publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
1999-08-27 | Spontaneous emission of phonons by coupled quantum dots | We find an interference effect for electron-phonon interactions in coupled
semiconductor quantum dots that can dominate the nonlinear transport properties
even for temperatures close to zero. The intradot electron tunnel process leads
to a `shake up' of the phonon system and is dominated by a double-slit-like
interfere... | 9908397v1 |
1999-08-28 | Quantum Measurement Operations with Nanomagnets and SQUIDs | The low-energy behaviour of 2 coupled nanomagnets or 2 coupled SQUIDs,
interacting with their environment, can be described by the model of a ``Pair
or Interacting Spins Coupled to an Environmental Sea'' (PISCES). These physical
systems can then be used for a measurement operation in which system, apparatus
and environ... | 9908424v1 |
1999-09-14 | Selection Rule in Josephson Coupling between In and Sr2RuO4 | We have studied the Josephson coupling between a conventional s-wave
superconductor (In) and Sr2RuO4 and found that the coupling is allowed in the
in-plane direction, but not along the c axis. This selection rule indicates
that the symmetry of superconducting order parameter of Sr2RuO4 is either p- or
alternatively, pu... | 9909214v1 |
1999-09-14 | Coupled phonon-ripplon modes in a single wire of electrons on the liquid-helium surface | The coupled phonon-ripplon modes of the quasi-one-dimensional electron chain
on the liquid helium sutface are studied. It is shown that the electron-ripplon
coupling leads to the splitting of the collective modes of the wire with the
appearance of low-frequency modes and high-frequency optical modes starting
from thres... | 9909216v1 |
1999-09-28 | Enhancement of Stochastic Resonance in distributed systems due to a selective coupling | Recent massive numerical simulations have shown that the response of a
"stochastic resonator" is enhanced as a consequence of spatial coupling.
Similar results have been analytically obtained in a reaction-diffusion model,
using "nonequilibrium potential" techniques. We now consider a field-dependent
diffusivity and sh... | 9909397v1 |
1999-09-30 | Enhancement of Josephson quasiparticle current in coupled superconducting single-electron transistors | The Josephson quasiparticle (JQP) cycle in a voltage-biased superconducting
single-electron transistor (SSET) combines coherent Cooper pair tunneling with
incoherent quasiparticle decay. We have measured the influence of current flow
through an independently-biased SSET on the JQP cycle when the two SSET's have
a stron... | 9909442v1 |
1999-10-05 | Vortices in magnetically coupled superconducting layered systems | Pancake vortices in stacks of thin superconducting films or layers are
considered. It is stressed that in the absence of Josephson coupling
topological restrictions upon possible configurations of vortices are removed
and various examples of structures forbidden in bulk superconductors are given.
In particular, it is s... | 9910063v2 |
1999-10-21 | Quasi-particle characteristics of the one-dimensional polaron | The main quasi-particle characteristics of the one-dimensional polaron are
estimated within and beyond the most general Gaussian approximation at
arbitrary electron-phonon coupling. We have derived explicitly the ground-state
energy and the effective mass in the weak- and strong-coupling regimes. For
arbitrary coupling... | 9910327v1 |
1999-11-03 | Non equilibrium mode coupling theory for supercooled liquids and glasses | A formally exact set of equations is derived for the description of
nonequilibrium phenomena in classical liquids and glasses. With the help of a
non equilibrium projection operator formalism, the correlation functions and
fluctuation propagators are expressed in terms of memory functions and time
dependent collective ... | 9911025v1 |
1999-11-23 | Phase transition in the transverse Ising model using the extended coupled-cluster method | The phase transition present in the linear-chain and square-lattice cases of
the transverse Ising model is examined. The extended coupled cluster method
(ECCM) can describe both sides of the phase transition with a unified approach.
The correlation length and the excitation energy are determined. We demonstrate
the abi... | 9911365v1 |
1999-12-25 | Phonon mediated hole pairing in the 1D Hubbard model near half-filling | The Hamiltonian describing a system of strongly correlated electrons coupled
to dispersionless phonons was solved numerically for a ring of 8 atoms using
the density matrix renormalization group (DMRG) method. It was found that
electron correlation and electron-phonon coupling compete against each other,
and strong ele... | 9912449v2 |
2000-01-25 | Duality relations for M coupled Potts models | We establish explicit duality transformations for systems of M q-state Potts
models coupled through their local energy density, generalising known results
for M=1,2,3. The M-dimensional space of coupling constants contains a selfdual
sub-manifold of dimension D_M = [M/2].
For the case M=4, the variation of the effect... | 0001367v2 |
2000-02-03 | Magnetism and superconductivity in underscreened Kondo chains | We present a one dimensional model of electrons coupled to localized moments
of spin $S\ge 1$ in which magnetism and superconductivity interplay in a
nontrivial manner. This model has a non-Fermi liquid ground state of the chiral
spin liquid type. A non-conventional odd-frequency pairing is shown to be the
dominant ins... | 0002061v1 |
2000-02-28 | Electronic transport through a local state linearly coupled to phonon modes | A resolvent formalism is applied to the problem of inelastic scattering of an
electron linearly coupled to a set of phonon modes. It is shown how the many
phonon mode coupling and excitation can be reduced to a single phonon mode
description, consistent with other approaches to the phenomenon of inelastic
tunneling in ... | 0002425v2 |
2000-03-10 | Structures and propagation in globally coupled systems with time delays | We consider an ensemble of globally coupled phase oscillators whose
interaction is transmitted at finite speed. This introduces time delays, which
make the spatial coordinates relevant in spite of the infinite range of the
interaction. We show that one-dimensional arrays synchronize in an asymptotic
state where all the... | 0003174v1 |
2000-03-23 | Magnetic Properties of HTSC with a Weak Interlayer Coupling | Magnetic properties of layered high temperature superconductors with a weak
interlayer coupling in the region of the critical fluctuations are investigated
in the framework of the Ginzburg--Landau approach. The sample magnetization is
calculated within a perturbative approach to the second order in the interlayer
coupl... | 0003376v4 |
2000-03-30 | Observation of harmonic generation and nonlinear coupling in the collective dynamics of a Bose condensate | We report the observation of harmonic generation and strong nonlinear
coupling of two collective modes of a condensed gas of rubidium atoms. Using a
modified TOP trap we changed the trap anisotropy to a value where the frequency
of the m=0 high-lying mode corresponds to twice the frequency of the m=0
low-lying mode, th... | 0003495v1 |
2000-04-13 | Oscillatory Exchange Coupling and Positive Magnetoresistance in Epitaxial Oxide Heterostructures | Oscillations in the exchange coupling between ferromagnetic
$La_{2/3}Ba_{1/3}MnO_3$ layers with paramagnetic $LaNiO_3$ spacer layer
thickness has been observed in epitaxial heterostructures of the two oxides.
This behavior is explained within the RKKY model employing an {\it ab initio}
calculated band structure of $LaN... | 0004230v1 |
2000-05-08 | Electronic states in correlated three-coupled chains | Three-coupled chains of quarter-filled Hubbard model with dimerization have
been studied for periodic boundary conditions. By use of a renormalization
group method, it is found that the interchain hopping is renormalized to zero
leading to confinement when charge gap becomes larger than the effective
interchain hopping... | 0005138v1 |
2000-05-24 | Effects of Boson Dispersion in Fermion-Boson Coupled Systems | We study the nonlinear feedback in a fermion-boson system using an extension
of dynamical mean-field theory and the quantum Monte Carlo method. In the
perturbative regimes (weak-coupling and atomic limits) the effective
interaction among fermions increases as the width of the boson dispersion
increases. In the strong c... | 0005395v1 |
2000-07-17 | Finite-wavevector phonon coupling to degenerate electronic states in LaSrCuO | We consider finite-k electron-phonon coupling appropriate for a
superconductor with a very short coherence length and local intersite pairs.
From group theoretical analyis we find that phonons with nonzero k can couple
to degenerate electronic states in LaSrCuO and a Jahn-Teller-like distortion is
found to be operati... | 0007284v1 |
2000-08-03 | Coherent population transfer in coupled semiconductor quantum dots | We propose a solid-state implementation of stimulated Raman adiabatic passage
in two coupled semiconductor quantum dots. Proper combination of two pulsed
laser fields allows the coherent carrier transfer between the two
nanostructures without suffering significant losses due to environment
coupling. By use of a general... | 0008058v1 |
2000-08-16 | Flow equation analysis of the anisotropic Kondo model | We use the new method of infinitesimal unitary transformations to calculate
zero temperature correlation functions in the strong-coupling phase of the
anisotropic Kondo model. We find the dynamics on all energy scales including
the crossover behaviour from weak to strong coupling. The integrable structure
of the Hamilt... | 0008242v1 |
2000-08-19 | Phase synchronization and noise-induced resonance in systems of coupled oscillators | We study synchronization and noise-induced resonance phenomena in systems of
globally coupled oscillators, each possessing finite inertia. The behavior of
the order parameter, which measures collective synchronization of the system,
is investigated as the noise level and the coupling strength are varied, and
hysteretic... | 0008288v1 |
2000-08-29 | Effects of interladder couplings in the trellis lattice | Strongly correlated models on coupled ladders in the presence of frustration,
in particular the trellis lattice, are studied by numerical techniques. For the
undoped case, the possibility of incommensurate peaks in the magnetic structure
factor at low temperatures is suggested. In the doped case, our main conclusion
fo... | 0008427v2 |
2000-09-14 | Distance-depending electron-phonon interactions from one- and two-body electronic terms in a dimer | For a dimer with a non-degenerate orbital built from atomic wave functions of
Gaussian shape we evaluate all the electron-phonon couplings derived from the
one-body and two-body electronic interactions, considering both the adiabatic
and extreme non-adiabatic limit. Not only the values of the coupling parameters
in the... | 0009215v1 |
2000-10-05 | Thermodynamics of Crossover from Weak- to Strong-Coupling Superconductivity | In this paper we study an evolution of low-temperature thermodynamical
quantities for an electron gas with a $ \delta $-function attraction as the
system crosses over from weak-coupling (BCS-type) to strong-coupling
(Bose-type) superconductivity in three and two dimensions. | 0010085v2 |
2000-10-26 | Upper critical dimension, dynamic exponent and scaling functions in the mode-coupling theory for the Kardar-Parisi-Zhang equation | We study the mode-coupling approximation for the KPZ equation in the strong
coupling regime. By constructing an ansatz consistent with the asymptotic forms
of the correlation and response functions we determine the upper critical
dimension d_c=4, and the expansion z=2-(d-4)/4+O((4-d)^2) around d_c. We find
the exact z=... | 0010410v1 |
2000-11-09 | Superposition of photon- and phonon- assisted tunneling in coupled quantum dots | We report on electron transport through an artificial molecule formed by two
tunnel coupled quantum dots, which are laterally confined in a two-dimensional
electron system of an Al$_x$Ga$_{1-x}$As/GaAs heterostructure. Coherent
molecular states in the coupled dots are probed by photon-assisted tunneling
(PAT). Above 10... | 0011155v2 |
2000-11-12 | Josephson Coupling through a Quantum Dot | We derive, via fourth order perturbation theory, an expression for the
Josephson current through a gated interacting quantum dot. We analyze our
expression for two different models of the superconductor-dot-superconductor
(SDS) system. When the matrix elements connecting dot and leads are featureless
constants, we comp... | 0011201v1 |
2000-12-01 | Is the quantum dot at large bias a weak-coupling problem? | We examine the two-lead Kondo model for a d.c. biased quantum dot in the
Coulomb blockade regime. From perturbative calculations of the magnetic
susceptibility, we show that the problem retains its strong-coupling nature,
even at bias voltages larger than the equilibrium Kondo temperature. We give a
speculative discuss... | 0012005v3 |
2000-12-06 | Raman Scattering from Magnetic Excitations in coupled Spin Ladders | We consider Raman scattering of coupled two leg spin ladders in the
Fleury-Loudon regime. We derive the dependence of the intensity with
polarization of the incoming light and temperature and discuss the effect of
interaction of the elementary excitations on the shape of the spectrum. We show
that Raman scattering spec... | 0012069v1 |
2000-12-26 | The polaron confined in one dimension | The ground-state energy, the effective mass and the number of virtual phonons
of the optical large polaron confined strictly in one dimension have been
estimated by using the generalized Gaussian approximation. The leading-order
terms take care of all Gaussian fluctuations in the system and improve the
conventional var... | 0012467v1 |
2001-01-08 | Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange coupling | A theoretical study of the magnetization curves of quasiperiodic magnetic
multilayers is presented. We consider structures composed by ferromagnetic
films (Fe) with interfilm exchange coupling provided by intervening
nonferromagnetic layers (Cr). The theory is based on a realistic
phenomenological model, which includes... | 0101099v1 |
2001-01-09 | Effect of couplings weakening and reversing in ferromagnetic Ising systems - Rigorous inequalities | We consider Ising systems where all the many-spin couplings $J_A$ are
positive. We show that the absolute value of all the many-spin correlations
does not increase when the value of any of the couplings is reduced, taking any
value in the interval $[-J_A,J_A]$. Results of this type are motivated by work
in systems such... | 0101110v1 |
2001-02-11 | Antiferromagnetic Interlayer Coupling in Ferromagnetic Semiconductor EuS/PbS(001) Superlattices | Antiferromagnetic coupling between ferromagnetic layers has been observed for
the first time in all-semiconductor superlattice structure EuS/PbS(001), by
neutron scattering and magnetization measurements. Spin-dependent superlattice
band structure effects are invoked to explain the possible origin and the
strength of t... | 0102194v2 |
2001-02-23 | Heat Capacity of MgB_2: Evidence for Moderately Strong Coupling Behavior | We characterize the superconducting state of phase pure polycrystalline
samples of the new layered superconductor MgB$_2$ by specific heat measurements
in magnetic fields up to 9 T. The characteristic jump at the superconducting
transition is observed and compared with the predictions of weak coupling
BCS-theory and th... | 0102432v2 |
2001-03-16 | Renormalization Group study of the Sliding Luttinger liquids | We derive the RG-flow equations of the sliding Luttinger liquid perturbed by
charge-density-wave (CDW) and superconducting (SC) operators. Using them we
study the phase diagram of an array of XXZ spin chains coupled by Ising terms.
In the weak coupling regime we find a new class of non-gaussian and unstable
fixed point... | 0103356v3 |
2001-04-02 | Dielectric properties of correlated quantum plasmas | Results for the dynamic structure factor of a one-component plasma are
presented for the situations of strong coupling and weak degeneracy and strong
degeneracy and weak coupling. Possibilities to obtain rigorous results when
both, coupling and degeneracy are large are discussed. | 0104030v1 |
2001-04-23 | High-Tc via electron polar coupling: relation to low-Tc superconductivity and to chiral symmetry in particle physics | Directional coupling of Thornber-Feynman polarization with the high-Tc ARPES
distribution specifies the optimum flatband pseudogap \Delta and mobile
localized quasiparticle. This coupling peaks by tuning the statistics and
interaction energy to produce stable short-ranged directional pairing that
reflects the lattice a... | 0104443v1 |
2001-04-24 | Anticorrelations, subbrownian stochastic drift, and 1/f-like spectra in stable financial systems | Statistic dynamics of financial systems is investigated, basing on a model of
randomly coupled equation system driven by stochastic Langevin force. It is
found that in stable regime the noise power spectrum of the system is of
1/f^alpha form, with the exponent alpha=3/2 in case of Hermitian coupling
matrices, or slight... | 0104456v1 |
2001-05-02 | Collective dynamics of two-mode stochastic oscillators | We study a system of two-mode stochastic oscillators coupled through their
collective output. As a function of a relevant parameter four qualitatively
distinct regimes of collective behavior are observed. In an extended region of
the parameter space the periodicity of the collective output is enhanced by the
considered... | 0105046v1 |
2001-06-05 | Synchronization in the non-extensive Kuramoto model | We study the onset of synchronization in square lattices of limit cycle
oscillators with long-range coupling by means of numerical simulations of the
Kuramoto model. In this regime the critical coupling strength depends on the
system size and interaction range reflecting the non extensive behavior of the
system, but an... | 0106093v1 |
2001-06-15 | Real-Space Renormalization Group Study of Effects of Anisotropy on S=1 Random Antiferromagnetic Chain | We investigate S=1 antiferromagnetic quantum spin chain, whose exchange
couplings are strongly disordered. By the real-space renomalization group
method, introduced by Ma, Dasgupta, and Hu, the renormalization group flows are
analyzed numerically in a plain of the anisotoropy of the exchange coupling vs.
the staggered ... | 0106289v2 |
2001-07-04 | Electronic conduction in multi-walled carbon nanotubes: Role of intershell coupling and incommensurability | Geometry incommensurability between weakly coupled shells in multi-walled
carbon nanotubes is shown to be the origin of unconventional electronic
conduction mechanism, power-law scaling of the conductance, and remarkable
magnetotransport and low temperature dependent conductivity when the dephasing
mechanism is dominat... | 0107084v1 |
2001-07-05 | Scattering theory on graphs | We consider the scattering theory for the Schr\"odinger operator
$-\Dc_x^2+V(x)$ on graphs made of one-dimensional wires connected to external
leads. We derive two expressions for the scattering matrix on arbitrary graphs.
One involves matrices that couple arcs (oriented bonds), the other involves
matrices that couple ... | 0107104v1 |
2001-07-18 | Spin-orbit coupling effects on quantum transport in lateral semiconductor dots | The effects of interplay between spin-orbit coupling and Zeeman splitting on
weak localisation and universal conductance fluctuations in lateral
semiconductor quantum dots are analysed: All possible symmetry classes of
corresponding random matrix theories are listed and crossovers between them
achievable by sweeping ma... | 0107385v1 |
2001-08-06 | Superconducting Fluctuations in Granular Metals with a Large Coupling Between the Grains | We study the fluctuation conductivity of superconducting granular metals at
low temperatures and strong magnetic field destroying the Cooper pairs.
Explicit calculations are performed for larger values of the coupling between
the grains than those considered in previous works. We show that in a broad
region of the coup... | 0108104v3 |
2001-08-07 | Fictitious fluxes in doped antiferromagnets | In a tight binding model of charged spin-1/2 electrons on a square lattice, a
fully polarized ferromagnetic spin configuration generates an apparent U(1)
flux given by $2\pi$ times the skyrmion charge density of the ferromagnetic
order parameter. We show here that for an antiferromagnet, there are two
``fictitious'' ma... | 0108113v1 |
2001-08-15 | Ground State Energy Fluctuations of a System Coupled to a Bath | It is often argued that a small non-degenerate quantum system coupled to a
bath has a fixed energy in its ground state since a fluctuation in energy would
require an energy supply from the bath. We consider a simple model of a
harmonic oscillator (the system) coupled to a linear string and determine the
mean squared en... | 0108243v2 |
2001-08-23 | Critical Behaviour of Non-Equilibrium Phase Transitions to Magnetically Ordered States | We describe non-equilibrium phase transitions in arrays of dynamical systems
with cubic nonlinearity driven by multiplicative Gaussian white noise.
Depending on the sign of the spatial coupling we observe transitions to
ferromagnetic or antiferromagnetic ordered states. We discuss the phase
diagram, the order of the tr... | 0108379v1 |
2001-09-03 | Coulomb drag shot noise in coupled Luttinger liquids | Coulomb drag shot noise has been studied theoretically for 1D interacting
electron systems, which are realized e.g. in single-wall nanotubes. We show
that under adiabatic coupling to external leads, the Coulomb drag shot noise of
two coupled or crossed nanotubes contains surprising effects, in particular a
complete loc... | 0109022v2 |
2001-09-19 | Dynamical mean-field theory for the normal phase of the attractive Hubbard model | We analyze the normal phase of the attractive Hubbard model within dynamical
mean-field-theory. We present results for the pair-density, the
spin-susceptibility, the specific heat, the momentum distribution, and for the
quasiparticle weight. At weak coupling the low-temperature behavior of all
quantities is consistent ... | 0109343v1 |
2001-09-26 | Coupling of thermal and mass diffusion in regular binary thermal lattice-gases | We have constructed a regular binary thermal lattice-gas in which the thermal
diffusion and mass diffusion are coupled and form two nonpropagating diffusive
modes. The power spectrum is shown to be similar in structure as for the one in
real fluids, in which the central peak becomes a combination of coupled entropy
and... | 0109484v1 |
2001-10-25 | Re-examination of orbital ordering in LaMnO$_3$: Electron-electron and electron-lattice interactions | The interactions between $e_g$ orbitals in neighboring sites are investigated
in LaMnO$_3$ by taking into account virtual exchange of electrons and phonons.
The spin and orbital ordering temperatures and the spin wave dispersion
relation are calculated. We find that the orbital ordering is mainly caused by
the electron... | 0110534v1 |
2001-10-28 | Polaron self-trapping in a honeycomb net | Small polaron behavior in a two dimensional honeycomb net is studied by
applying the strong coupling perturbative method to the Holstein molecular
crystal model. We find that small optical polarons can be mobile also if the
electrons are strongly coupled to the lattice. Before the polarons localize and
become very heav... | 0110580v1 |
2001-11-09 | Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment | We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition.The addition of a
parallel ground plane in proximity to the film changes the character of the
transition.Although the screening effects expected from "dirty-boson" theories
are not evident,th... | 0111179v2 |
2001-11-18 | Length scales coupling for nonlinear dynamical problems in magnetism | The dynamics of real magnets is often governed by several interacting
processes taking place simultaneously at different length scales. For dynamical
simulations the relevant length scales should be coupled, and the energy
transfer accurately described. We show that in this case the micromagnetic
theory is not always r... | 0111324v1 |
2001-11-26 | On-line learning and generalisation in coupled perceptrons | We study supervised learning and generalisation in coupled perceptrons
trained on-line using two learning scenarios. In the first scenario the teacher
and the student are independent networks and both are represented by an
Ashkin-Teller perceptron. In the second scenario the student and the teacher
are simple perceptro... | 0111493v1 |
2001-11-26 | Numerical Renormalization Group Study of the Anderson-Holstein Impurity Model | We present numerical renormalization group (NRG) calculations for a
single-impurity Anderson model with a linear coupling to a local phonon mode.
We calculate dynamical response functions, spectral densities, dynamic charge
and spin susceptibilities. Being non-perturbative, the NRG is applicable for
all parameter regim... | 0111496v1 |
2001-12-12 | Quantum Phase Transition in Coupled Spin Ladders | The ground state of an array of coupled, spin-half, antiferromagnetic ladders
is studied using spin-wave theory, exact diagonalization (up to 36 sites) and
quantum Monte Carlo techniques (up to 256 sites). Our results clearly indicate
the occurrence of a zero-temperature phase transition between a N\'eel ordered
and a ... | 0112206v1 |
2002-01-16 | Cooper Pair Box Coupled to a Current-Biased Josephson Junction | We study the dynamics of a quantum superconducting circuit which consists of
a Josephson charge qubit, coupled capacitively to a current biased Josephson
junction. Under certain conditions, the eigenstates of the qubit and the
junction become entangled. We obtain the time evolution of these states in the
limit of weak ... | 0201284v1 |
2002-01-18 | Coherent quantum oscillations in coupled traps with ultracold atoms | The dynamics of two traps with ultracold atoms and connected by Josephson
type coupling, is shown to exhibit a transition from dispersive dynamics to
localized coherent oscillations. This transition is controlled by coupling
strength and energy offset between the traps. The dynamics is also shown to be
exactly that of ... | 0201335v1 |
2002-01-28 | Synchronization in large populations of limit cycle oscillators with long-range interactions | We study the onset of synchronization in lattices of limit cycle oscillators
with long-range coupling by means of numerical simulations. In this regime the
critical coupling strength depends on the system size and interaction range
reflecting the non extensive behavior of the system, but an adequate scaling
removes the... | 0201508v1 |
2002-02-11 | Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction | We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between diffe... | 0202183v1 |
2002-02-26 | Symmetry breaking in the Hubbard model at weak coupling | The phase diagram of the Hubbard model is studied at weak coupling in two and
three spatial dimensions. It is shown that the Neel temperature and the order
parameter in d=3 are smaller than the Hartree-Fock predictions by a factor of
q=0.2599. For d=2 we show that the self-consistent (sc) perturbation series
bears no r... | 0202492v1 |
2002-04-24 | Quantum feedback control of a solid-state qubit | We have studied theoretically the basic operation of a quantum feedback loop
designed to maintain a desired phase of quantum coherent oscillations in a
single solid-state qubit. The degree of oscillations synchronization with
external harmonic signal is calculated as a function of feedback strength,
taking into account... | 0204516v1 |
2002-05-13 | Effect of Subband Landau Level Coupling to the Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet | In a recent experiment (Phys. Rev. Lett. {\bf 87}, 036903 (2001)), Spielman
et al observed a linearly dispersing collective mode in quantum Hall
ferromagnet. While it qualitatively agrees with the Goldstone mode dispersion
at small wave vector, the experimental mode velocity is slower than that
calculated by previous t... | 0205250v2 |
2002-05-15 | Nonperturbative analysis of coupled quantum dots in a phonon bath | Transport through coupled quantum dots in a phonon bath is studied using the
recently developed real-time renormalization-group method. Thereby, the problem
can be treated beyond perturbation theory regarding the complete interaction. A
reliable solution for the stationary tunnel current is obtained for the case of
mod... | 0205308v1 |
2002-05-23 | Bistable Gradient Networks II: Storage Capacity and Behaviour Near Saturation | We examine numerically the storage capacity and the behaviour near saturation
of an attractor neural network consisting of bistable elements with an
adjustable coupling strength, the Bistable Gradient Network (BGN). For strong
coupling, we find evidence of a first-order "memory blackout" phase transition
as in the Hopf... | 0205465v1 |
2002-06-05 | Coherent coupling dynamics in a quantum dot microdisk laser | Luminescence intensity autocorrelation (LIA) is employed to investigate
coupling dynamics between (In,Ga)As QDs and a high-Q (~7000) resonator with
ultrafast time resolution (150 fs), below and above the lasing threshold at T =
5 K. For QDs resonant and non-resonant with the cavity we observe both a
six-fold enhancemen... | 0206065v1 |
2002-06-19 | Magnetic-field dependence of energy levels in ultrasmall metal grains | We present a theory of mesoscopic fluctuations of g tensors and avoided
crossing energies in a small metal grain. The model, based on random matrix
theory, contains both the orbital and spin contributions to the g tensor. The
two contributions can be experimentally separated for weak spin-orbit coupling
while they merg... | 0206377v1 |
2002-06-20 | Spin switching in semiconductor quantum dots through spin-orbit coupling | The spin-orbit coupling influences the total spin of semiconductor quantum
dots. We analyze the theoretical prediction for the combined effects of
spin-orbit coupling, weak vertical magnetic fields and deformation of the dot.
Our results allow the characterization of the quantum dots as spin switches,
controllable with... | 0206387v2 |
2002-06-24 | Pattern Formation in Phase-Separating Gels with Spontaneous Shear | We study pattern formation in gels undergoing simultaneous phase separation
and orientational ordering. A 2D numerical simulation is performed using a
minimal model of nonlinear elasticity with density-anisotropy coupling. For
strong positive coupling, the collapsed phase elongates along the phase
boundary and buckles,... | 0206419v1 |
2002-06-24 | Quantum diffusion of dipole-oriented indirect excitons in coupled quantum wells | A model for diffusion of statistically-degenerate excitons in (coupled)
quantum wells is proposed and analysed. Within a microscopic approach, we
derive a quantum diffusion equation, calculate and estimate the self-diffusion
coefficient for excitons in quantum wells and derive a modified Einstein
relation adapted to st... | 0206459v1 |
2002-06-30 | Interference Effects between Three Coupled Bose-Einstein Condensates | We study the interference effects between three weakly linked trapped
Bose-Einstein condensates (BEC) as a generalization of the two-component
condensates. Three coupled Gross-Pitaevskii equations (GPE) are used to
describe the dynamics of the system. The nonsinusoidal oscillation is found as
a generalization of the Jo... | 0207018v1 |
2002-07-09 | A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field | We present experimental results for the ground state electrochemical
potentials of a few electron semiconductor artificial molecule made by
vertically coupling two quantum dots, in the intermediate coupling regime, in
perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative
analysis based on loca... | 0207242v1 |
2002-07-16 | Low temperature properties of a quantum particle coupled to dissipative environments | We study the dynamics of a quantum particle coupled to dissipative (ohmic)
environments, such as an electron liquid. For some choices of couplings, the
properties of the particle can be described in terms of an effective mass. A
particular case is the three dimensional dirty electron liquid. In other
environments, like... | 0207381v1 |
2002-07-23 | System size coherence resonance | We show the existence of a system size coherence resonance effect for an
ensemble of globally coupled excitable systems. Namely, we demonstrate
numerically that the regularity in the signal emitted by an ensemble of
globally coupled Fitzhugh-Nagumo systems, under excitation by independent noise
sources, is optimal for ... | 0207553v1 |
2002-08-22 | Electronic spin precession in semiconductor quantum dots with spin-orbit coupling | The electronic spin precession in semiconductor dots is strongly affected by
the spin-orbit coupling. We present a theory of the electronic spin resonance
at low magnetic fields that predicts a strong dependence on the dot occupation,
the magnetic field and the spin-orbit coupling strength. Coulomb interaction
effects ... | 0208425v1 |
2002-08-28 | Non-equilibrium Kondo effect in asymmetrically coupled quantum dot | The quantum dot asymmetrically coupled to the external leads has been
analysed theoretically by means of the equation of motion (EOM) technique and
the non-crossing approximation (NCA). The system has been described by the
single impurity Anderson model. To calculate the conductance across the device
the non-equilibriu... | 0208560v1 |
2002-09-20 | Non-universality in Ising models with four spin interaction | We consider two bidimensional classical Ising models, coupled by a weak
interaction bilinear in the energy densities of the two systems; the model
contains, as limiting cases, the Ashkin-Teller and the Eight-vertex models for
certain values of their parameters. We write the energy-energy correlations and
the specific h... | 0209489v1 |
2002-09-25 | Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural transition | Polycrystalline Ni2.18Mn0.82Ga Heusler alloys with a coupled
magnetostructural transition are studied by differential scanning calorimetry,
magnetic and resistivity measurements. Coupling of the magnetic and structural
subsystems results in unusual magnetic features of the alloy. These uncommon
magnetic properties of N... | 0209574v1 |
2002-09-25 | Condensation energy in strongly coupled superconductors | We consider the condensation energy in superconductors where the pairing is
electronic in origin and is mediated by a collective bosonic mode.
We use magnetically-mediated superconductivity as an example, and show that
for large spin-fermion couplings, the physics is qualitatively different from
the BCS theory as the... | 0209600v1 |
2002-09-30 | Phase diagrams of spin ladders with ferromagnetic legs | The low-temperature properties of the spin S=1/2 ladder with anisotropic
ferromagnetic legs are studied using the continuum limit bosonization approach.
The weak-coupling ground state phase diagram of the model is obtained for a
wide range of coupling constants and several unconventional gapless
''spin-liquid'' phases ... | 0209677v1 |
2002-10-28 | Numerical Study of Excited States in the Shastry-Sutherland Model | We investigate excited states of the Shastry-Sutherland model using a kind of
variational method. Starting from various trial states which include one or two
triplet dimers, we numerically pursue the best evaluation of the energy for
each set of quantum numbers. We present the energy difference as a function of
either ... | 0210602v1 |
2002-11-01 | A novel approach to synchronization in coupled excitable systems | We consider networks of coupled stochastic oscillators. When coupled we find
strong collective oscillations, while each unit remains stochastic. In the
limit (N\to \infty) we derive a system of integro-delay equations and show
analytically that the collective oscillations persist in a large region in
parameter. For a r... | 0211011v1 |
2002-11-05 | Phonon dispersion and electron-phonon interaction for YBa_2Cu_3O_7 from first-principles calculations | We present a first principles investigation of the lattice dynamics and
electron-phonon coupling of the high-T_c superconductor YBa_2Cu_3O_7 within the
framework of density functional perturbation theory using a mixed-basis
pseudopotential method. The calculated phonon dispersion curves are in
excellent agreement with ... | 0211084v1 |
2002-11-07 | Comment on ``BCS to Bose-Einstein crossover phase diagram at zero temperature for a d_{x^2-y^2} order parameter superconductor: Dependence on the tight-binding structure'' | The work by Soares et al. [Phys. Rev. B 65, 174506 (2002)] investigates the
BCS-BE crossover for d-wave pairing in the 2-dimensional attractive Hubbard
model. Contrary to their claims, we found that a non-pairing region does not
exist in the density vs coupling phase diagram. The gap parameter at T=0, as
obtained by so... | 0211132v1 |
2002-11-14 | Coupled three-state oscillators | We investigate globally coupled stochastic three-state oscillators, which we
consider as general models of stochastic excitable systems. We compare two
situations:in the first case the transitions between the three states of each
unit 1->2->3->1 are determined by Poissonian waiting time distributions. In the
second cas... | 0211285v1 |
2002-11-15 | Self-Similar Approximations for a Trapped Bose-Einstein Condensate | An approximate solution to the Gross-Pitaevskii equation for Bose-Einstein
condensate in a spherical harmonic trap is suggested, which is valid in the
whole interval of the coupling parameter, correctly interpolating between
weak-coupling and strong-coupling limits. This solution is shown to be more
accurate than the o... | 0211318v1 |
2002-11-25 | Electrical Manipulation of Nanomagnets | We demonstrate a possibility to manipulate the magnetic coupling between two
nanomagnets with a help of ac electric field. In the scheme suggested the
magnetic coupling in question is mediated by a magnetic particle contacting
with both of the nanomagnets through the tunnel barriers. The electric field
providing a succ... | 0211563v1 |
2002-11-27 | Doped coupled frustrated spin-1/2 chains with four-spin exchange | The role of various magnetic inter-chain couplings is investigated by
numerical methods in doped frustrated quantum spin chains. A non-magnetic
dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The
formation of a local magnetic moment is analyzed in term of soliton
confinement. A four-spin coup... | 0211634v3 |
2002-11-30 | Quantum tunneling of two coupled single-molecular magnets | Two single-molecule magnets are coupled antiferromagnetically to form a
supramolecule dimer. We study the coupling effect and tunneling process by
means of the numerical exact diagonalization method, and apply them to the
recently synthesized supramoleculer dimer [Mn4]2 The model parameters are
calculated for the dimer... | 0212002v1 |
2002-12-03 | Thermal stability of coupled ferromagnetic and superparamagnetic particles | We consider a single-domain ferromagnetic particle with uniaxial anisotropy
coupled to a single-domain soft ferromagnetic particle (superparamagnetic
particle). The problem of thermally agitated magnetization reversal in this
case can be reduced to the random magnetization dynamics of the first particle
with an effecti... | 0212041v1 |
2002-12-12 | Endohedral Impurities in Carbon Nanotubes | A generalization of the Anderson model that includes pseudo-Jahn-Teller
impurity coupling is proposed to describe distortions of an endohedral impurity
in a carbon nanotube. Treating the distortion within mean-field theory,
spontaneous axial symmetry breaking is found when the vibronic coupling
strength g exceeds a cri... | 0212269v1 |
2002-12-13 | Quantum oscillations in two coupled charge qubits | Despite an apparent progress in implementing individual solid-state qubits,
there have been no experimental reports so far on multi-bit gates required for
building a real quantum computer. Here we report a new circuit comprising two
coupled charge qubits. Using a pulse technique, we coherently mix quantum
states and ob... | 0212314v1 |
2003-01-09 | Energy dependence of commensurate neutron scattering peak in doped two-leg ladder antiferromagnet Sr_{14-x}Ca_{x}Cu_{24}O_{41} | The dynamical spin response of doped two-leg ladder antiferromagnets is
investigated based on the fermion-spin approach. Our calculations clearly
demonstrate a crossover from the incommensurate antiferromagnetism in the weak
interchain coupling regime to commensurate spin fluctuation in the strong
interchain coupling r... | 0301113v2 |
2003-01-28 | Topological Atom Laser | We demonstrate how a topological atom laser can be realized by output
coupling a trapped vortex state with a Raman scattering process. We find a
linearized analytic solution from which a generalized resonance condition for
Raman output coupling is developed. Using numerical simulations of a two
component Gross-Pitaevsk... | 0301554v1 |
2003-02-12 | Phase transitions towards frequency entrainment in large oscillator lattices | We investigate phase transitions towards frequency entrainment in large,
locally coupled networks of limit cycle oscillators. Specifically, we simulate
two-dimensional lattices of pulse-coupled oscillators with random natural
frequencies, resembling pacemaker cells in the heart. As coupling increases,
the system seems ... | 0302234v1 |
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