechanism of High Temperature Superconductivity | cond-mat.str-el | When holes are doped into an antiferromagnetic insulator they form a slowly
fluctuating array of ``topological defects'' (metallic stripes) in which the
motion of the holes exhibits a self-organized quasi one-dimensional electronic
character. The accompanying lateral confinement of the intervening
Mott-insulating regio... | physics |
6,921 | Low temperature spin diffusion in the one-dimensional quantum $O(3)$ nonlinear $σ$-model | cond-mat.str-el | An effective, low temperature, classical model for spin transport in the
one-dimensional, gapped, quantum $O(3)$ non-linear $\sigma$-model is developed.
Its correlators are obtained by a mapping to a model solved earlier by Jepsen.
We obtain universal functions for the ballistic-to-diffusive crossover and the
value of ... | physics |
6,922 | Interlayer exchange coupling in Fe/Cr multilayers | cond-mat.str-el | We investigate the origin of the long period oscillation of the interlayer
exchange coupling in Fe/Cr trilayer systems. Within the stationary phase
approximation the periods of the oscillations are associated with extremal
vectors of the Fermi sphere of Cr. Using a realistic tight-binding model with
spin-orbit interact... | physics |
6,923 | Energy level statistics of the two-dimensional Hubbard model at low filling | cond-mat.str-el | The energy level statistics of the Hubbard model for $L \times L$ square
lattices (L=3,4,5,6) at low filling (four electrons) is studied numerically for
a wide range of the coupling strength. All known symmetries of the model
(space, spin and pseudospin symmetry) have been taken into account explicitly
from the beginni... | physics |
6,924 | Insulating gap in FeO: correlations and covalency | cond-mat.str-el | We report calculations of the electronic structure of FeO in the LDA and
LDA+U approximation with and without rhombohedral distortion. In both cases LDA
renders an antiferromagnetic metal, and LDA+U opens a Hubbard gap. However, the
character of the gap is qualitatively different in the two structure, and the
differenc... | physics |
6,925 | Effective actions for spin ladders | cond-mat.str-el | We derive a path-integral expression for the effective action in the
continuum limit of an AFM Heisenberg spin ladder with an arbitrary number of
legs. The map is onto an $O(3)$ nonlinear $\sigma$-model (NL$\sigma$M) with the
addition of a topological term that is effective only for odd-legged ladders
and half-odd inte... | physics |
6,926 | Thermodynamic Density Matrix renormalization Group Study of the Magnetic Susceptibility of Half-integer Quantum Spin Chains | cond-mat.str-el | It is shown that White's density matrix renormalization group technique can
be adapted to obtain thermodynamic quantities. As an illustration, the magnetic
susceptibility of Heisenberg S=1/2 and S=3/2 spin chains are computed. A
careful finite size analysis is made to determine the range of temperatures
where the resul... | physics |
6,927 | Magnetization plateaus in spin chains: ``Haldane gap'' for half-integer spins | cond-mat.str-el | We discuss zero-temperature quantum spin chains in a uniform magnetic field,
with axial symmetry. For integer or half-integer spin, $S$, the magnetization
curve can have plateaus and we argue that the magnetization per site $m$ is
topologically quantized as $q (S - m)= integer$ at the plateaus, where $q$ is
the period ... | physics |
6,928 | A New Phase Diagram for the t-J Model | cond-mat.str-el | We study the so-called nonmagnetic phases (dimer and flux states) in the t-J
model below half filling. We present a new phase diagram, at zero and finite
temperature, that includes broad areas of phase coexistence (dimer-flux or
flux-uniform), in accordance with experimental and numerical data on the
possibility of sep... | physics |
6,929 | Protracted Screening in the Periodic Anderson Model | cond-mat.str-el | The asymmetric infinite-dimensional periodic Anderson model is examined with
a quantum Monte Carlo simulation. For small conduction band filling, we find a
severe reduction in the Kondo scale, compared to the impurity value, as well as
protracted spin screening consistent with some recent controversial
photoemission ex... | physics |
6,930 | Antiferromagnetic Spin Ladders with Odd and Even number of Chains | cond-mat.str-el | We construct frustrated antiferromagnetic spin ladders with m chains for
which the exact ground state can be determined in a particular parameter
regime. The excitation spectrum is shown rigorously to be gapless ( with gap )
for odd ( even ) m. In a general parameter regime, the four-chain and periodic
ladders are stud... | physics |
6,931 | Fermi Surface of the 2D Hubbard Model at Weak Coupling | cond-mat.str-el | We calculate the interaction-induced deformation of the Fermi surface in the
two-dimensional Hubbard model within second order perturbation theory. Close to
half-filling, interactions enhance anisotropies of the Fermi surface, but they
never modify the topology of the Fermi surface in the weak coupling regime. | physics |
6,932 | Reflections on the One Dimensional Realization of Odd-Frequency Pairing | cond-mat.str-el | We discuss the odd-frequency pairing correlations discovered by Zachar,
Kivelson and Emery (ZKE) in a one dimensional Kondo lattice. A lattice model
that realizes the continuum theory of ZKE is introduced and the correlations it
gives rise to are identified as odd-frequency singlet pairing. The excitation
spectrum is f... | physics |
6,933 | Spectral Functions for the Holstein Model | cond-mat.str-el | We perform an unitary transformation for the symmetric phonon mode of the
Holstein molecular crystal hamiltonian. We show how to compute the electronic
spectral functions by exact numerical diagonalisation of an effective
hamiltonian fully taking account of the symmetric phonon mode, usually
discarded. | physics |
6,934 | Exact solution of a t-J chain with impurity | cond-mat.str-el | We study the effects of an integrable impurity in a periodic t-J chain. The
impurity couples to both spin and charge degrees of freedom and has the
interesting feature that the interaction with the bulk can be varied
continuously without losing integrability. We first consider ground state
properties close to half-fill... | physics |
6,935 | Spin excitations in the integrable open quantum group invariant supersymmetric t-J model | cond-mat.str-el | The integrable quantum group $spl_q(2,1)$-invariant supersymmetric t-J model
with open boundaries is studied via an analytic treatment of the Bethe
equations. An $su(2)$ feature is seen to hold for states at or close to
half-filling. For these states the eigenvalues of the transfer matrix of the
t-J model satisfy a set... | physics |
6,936 | The J_1-J_2 model revisited : Phenomenology of CuGeO_3 | cond-mat.str-el | We present a mean field solution of the antiferromagnetic Heisenberg chain
with nearest (J_1) and next to nearest neighbor (J_2) interactions. This
solution provides a way to estimate the effects of frustration. We calculate
the temperature-dependent spin-wave velocity, v_s(T) and discuss the
possibility to determine t... | physics |
6,937 | The Generalized Gutzwiller Method for n=>2 Correlated Orbitals: Itinerant Ferromagnetism in eg-bands | cond-mat.str-el | Using the generalized Gutzwiller method we present results on the
ferromagnetic behavior of extended Hubbard models with two degenerate eg
orbitals. We find significant differences to results obtained from Hartree-Fock
theory. | physics |
6,938 | The Generalized Gutzwiller Method for n=>2 Correlated Bands: First Order Metal-Insulator Transitions | cond-mat.str-el | We have generalized the Gutzwiller method to the cases of n=>2 correlated
bands and report studies on a degenerate two-band model with Hund's rule type
on-site interactions. At half band filling the metal-insulator transitions are
usually of first order. | physics |
6,939 | Integer filling metal insulator transitions in the degenerate Hubbard model | cond-mat.str-el | We obtain exact numerical solutions of the degenerate Hubbard model in the
limit of large dimensions (or large lattice connectivity). Successive
Mott-Hubbard metal insulator transitions at integer fillings occur at
intermediate values of the interaction and low enough temperature in the
paramagnetic phase. The results ... | physics |
6,940 | Substitution effects on spin fluctuations in the spin-Peierls compound CuGeO_3 | cond-mat.str-el | Using Raman scattering we studied the effect of substitutions on 1D spin
fluctuations in CuGeO_3 observed as a spinon continuum in frustration induced
exchange scattering. For temperatures below the spin-Peierls transition
(T_{SP}=14K) the intensity of this continuum at 120-500 cm^{-1} is
exponentially suppressed and t... | physics |
6,941 | Correlations in one-dimensional disordered electronic systems with interaction | cond-mat.str-el | We investigate the effects of randomness in a strongly correlated electron
model in one-dimension at half-filling. The ground state correlation functions
are exactly written by products of 3$\times$3 transfer matrices and are
evaluated numerically. The correlation lengths depend on randomness when the
interaction is ef... | physics |
6,942 | Organic Superconductors: Reduced Dimensionality and Correlation Effects | cond-mat.str-el | In this tutorial we will tackle the problem of electronic correlations in
quasi-one-dimensional organic superconductors. We will go through different
pieces of experimental evidence showing the range of applicability of the Fermi
and Luttinger liquid descriptions of the normal phase of the Bechgaard salts
series and th... | physics |
6,943 | Low Energy Properties of the (n,n) Carbon Nanotubes | cond-mat.str-el | According to band theory, an ideal undoped (n,n) carbon nanotube is metallic.
We show that the electron-electron interaction causes it to become Mott
insulating with a spin gap. More interestingly, upon doping it develops
superconducting fluctuations. | physics |
6,944 | Interplay between Heavy Fermions and Crystal Field Excitation in Kondo Lattices. Low-Temperature Thermodynamics and Inelastic Neutron Scattering Spectra of CeNiSn | cond-mat.str-el | The microscopic theory of interaction between the heavy fermions and the
crystal field excitations in Kondo lattices is presented. It is shown that the
heavy-fermion spectrum scaled by the Kondo temperature $T_K$ can be modified by
the crystal field excitations with the energy $\Delta_{CF}$ provided the
inequality $\De... | physics |
6,945 | Field-Induced Staggered Magnetic Order in La(2)NiO(4.133) | cond-mat.str-el | At low temperature the holes doped into the NiO(2) planes of La(2)NiO(4.133)
by the excess oxygen collect in diagonal stripes that separate narrow
antiferromagnetic domains. The magnetic order drops abruptly to zero at T_m =
110.5 K, but charge order remains with a period of 3a/2. We show that
application of a magnetic... | physics |
6,946 | Unified description of Fermi and non-Fermi liquid behavior in a conserving slave boson approximation for strongly correlated impurity models | cond-mat.str-el | We show that the presence of Fermi or non-Fermi liquid behavior in the SU(N)
x SU(M) Anderson impurity models may be read off the infrared threshold
exponents governing the spinon and holon dynamics in a slave boson
representation of these models. We construct a conserving T-matrix
approximation which recovers the exac... | physics |
6,947 | Electronic excitation spectra from ab-initio band structure results for LaMO_3 (M = Cr-Ni) | cond-mat.str-el | We present calculated electron excitation spectra for the LaMO_3 series
(M=Cr-Ni) obtained within ab-initio band structure calculations for the real
geometric and magnetic structures. The calculated results show good agreement
with the experimentally obtained spectra. This suggests that the transition
metal-transition ... | physics |
6,948 | Dramatic Switching of Magnetic Exchange in a Classic Transition Metal Oxide: Evidence for Orbital Ordering | cond-mat.str-el | Spin correlations in metallic and insulating phases of $V_2O_3$ and its
derivatives are investigated using magnetic neutron scattering. Metallic
samples have incommensurate spin correlations varying little with hole doping.
Paramagnetic insulating samples have spin correlations only among near
neighbors. The transition... | physics |
6,949 | Impact of Charge Ordering on Magnetic Correlations in Perovskite (Bi,Ca)MnO_3 | cond-mat.str-el | Single crystalline (Bi,Ca)MnO3 (74< %Ca <82) were studied with neutron
scattering, electron diffraction and bulk magnetic measurement. We discovered
dynamic ferromagnetic spin correlations at high temperatures, which are
replaced by antiferromagnetic spin fluctuations at a concomitant charge
ordering and structural tra... | physics |
6,950 | Gauge drag between half-filled Landau levels | cond-mat.str-el | The transresistance (i.e. the voltage induced in one layer by a current in
another) between composite fermions in double-layers of half-filled Landau
levels is shown to be dominated by scattering due to singular gauge field
fluctuations arising from the antisymmetric combination of density fluctuations
in two layers. T... | physics |
6,951 | Correlation Effects in Carbon Nanotubes | cond-mat.str-el | We consider the effects of Coulomb interactions on single-wall carbon
nanotubes using an on-site Hubbard interaction, u. For the (N,N) armchair tubes
the low energy theory is shown to be identical to a 2-chain Hubbard model at
half-filling, with an effective interaction u_N = u/N. Umklapp scattering leads
to gaps in th... | physics |
6,952 | Weakly Coupled Antiferromagnetic Quantum Spin Chains | cond-mat.str-el | Quasi-one-dimensional quantum antiferromagnets formed by a d-dimensional
hypercubic lattice of weakly coupled spin-1/2 antiferromagnetic Heisenberg
chains are studied by combining exact results in one-dimension and
renormalization group analyses of the interchain correlations. It is shown that
d-dimensional magnetic lo... | physics |
6,953 | Two routes to metallic behavior for a Kondo insulator | cond-mat.str-el | Cold neutron spectroscopy was performed on CeNi_{1-x}Cu_xSn to investigate
how the magnetic gap in the 'Kondo insulator' CeNiSn is destroyed by
temperature (T), chemical substitution (x), and external magnetic field. Upon
doping, the spin gap collapses and magnetic Bragg peaks occur initially (x =
0.13) at the commensu... | physics |
6,954 | The Quantum O(N) Heisenberg Antiferromagnet for N -> infinityy | cond-mat.str-el | We study the O(N) quantum Heisenberg antiferromagnet using a parametrisation
in terms of real fermions. The N->infinity limit of the model is controlled by
a saddle point that is infinitely degenerate in many cases and which represents
singlet states on dimers that cover the lattice. Our results are similar to
results ... | physics |
6,955 | Magnetic phase diagram and transport properties of FeGe_2 | cond-mat.str-el | We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an ... | physics |
6,956 | Luttinger Stripes in Antiferromagnets | cond-mat.str-el | We propose a model for the physics of stripes in antiferromagnets in which
the stripes are described by Luttinger liquids hybridized with
antiferromagnetic domains. Using bosonization techniques we study the model in
the limit where the magnetic correlation length is larger than the inter-stripe
distance and propose an... | physics |
6,957 | Collective Kondo effect in the Anderson-Hubbard lattice | cond-mat.str-el | The periodic Anderson model is extended by switching on a Hubbard U for the
conduction electrons. We use the Gutzwiller variational method to study the
nearly integral valent limit. The lattice Kondo energy contains the U-dependent
chemical potential of the Hubbard subsystem in the exponent, and the
correlation-induced... | physics |
6,958 | Sr impurity effects on the magnetic correlations of LaSrCuO | cond-mat.str-el | We examine the low-temperature magnetic properties of moderately doped
LaSrCuO paying particular attention to the spin-glass (SG) phase and the C-IC
transition as they are affected by Sr impurity disorder. New measurements of
the low-temperature susceptibility in the SG phase show an increase of an
anomalously small Cu... | physics |
6,959 | Phenomenological theory of two-dimensional quantum liquids | cond-mat.str-el | A phenomenological theory is presented for two-dimensional quantum liquids in
terms of the Fermi surface geometry. It is shown that there is a one-to-one
correspondence between the properties of an interacting electron system and its
corresponding Fermi surface. By doing this, the concept of Fermi surface is
generalize... | physics |
6,960 | Period doubling in the 2D Antiferromagnet. New gauge-fields and their anomalies | cond-mat.str-el | We construct an effective gauge field theory model describing a 2D quantum
antiferromagnet in the flux phase ground state. Due to period doubling the
number of gauge fields is four rather than the naively expected single one.
These additional gauge fields correspond to field configurations in which the
flux is staggere... | physics |
6,961 | Spectral Functions of One-dimensional Models of Correlated Electrons | cond-mat.str-el | Using the Ogata-Shiba wave function, the spectral functions of the
one-dimensional infinite U Hubbard model are calculated for various
concentrations. It is shown that the ``shadow band'' feature due to 2k_F
fluctuations becomes more intense close to half-filling. Comparing these
results with exact diagonalization data... | physics |
6,962 | Dynamics of the Hubbard model: a general approach by time dependent variational principle | cond-mat.str-el | We describe the quantum dynamics of the Hubbard model at semi-classical
level, by implementing the Time-Dependent Variational Principle (TDVP)
procedure on appropriate macroscopic wavefunctions constructed in terms of
su(2)-coherent states. Within the TDVP procedure, such states turn out to
include a time-dependent qua... | physics |
6,963 | Electron Green's Function in the Planar t-J Model | cond-mat.str-el | The electron Green's functions $G({\bf k},\omega)$ within the t-J model and
in the regime of intermediate doping is studied analytically using equations of
motion for projected fermionic operators and the decoupling of the self energy
into the single-particle and spin fluctuations. It is shown that the assumption
of ma... | physics |
6,964 | Spin dynamics of dimerized Heisenberg chains | cond-mat.str-el | We study numerically the dimerized Heisenberg model with frustration
appropriate for the quasi-1D spin-Peierls compound CuGeO$_3$. We present
evidence for a bound state in the dynamical structure factor for any finite
dimerization $\delta$ and estimate the respective spectral weight. For the
homogeneous case ($\delta=0... | physics |
6,965 | Abelian bosonization approach to quantum impurity problems | cond-mat.str-el | Using Abelian Bosonization, we develop a simple and powerful method to
calculate the correlation functions of the two channel Kondo model and its
variants. The method can also be used to identify all the possible boundary
fixed points and their maximum symmetry, to calculate straightforwardly the
finite size spectra, t... | physics |
6,966 | Phase String Effect in the t-J Model: General Theory | cond-mat.str-el | We reexamine the problem of a hole moving in an antiferromagnetic spin
background and find that the injected hole will always pick up a sequence of
nontrivial phases from the spin degrees of freedom. Previously unnoticed, such
a string-like phase originates from the hidden Marshall signs which are
scrambled by the hopp... | physics |
6,967 | Antiferromagnetic systems with spin gap: exact results | cond-mat.str-el | We describe some antiferromagnetic systems which exhibit spin gaps. We also
discuss the effect of doping one such system, namely, the spin-ladders, with
holes. Some model antiferromagnetic systems with spin gap are reviewed for
which exact results are available. Exact results for a doped spin-ladder model
are also ment... | physics |
6,968 | Infrared spectroscopic study of phonons coupled to charge excitations in FeSi | cond-mat.str-el | From an investigation of the optical conductivity of FeSi single crystals
using FTIR spectroscopy in the frequency range from 30 to 20000 wavenumbers we
conclude that the transverse effective charge of the Fe and Si ions is
approximately 4e. Of the five optical phonons which are allowed by symmetry we
observe only four... | physics |
6,969 | Charge Localization in Disordered Colossal-Magnetoresistance Manganites | cond-mat.str-el | The metallic or insulating nature of the paramagnetic phase of the
colossal-magnetoresistance manganites is investigated via a double exchange
Hamiltonian with diagonal disorder. Mobility edge trajectory is determined with
the transfer matrix method. Density of states calculations indicate that random
hopping alone is ... | physics |
6,970 | DMRG study of ferromagnetism in a one-dimensional Hubbard model | cond-mat.str-el | The one dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping has been studied with the density-matrix renormalization
group (DMRG) method. A large region of ferromagnetism has been found for finite
density and finite on-site interaction. | physics |
6,971 | Comment on ``Integrability and Coherence of Hopping between 1D Correlated Electron Systems'' | cond-mat.str-el | We comment on recent numerical studies concerning coupled 1D electron liquids
(F. Mila and D. Poilblanc, Phys. Rev. Lett. 76, 287 (1996)). In particular, we
point out that the importance of integrability observed in the results of these
authors for the quantity $P(t)$ is really an indication of the importance of
integr... | physics |
6,972 | A scenario for the electronic state in the manganase perovskites: the orbital correlated metal | cond-mat.str-el | We argue that, at low temperatures and well into the ferromagnetic phase, the
physics of the manganase perovskites may be characterized by a correlated
metallic state near a metal insulator transition where the orbital degrees of
freedom play a main role. This follows from the observation that a two-band
degenerate Hub... | physics |
6,973 | Band ferromagnetism versus collective Kondo state in lattice fermion models | cond-mat.str-el | It is becoming widely recognized that, contrary to earlier expectations, the
usual one-band Hubbard model does not give an explanation for itinerant
ferromagnetism. After reviewing the status of magnetic ordering in the one-band
model, we discuss the possibility of ferromagnetism in some recently introduced
two-band Hu... | physics |
6,974 | Uncertainty Principle Enhanced Pairing Correlations in Projected Fermi Systems Near Half Filling | cond-mat.str-el | We point out the curious phenomenon of order by projection in a class of
lattice Fermi systems near half filling. Enhanced pairing correlations of
extended s-wave Cooper pairs result from the process of projecting out s-wave
Cooper pairs, with negligible effect on the ground state energy. The Hubbard
model is a particu... | physics |
6,975 | Magnon-magnon interactions in the Spin-Peierls compound CuGeO_3 | cond-mat.str-el | In a magnetic substance the gap in the Raman spectrum, Delta_R, is
approximatively twice the value of the neutron scattering gap, Delta_S, if the
the magnetic excitations (magnons) are only weakly interacting.
But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is
approximatively 1.49-1.78, indicating a... | physics |
6,976 | Competition between Hund-Rule Coupling and Kondo Effect | cond-mat.str-el | We investigate a problem about the competition between the hybridization and
the Hund-rule coupling by applying the Wilson numerical renormalization-group
method to the extended Kondo model where the impurity spin interacts via the
Hund-rule coupling, with an extra spin which is isolated from the conduction
electrons. ... | physics |
6,977 | Pseudoparticle Description of the 1D Hubbard Model Electronic Transport Properties | cond-mat.str-el | We extend the pseudoparticle transport description of the Hubbard chain to
all energy scales. In particular we compute the mean value of the electric
current transported by any Bethe-ansatz state and the transport masses of the
charge carriers. We present numerical results for the optical conductivity of
the model at h... | physics |
6,978 | Specific Heat of the 2D Hubbard Model | cond-mat.str-el | Quantum Monte Carlo results for the specific heat c of the two dimensional
Hubbard model are presented. At half-filling it was observed that $c \sim T^2$
at very low temperatures. Two distinct features were also identified: a low
temperature peak related to the spin degrees of freedom and a higher
temperature broad pea... | physics |
6,979 | Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy | cond-mat.str-el | A slave-boson functional-integral method has been developed for the Hubbard
model with arbitrary, orbital degeneracy $D$. Its saddle-point mean-field
theory is equivalent to the Gutzwiller approximation, as in the case of
single-band Hubbard model. Our theory is applied to the doubly degenerate ($D =
2$) model, and num... | physics |
6,980 | Interplay of Mott Transition and Ferromagnetism in the Orbitally Degenerate Hubbard Model | cond-mat.str-el | A slave boson representation for the degenerate Hubbard model is introduced.
The location of the metal to insulator transition that occurs at commensurate
densities is shown to depend weakly on the band degeneracy M. The relative
weights of the Hubbard sub-bands depend strongly on M, as well as the magnetic
properties.... | physics |
6,981 | Self-consistent perturbational study of insulator-to-metal transition in Kondo insulators due to strong magnetic field | cond-mat.str-el | In order to study the effects of strong magnetic field on Kondo insulators,
we calculate magnetization curves and single-particle excitation spectra of the
periodic Anderson model at half-filling under finite magnetic field by using
the self-consistent second-order perturbation theory combined with the local
approximat... | physics |
6,982 | Spectral properties of the 2D Holstein t-J model | cond-mat.str-el | Employing the Lanczos algorithm in combination with a kernel polynomial
moment expansion (KPM) and the maximum entropy method (MEM), we show a way of
calculating charge and spin excitations in the Holstein t-J model, including
the full quantum nature of phonons. To analyze polaron band formation we
evaluate the hole sp... | physics |
6,983 | On the stability of polaronic superlattices in strongly coupled electron-phonon systems | cond-mat.str-el | We investigate the interplay of electron-phonon (EP) coupling and strong
electronic correlations in the frame of the two-dimensional (2D) Holstein t-J
model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled
band case. The use of direct Lanczos diagonalization on finite lattices allows
us to includ... | physics |
6,984 | Spin polarons in the t-J model in an unconstrained representation | cond-mat.str-el | The report discusses the slave-fermion representations of the t-J model and
describes another representation, in which fermions and bosons are completely
commuting and in which the properties of fermions are directly related to the
properties of physical holes. For a study of the system in the new
representation at hal... | physics |
6,985 | Indirect RKKY interaction in any dimensionality | cond-mat.str-el | We present an analytical method which enables one to find the exact spatial
dependence of the indirect RKKY interaction between the localized moments via
the conduction electrons for the arbitrary dimensionality $n$. The
corresponding momentum dependence of the Lindhard function is exactly found for
any $n$ as well. De... | physics |
6,986 | Comment on ``Impurity states and the absence of quasiparticle localization in disordered d-wave superconductors'' | cond-mat.str-el | In a recent Letter Balatsky and Salkola made their conclusion about the
absence of localization in disordered d-wave superconductors exploiting the
idea that strongly overlapping impurity states formed a network capable to
provide the transport. We present here the correct estimate of hopping matrix
elements between tw... | physics |
6,987 | Is a doped 'Kondo' insulator different from doped Silicon? | cond-mat.str-el | We have observed the metal-insulator transition in the strongly correlated
insulator FeSi with the chemical substitution of Al at the Si site. The
magnetic susceptibility, heat capacity, and field dependent conductivity are
measured for Al concentrations ranging from 0 to 0.08. For concentrations
greater than 0.01 we f... | physics |
6,988 | Crossover between Luttinger and Fermi liquid behavior in weakly coupled metallic chains | cond-mat.str-el | We use higher-dimensional bosonization to study the normal state of electrons
in weakly coupled metallic chains interacting with long-range Coulomb forces.
Particular attention is paid to the crossover between Luttinger and Fermi
liquid behavior as the interchain hopping is varied. Although in the physically
interestin... | physics |
6,989 | A Model for the Occurrence of Lock-ins in Holmium in c-axis Magnetic Fields | cond-mat.str-el | We introduce a novel interpretation of the sequence of commensurate lock-ins
of the spiral wave vector, tau, observed in the helimagnetic phase of holmium
in the presence of c-axis magnetic fields. This is the first successful model
for the prediction of these lock-ins. We show that a model which combines a
spin-slip m... | physics |
6,990 | Conductance of a quantum wire: Landauer's approach versus Kubo formula | cond-mat.str-el | The transport in a pure one-dimensional quantum wire is investigated for any
range of interactions. First, the wire is connected to measuring leads. The
transmission of an incident electron is found to be perfect, and the
conductance is not renormalized by the interactions. Either Landauer's approach
or Kubo formula ca... | physics |
6,991 | On the origin of the quantum-critical transition in the bilayer Heisenberg model | cond-mat.str-el | The bilayer Heisenberg antiferromagnet is known to exhibit a quantum-critical
transition at a particular value of the inter-layer coupling. Using a new type
of coherent state, appropriate to the special order parameter structure of the
bilayer, we map the problem onto the quantum non-linear sigma model. It is
found tha... | physics |
6,992 | Spectral functions of the 1D Hubbard model in the U -> \infty limit: How to use the factorized wave-function | cond-mat.str-el | We give the details of the calculation of the spectral functions of the 1D
Hubbard model using the spin-charge factorized wave-function for several
versions of the U -> +\infty limit. The spectral functions are expressed as a
convolution of charge and spin dynamical correlation functions. A procedure to
evaluate these ... | physics |
6,993 | Dynamics of the spin-half Heisenberg chain at intermediate temperatures | cond-mat.str-el | Combining high-temperature expansions with the recursion method and quantum
Monte Carlo simulations with the maximum entropy method, we study the dynamics
of the spin-1/2 Heisenberg chain at temperatures above and below the coupling
J. By comparing the two sets of calculations, their relative strengths are
assessed. At... | physics |
6,994 | Exact ground and excited states of frustrated antiferromagnets on the CaV_4O_9 lattice | cond-mat.str-el | The experimental observation of a spin-gap in the antiferromagnetic spin-1/2
compound $CaV_4O_9$ has been attributed to the formation of a plaquette
resonating-valence-bond (PRVB) state in the underlying 1/5-depleted square
lattice. We construct a spin-1/2 model on the 1/5-depleted lattice for which
the PRVB state can ... | physics |
6,995 | Single particle excitations of the Kondo lattice | cond-mat.str-el | We present a simple theory for the description of the single particle
excitations in the Kondo lattice model. Thereby we derive an `effective
Hamiltonian' which describes the coherent propagation of single particle-like
fluctuations on a strong coupling background. Even for f-electrons which are
replaced by Kondo-spins... | physics |
6,996 | Perturbation Theory around Non-Nested Fermi Surfaces II. Regularity of the Moving Fermi Surface: RPA contributions | cond-mat.str-el | Regularity of the deformation of the Fermi surface under short-range
interactions is established for all contributions to the RPA self-energy (it is
proven in an accompanying paper that the RPA graphs are the least regular
contributions to the self-energy). Roughly speaking, the graphs contributing to
the RPA self-ener... | physics |
6,997 | Hole Doping Evolution of the Quasiparticle Band in Models of Strongly Correlated Electrons for the High-T_c Cuprates | cond-mat.str-el | Quantum Monte Carlo (QMC) and Maximum Entropy (ME) techniques are used to
study the spectral function $A({\bf p},\omega)$ of the one band Hubbard model
in strong coupling including a next-nearest-neighbor electronic hopping with
amplitude $t'/t= -0.35$. These values of parameters are chosen to improve the
comparison of... | physics |
6,998 | Reduction of ordered moment and Neel temperature of quasi one-dimensional antiferromagnets Sr2CuO3 and Ca2CuO3 | cond-mat.str-el | We report elastic neutron diffraction and muon spin relaxation (muSR)
measurements of the quasi one-dimensional antiferromagnets Sr2CuO3 and Ca2CuO3,
which have extraordinarily reduced TN/J ratios. We observe almost
resolution-limited antiferromagnetic Bragg reflections in Sr2CuO3 and obtain a
reduced ordered moment si... | physics |
6,999 | Can Majorana Fermions correctly describe the ordered state of an antiferromagnetic Heisenberg chain? | cond-mat.str-el | To check the reliability of the Majorana representation of quantum spin
systems, we use it to compute the ground state energy of an antiferromagnetic
spin 1/2 chain to one loop order. We find a very small one loop correction of
the mean field energy and a discrepancy of >100% compared to the Bethe Ansatz
result. We con... | physics |
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