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1997-07-23
|
Damping of Growth Oscillations in Molecular Beam Epitaxy: A Renormalization Group Approach
|
The conserved Sine-Gordon Equation with nonconserved shot noise is used to
model homoepitaxial crystal growth. With increasing coverage the renormalized
pinning potential changes from strong to weak. This is interpreted as a
transition from layer-by-layer to rough growth. The associated length and time
scales are identified, and found to agree with recent scaling arguments. A
heuristically postulated nonlinear term $\nabla^2 (\nabla h)^2$ is created
under renormalization.
|
9707247v1
|
1997-09-30
|
AC transport with reservoirs of finite width
|
The linear response conductance coefficients are calculated in the scattering
approach at finite frequency, damping and magnetic field for a microstructure
in which the reservoirs are modeled as quantum wire leads of infinite length
but finite width. Independently of frequency, inelastic scattering causes
subbands with large group velocity to contribute more strongly to the
conductance than channels of comparable transmission but slower propagation. At
finite frequency and magnetic fields, additional correction terms appear, some
of which are sensitive to the phase of the S matrix.
|
9709332v2
|
1997-10-08
|
Spin and orbital excitation spectrum in the Kugel-Khomskii model
|
We discuss spin and orbital ordering in the twofold orbital degenerate
superexchange model in three dimensions relevant to perovskite transition metal
oxides. We focus on the particular point on the classical phase diagram where
orbital degeneracy is lifted by quantum effects exclusively. Dispersion and
damping of the spin and orbital excitations are calculated at this point taking
into account their mutual interaction. Interaction corrections to the
mean-field order parameters are found to be small. We conclude that
quasi-one-dimensional Neel spin order accompanied by the uniform
d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.
|
9710070v1
|
1997-10-21
|
Sound waves and the absence of Galilean invariance in flocks
|
We study a model of flocking for a very large system (N=320,000) numerically.
We find that in the long wavelength, long time limit, the fluctuations of the
velocity and density fields are carried by propagating sound modes, whose
dispersion and damping agree quantitatively with the predictions of our
previous work using a continuum equation. We find that the sound velocity is
anisotropic and characterized by its speed $c$ for propagation perpendicular to
the mean velocity $<\vec{v}>$, $<\vec{v}>$ itself, and a third velocity
$\lambda <\vec{v}>$, arising explicitly from the lack of Galilean invariance in
flocks.
|
9710222v1
|
1997-12-20
|
Collective Excitations in High-Temperature Superconductors
|
Collective, low-energy excitations in quasi-two-dimensional d-wave
superconductors are analyzed. While the long-range Coulomb interaction shifts
the charge-density-wave and phase modes up to the plasma energy, the
spin-density-wave excitation that arises due to a strong local
electron-electron repulsion can propagate as a damped collective mode within
the superconducting energy gap. It is suggested that these excitations are
relevant to high-Tc superconductors, close to the antiferromagnetic phase
boundary, and may explain some of the exotic features of the experimentally
observed spectral-density and neutron-scattering data.
|
9712255v1
|
1998-01-25
|
Excitations of a Bose-Einstein Condensate at Non-Zero Temperature: A Study of Zeroth, First and Second Sound
|
Collective excitations of a dilute Bose gas were probed above and below the
Bose-Einstein condensation temperature. The temperature dependencies of the
frequency and damping rates of condensate oscillations indicate significant
interactions between the condensate and the thermal cloud. Hydrodynamic
oscillations of the thermal cloud were observed, constituting first sound. An
antisymmetric dipolar oscillation of the thermal cloud and the condensate was
studied, representing the bulk flow of a superfluid through the normal fluid.
The excitations were observed in situ using non-destructive imaging techniques.
|
9801262v1
|
1998-02-17
|
Escape from a metastable well under a time-ramped force
|
Thermally activated escape of an over-damped particle from a metastable well
under the action of a time-ramped force is studied. We express the mean first
passage time (MFPT) as the solution to a partial differential equation, which
we solve numerically for a model case. We discuss two approximations of the
MFPT, one of which works remarkably well over a wide range of loading rates,
while the second is easy to calculate and can provide a valuable first
estimate.
|
9802182v1
|
1998-03-02
|
On temperature versus doping phase diagram of high critiical temperature superconductors
|
The attempt to describe the bell-shape dependence of the critical temperature
of high-$T_{c}$ superconductors on charge carriers density is made. Its linear
increase in the region of small densities (underdoped regime) is proposed to
explain by the role of the order parameter phase 2D fluctuations which become
less at this density growth. The critical temperature suppression in the region
of large carrier densities (overdoped regime) is connected with the appearance
(because of doping) of the essential damping of long-wave bosons which in the
frame of the model proposed define the mechanism of indirect inter-fermion
attraction.
|
9803011v1
|
1998-03-02
|
Evolution of Hole and Spin Dynamics in High Temperature Superconductors within the Small Hole Density Limit of the t-J Model
|
The evolution of hole and spin dynamics in high temperature superconductors
is studied within the self-consistent noncrossing approximation of the t-J
model in the small hole density limit. As the doping concentration is
increased, long-range electron correlations disappear rapidly and the
quasiparticle energy band becomes considerably narrow. At a small hole density
long-range antiferromagnetic order is destroyed leading to the inadequacy of
spin wave basis approximation near small wave vectors. Spin excitations near
the antiferromagnetic zone boundary are strongly renormalized and damped but
they are still well described within spin wave basis approximation.
|
9803016v1
|
1998-04-14
|
The dynamics of component separation in a binary mixture of Bose-Einstein condensates
|
We present studies of the time-evolution of a two-component system of
Bose-Einstein condensates (BEC) in the |F=1, mf=-1> and |2,1> spin states of
Rb-87. The two condensates are created with a well-defined relative phase and
complete spatial overlap. In subsequent evolution they undergo complex relative
motions which tend to preserve the total density profile. the motions quickly
damp out, leaving the condensates in a steady state with a nonnegligible (and
adjustable) overlap region.
|
9804138v1
|
1998-04-17
|
Relaxation Processes in Clouds of Trapped Bosons above the Bose-Einstein Condensation Temperature
|
We present a unified account of damping of low-lying collective modes and of
relaxation of temperature anisotropies in a trapped Bose gas in the
collisionless regime. By means of variational techniques, we show that the
relaxation times for the two situations are closely related to the simplest
variational estimate of the viscous relaxation time. We derive rather precise
theoretical expressions for the characteristic relaxation times, and compare
our results with experiment.
|
9804193v1
|
1998-05-01
|
Hot electron transport in Ballistic Electron Emission Spectroscopy: band structure effects and k-space currents
|
Using a Green's function approach, we investigate band structure effects in
the BEEM current distribution in reciprocal space. In the elastic limit, this
formalism provides a 'parameter free' solution to the BEEM problem. At low
temperatures, and for thin metallic layers, the elastic approximation is enough
to explain the experimental I(V) curves at low voltages. At higher voltages
inelastic effects are approximately taken into account by introducing an
effective RPA-electron lifetime, much in similarity with LEED theory. For thick
films, however, additional damping mechanisms are required to obtain agreement
with experiment.
|
9805007v1
|
1998-05-25
|
Measurements of Relative Phase in Binary Mixtures of Bose-Einstein Condensates
|
We have measured the relative phase of two Bose-Einstein condensates (BEC)
using a time-domain separated-oscillatory-field condensate interferometer. A
single two-photon coupling pulse prepares the double condensate system with a
well-defined relative phase; at a later time, a second pulse reads out the
phase difference accumulated between the two condensates. We find that the
accumulated phase difference reproduces from realization to realization of the
experiment, even after the individual components have spatially separated and
their relative center-of-mass motion has damped.
|
9805327v1
|
1998-08-04
|
Quantum energy flow, dissipation and decoherence in mesoscopic dielectric structures
|
We first present a summary of recent results concerning the phononic energy
transport properties of mesoscopic, suspended dielectric wires. We then discuss
some related open problems concerning the fundamental lower limits on the
vibrational damping rates of submicron-sized cantilever structures and also the
possibility to create and detect quantum superpositions of spatially separated
states for such structures.
|
9808032v1
|
1998-08-17
|
Exact General Solutions to Extraordinary N-body Problems
|
We solve the N-body problems in which the total potential energy is any
function of the mass-weighted root-mean-square radius of the system of N point
masses. The fundamental breathing mode of such systems vibrates non-linearly
for ever. If the potential is supplemented by any function that scales as the
inverse square of the radius there is still no damping of the fundamental
breathing mode. For such systems a remarkable new statistical equilibrium is
found for the other coordinates and momenta, which persists even as the radius
changes continually.
|
9808173v1
|
1998-08-19
|
Collective Modes in High-Temperature Superconductors
|
The role of collective modes in various experiments on the cuprates is
investigated. We calculate the neutron scattering, photoemission (ARPES), and
Raman scattering intensities below $T_c$ within the fluctuation-exchange (FLEX)
approximation for the two-dimensional Hubbard model. It is shown that the large
peak in the dynamical spin susceptibility arises from a weakly damped
spin-density-wave collective mode. This gives rise to a dip between the sharp
low energy peak and the higher binding energy hump in the ARPES spectrum.
Furthermore, we show that the collective mode of the amplitude fluctuation of
the d-wave gap yields a broad peak above the pair-breaking threshold in the
$B_{1g}$ Raman spectrum.
|
9808210v1
|
1998-09-03
|
Dynamics of two interacting Bose-Einstein condensates
|
We analize the dynamics of two trapped interacting Bose-Einstein condensates
and indentify two regimes for the evolution: the regime of slow periodic
oscillations and the regime of strong non-linear mixing leading to the damping
of the relative motion of the condensates. We compare our predictions with an
experiment recently performed at JILA.
|
9809061v2
|
1998-10-05
|
Quantum critical point with competing propagating and diffusive spin excitations
|
Feedback effects due to spin fluctuation induced precursors in the fermionic
quasiparticle spectrum are taken into account in the description of a quantum
critical point of itinerant spin systems. A correlation length dependent spin
damping occurs, leading to a dynamical scaling with z\approx 1 which
non-trivially competes with the conventional spin wave behavior. We obtain,
within a one loop renormalization group approach, a quantitative explanation
for the scaling behavior seen in underdoped cuprate superconductors.
|
9810041v1
|
1998-10-30
|
The Markov approximation for the atomic output coupler
|
The regions of validity of the Markov approximation for the coupling of atoms
out of an atomic trap are determined. We consider radio-frequency output
coupling in the presence of gravity and collisional repulsion, and Raman output
coupling. The Markov approximation is crucial in most theoretical descriptions
of an atom laser that assume a continuous process of output coupling from a
trapped Bose-Einstein condensate. In this regime many techniques proved to be
useful for modeling the optical laser, such as master equations, can be used to
describe the dynamics of the damping of the condensate mode undergoing output
coupling.
|
9810413v1
|
1998-11-18
|
A Stochastic Liouvillian Algorithm to Simulate Dissipative Quantum Dynamics With Arbitrary Precision
|
An exact and efficient new method to simulate dynamics in dissipative quantum
systems is presented. A stochastic Liouville equation, deduced from Feynman and
Vernon's path-integral expression of the reduced density matrix, is used to
describe the exact dynamics at any dissipative strength and for arbitrarily low
temperatures. The utility of the method is demonstrated by applications to a
damped harmonic oscillator and a double-well system immersed in an Ohmic bath
at low temperatures.
|
9811277v1
|
1998-12-01
|
Polarons in Wurtzite Nitride Semiconductors
|
Polaron binding energy and effective mass are calculated for semiconductors
with wurtzite crystalline structure from the first order electron-phonon
corrections to the self-energy. A recently introduced Frohlich-like
electron-phonon interaction Hamiltonian which accounts for the LO and TO
polarizations mixing due to the anisotropy is used in the calculation. The
polaronic damping rates are evaluated for finite temperature. Numerical results
are reported for GaN. It is shown that the electron-phonon coupling is strong
enough to justify the necessity of the inclusion of second-order corrections.
|
9812021v1
|
1998-12-24
|
Straight cracks in dynamic brittle fracture
|
We study the dynamics of cracks in brittle materials when the velocity of the
crack is comparable to the sound velocity by means of lattice simulations.
Inertial and damped dynamics are analyzed. It is shown that dissipation
strongly influences the shape of the crack. While inertial cracks are highly
unstable, dissipation can stabilize straight cracks. Our results can help to
explain recent experiments on PMMA.
|
9812391v1
|
1999-02-08
|
On the Reconstruction of Random Media using Monte Carlo Methods
|
A simulated annealing algorithm is applied to the reconstruction of
two-dimensional porous media with prescribed correlation functions. The
experimental correlation function of an isotropic sample of Fontainebleau
sandstone and a synthetic correlation function with damped oscillations are
used in the reconstructions. To reduce the numerical effort we follow a
proposal suggesting to evaluate the correlation functions only along certain
directions. The results show, that this simplification yields significantly
different micro-structures as compared to a full evaluation of the correlation
function. In particular we find that the simplified reconstruction method
introduces an artificial anisotropy that is originally not present.
|
9902096v1
|
1999-03-18
|
On the electron-energy loss spectra and plasmon resonance in cuprates
|
The consequences of the non-Drude charge response in the normal state of
cuprates and the effect of the layered structure on electron-energy loss
spectra are investigated, both for experiments in the transmission and the
reflection mode. It is shown that in the intermediate doping regime the plasmon
resonance has to be nearly critically damped as a result of the anomalous
frequency dependence of the relaxation rate. This also implies an unusual
low-energy dependence of the loss function. Both facts are consistent with
experiments in cuprates. Our study based on the t-J model shows good agreement
with measured plasmon frequencies.
|
9903287v1
|
1999-04-26
|
Magnon Damping by magnon-phonon coupling in Manganese Perovskites
|
Inelastic neutron scattering was used to systematically investigate the
spin-wave excitations (magnons) in ferromagnetic manganese perovskites. In
spite of the large differences in the Curie temperatures ($T_C$s) of different
manganites, their low-temperature spin waves were found to have very similar
dispersions with the zone boundary magnon softening. From the wavevector
dependence of the magnon lifetime effects and its correlation with the
dispersions of the optical phonon modes, we argue that a strong magneto-elastic
coupling is responsible for the observed low temperature anomalous spin
dynamical behavior of the manganites.
|
9904372v1
|
1999-04-28
|
Collective oscillations of a classical gas confined in harmonic traps
|
Starting from the Boltzmann equation we calculate the frequency and the
damping of the monopole and quadrupole oscillations of a classical gas confined
in an harmonic potential. The collisional term is treated in the relaxation
time approximation and a gaussian ansatz is used for its evaluation. Our
approach provides an explicit description of the transition between the
hydrodynamic and collisionless regimes in both spherical and deformed traps.
The predictions are compared with the results of a numerical simulation.
|
9904409v1
|
1999-05-11
|
Magnon Broadening Effect by Magnon-Phonon Interaction in Colossal Magnetoresistance Manganites
|
In order to study the magnetic excitation behaviors in colossal
magnetoresistance manganites, a magnon-phonon interacting system is
investigated. Sudden broadening of magnon linewidth is obtained when a magnon
branch crosses over an optical phonon branch. Onset of the broadening is
approximately determined by the magnon density of states. Anomalous magnon
damping at the brillouine zone boundary observed in low Curie temperature
manganites is explained.
|
9905133v2
|
1999-06-03
|
Effects of noise and nonlocal interactions in nonlinear dynamics of molecular systems
|
We show that the NLS systems with multiplicative noise, nonlinear damping and
nonlocal dispersion exhibit a variety of interesting effects which may be
useful for modelling the dynamical behavior of one- and two-dimensional
molecular systems.
|
9906050v1
|
1999-06-20
|
Tunneling-Assisted Acoustic Plasmon-Quasiparticle Excitation Resonances in Coupled Q1D Electron Gases
|
We show that a weak non-resonant tunneling between two quantum wires leads to
splitting of the acoustic plasmon mode at finite wavevector. Two gaps open up
in the dipersion of the acoustic plasmon mode when its frequency is close to
the frequencies of the quasiparticle excitations. In contrast to the Laudau
damping of the collective excitations, these gaps are attributed to tunneling
assisted acoustic plasmon-quasiparticle excitation resonances. We predict that
such a resonance can be observed in inelastic light scattering spectrum.
|
9906306v1
|
1999-07-06
|
New type of antiferromagnetic polaron and bipolaron in HTc - superconductors
|
The possibility of formation of a new type of polaron based on the quantum
aniferromagnet (AF) model is reported. We take into account exchange
interactions between localized d-d spins of the AF, as well as the p-d
interaction of the AF with p-carriers.
The energy minimum is found when maximum charge density occurs on every
second spin. The formation of such ``comb''-like polarons results from the
damping of quantum fluctuations and the appearance of Van Vleck-like staggered
magnetization. Such polarons tend to form pairs coupled by an AF ``glue''.
|
9907081v1
|
1999-08-01
|
Comment on "quantum theory for mesosocopic electric circuits". Cond-mat/9907171 and cond-mat/9606206
|
In references cond-mat/9907171 and cond-mat/9606206 (Phys.Rev.B.53, 4927
(1996)) by You-Quan Li and Bin Chen, was considered a mesoscopic LC circuit
with charge discreteness. So, it was proposed a finite difference Schroedinger
equation for the charge time behavior. In this comment, we generalize the
corresponding mesoscopic Hamiltonian in order to taken into account the
dissipative effects (resistance R). Namely, a quantum term RI, proportional to
the current, is added to the mesoscopic LC circuit equation. This is
carried-out in analogy with the theory of Caldirola-Kanai for quantum one
particle damping.
|
9908012v1
|
1999-09-03
|
Wave Function Mismatches and Coulomb Drag
|
In this paper, I study the topological excitations in a pairing state in
double layer systems at Landau level filling factor $\nu=1/2$ in the presence
of disorders. Due to mismatches between single particle wave functions of
composite Fermions in different layers, the sensitivity of the Chern number of
the pairing state, with respect to changes of impurities, is infinity.
Consequently, Goldstone mode in this pairing state is strongly damped at low
temperature. It is argued that this leads to a unique temperature dependence of
the drag resistance at low temperature.
|
9909051v2
|
1999-10-06
|
Collisional relaxation in diffuse clouds of trapped bosons
|
The damping of collective modes and the relaxation of temperature
anisotropies in a trapped Bose gas is determined at temperatures above the
Bose-Einstein condensation temperature in the collisionless regime. We
demonstrate for both cases how the effects of collisions may be treated
perturbatively and calculate relaxation rates based on a variational principle.
Our results are compared with experiment and with previous theoretical
calculations.
|
9910081v1
|
1999-10-22
|
Driven Tunneling Dynamics: Bloch-Redfield Theory versus Path Integral Approach
|
In the regime of weak bath coupling and low temperature we demonstrate
numerically for the spin-boson dynamics the equivalence between two widely used
but seemingly different roads of approximation, namely the path integral
approach and the Bloch-Redfield theory. The excellent agreement between these
two methods is corroborated by a novel efficient analytical high-frequency
approach: it well approximates the decay of quantum coherence via a series of
damped coherent oscillations. Moreover, a suitably tuned control field can
selectively enhance or suppress quantum coherence.
|
9910359v2
|
1999-10-27
|
A Novel Longitudinal Mode in the Coupled Quantum Chain Compound KCuF3
|
Inelastic neutron scattering measurements are reported that show a new
longitudinal mode in the antiferromagnetically ordered phase of the spin-1/2
quasi-one-dimensional antiferromagnet KCuF3. This mode signals the cross-over
from one-dimensional to three-dimensional behavior and indicates a reduction in
the ordered spin moment of a spin-1/2 antiferromagnet. The measurements are
compared with recent quantum field theory results and are found to be in
excellent agreement. A feature of the data not predicted by theory is a damping
of the mode by decay processes to the transverse spin-wave branches.
|
9910459v1
|
1999-11-12
|
Observation of the scissors mode and superfluidity of a trapped Bose-Einstein condensed gas
|
We report the observation of the scissors mode of a Bose-Einstein condensed
gas of 87^Rb atoms in a magnetic trap, which gives direct evidence of
superfluidity in this system. The scissors mode of oscillation is excited by a
sudden rotation of the anisotropic trapping potential. For a gas above T_c
(normal fluid) we detect the occurrence of oscillations at two frequencies,
with the lower frequency corresponding to the rigid body value of the moment of
inertia. Well below T_c the condensate oscillates at a single frequency,
without damping, as expected for a superfluid.
|
9911195v1
|
1999-11-19
|
Transport in a One-Dimensional Superfluid: Quantum Nucleation of Phase Slips
|
We present an analytical derivation for the quantum decay rate of the
superflow through a weak link in a one-dimensional Bose-Einstein-condensate.
The effective action for the phase difference across the link reduces to that
of a massive particle with damping subject to a periodic potential. We find an
algebraic flow-pressure relation, characteristic for quantum nucleation of
phase slips in the link and show how short-wave length fluctuations
renormalizing the interaction between the Bosons remove the quantum phase
transition expected in this class of systems.
|
9911301v1
|
1999-11-26
|
Kadanoff-Baym Equations with Initial Correlations
|
The Kadanoff-Baym equations (KBE) are usually derived under the assumption of
the weakening of initial correlations (Bogolyubov's condition) and, therefore,
fail to correctly describe the short time behavior. We demonstrate that this
assumption is not necessary. Using functional derivatives techniques, we
present a straightforward generalization of the KBE which allows to include
arbitrary initial correlations and which is more general than previous
derivations. As a result, an additional collision integral is obtained which is
being damped out after a few collisions. Our results are complemented with
numerical investigations showing the effect of initial correlations.
|
9911429v1
|
1999-12-08
|
Thermodynamical fluctuations and photo-thermal shot noise in gravitational wave antennae
|
Thermodynamical fluctuations of temperature in mirrors of gravitational wave
antennae are transformed through thermal expansion coefficient into additional
noise. This source of noise, which may also be interpreted as fluctuations due
to thermoelastic damping, may not be neglected and leads to the necessity to
reexamine the choice of materials for the mirrors. Additional source of noise
are fluctuations of the mirrors' surfaces caused by optical power absorbed in
dielectrical reflective layers.
|
9912139v1
|
2000-01-25
|
Motion of dark solitons in trapped Bose-Einstein condensates
|
We use a multiple time scale boundary layer theory to derive the equation of
motion for a dark (or `grey') soliton propagating through an effectively
one-dimensional cloud of Bose-Einstein condensate, assuming only that the
background density and velocity vary slowly on the soliton scale. We show that
solitons can exhibit viscous or radiative acceleration (anti-damping), which we
estimate as slow but observable on experimental time scales.
|
0001360v1
|
2000-02-01
|
Fractional Kramers Equation
|
We introduce a fractional Kramers equation for a particle interacting with a
thermal heat bath and external non-linear force field. For the force free case
the velocity damping follows the Mittag-Leffler relaxation and the diffusion is
enhanced. The equation obeys the generalized Einstein relation, and its
stationary solution is the Boltzmann distribution. Our results are compared to
previous results on enhanced L\'evy type of diffusion derived from stochastic
collision models.
|
0002020v1
|
2000-02-20
|
Impurity spin dynamics in 2D antiferromagnets and superconductors
|
We discuss the universal theory of localized impurities in the paramagnetic
state of 2D antiferromagnets where the spin gap is assumed to be significantly
smaller than a typical exchange energy. We study the impurity spin
susceptibility near the host quantum transition from a gapped paramagnet to a
Neel state, and we compute the impurity-induced damping of the spin-1 mode of
the gapped antiferromagnet. Under suitable conditions our results apply also to
d-wave superconductors.
|
0002316v1
|
2000-03-01
|
Short, Medium and Long Range Spatial Correlations in Simple Glasses
|
Local stresses and pressures always exist in glasses.
In this letter we consider their effects on the structure and structural
correlations in simple glasses. We find that extreme values of local pressures
are related to well defined local structures. The correlations related to these
extreme stresses extend to full system size and decay as a power law with the
distance.
This result is especially striking, since at large scales, the total density
fluctuation exhibits exponentially damped decay similar to the decay in simple
liquids. Thus at medium and large distances, the atoms with extreme values of
local pressures exhibit higher degree of correlation than the rest of the
system. These results were found for glasses with very different short range
structure, indicating their general nature.
|
0003006v1
|
2000-03-03
|
Heat Conduction and Charge Ordering in Perovskite Manganites, Nickelates and Cuprates
|
We discuss heat transport in hole-doped manganites, nickelates and cuprates
for which real-space charge ordering has been observed. We survey the thermal
transport response to charge order in the various materials and the associated
structural modifications, particularly distortions of the metal-oxygen
polyhedra associated with localized charge, that may be a principal source of
phonon damping.
|
0003047v1
|
2000-04-08
|
Asymptotic states in long Josephson junctions in an external magnetic field
|
Asymptotic states in long Josephson junctions are investigated in an external
magnetic field. We show that a choice one of the solution of the stationary
Ferrell-Prange equation can carry be out with use of an asymptotic solution of
the sine-Gordon equation and that an evolution to that stable solution occurs
by passing through metastable states, which is determined with a form of
quickly damped initial perturbation. The boundary sine-Gordon and
Ferrell-Prange problems were carried out with a numerical simulation. An
approximated expression for the vortex and antivortex states is obtained in the
case of large values of an external magnetic field.
|
0004120v1
|
2000-04-20
|
Peculiarities of anharmonic lattice dynamics and thermodynamics of alkaline-earth metals
|
The calculations are performed for a broad range of the properties of Ca and
Sr in the fcc and bcc phases. A detailed information on the magnitude and
character of temperature dependence of anharmonic effects in the lattice
dynamics over the entire Brillouin zone (frequency shifts and phonon damping,
Gruneisen parameters) is given. A detailed comparison of the computational
results for the heat capacity and thermal expansion with the experimental data
is carried out; the theoretical results are in good agreement with the
experiment.
|
0004353v1
|
2000-06-20
|
Final Generalization of the Three Coupled Oscillator Model in the Crystal Optical Activity
|
In this paper we generalize the quantum mechanical model of three coupled
oscillators because of its usage in the crystal optical activity. Using this
model we can include the influence of all essential couplings between single
oscillators which represent the molecules or atoms of optically active crystals
belonging for example to the space groups of symmetry D(3,4) or D(3,6). The
single oscillators are damped and therefore we can include both parts of the
optical activity - optical rotatory dispersion and circular dichroism - into
computations. We present more universal formulas for description of the above
mentioned parts.
|
0006299v1
|
2000-07-03
|
Dynamics of Fluctuating Bose-Einstein Condensates
|
We present a generalized Gross-Pitaevskii equation that describes also the
dissipative dynamics of a trapped partially Bose condensed gas. It takes the
form of a complex nonlinear Schr\"odinger equation with noise. We consider an
approximation to this Langevin field equation that preserves the correct
equilibrium for both the condensed and the noncondensed parts of the gas. We
then use this formalism to describe the reversible formation of a
one-dimensional Bose condensate, and compare with recent experiments. In
addition, we determine the frequencies and the damping of collective modes in
this case.
|
0007026v1
|
2000-08-14
|
Manifestation of superfluidity in an evolving Bose-condensed gas
|
We study the generation of excitations due to an ''impurity''(static
perturbation) placed into an oscillating Bose-condensed gas in the
time-dependent trapping field. It is shown that there are two regions for the
position of the local perturbation. In the first region the condensate flows
around the ''impurity'' without generation of excitations demonstrating
superfluid properties. In the second region the creation of excitations occurs,
at least within a limited time interval, revealing destruction of
superfluidity. The phenomenon can be studied by measuring the damping of
condensate oscillations at different positions of the ''impurity''.
|
0008207v1
|
2000-10-04
|
Measurement of the energy dependence of phase relaxation by single electron tunneling
|
Single electron tunneling through a single impurity level is used to probe
the fluctuations of the local density of states in the emitter. The energy
dependence of quasi-particle relaxation in the emitter can be extracted from
the damping of the fluctuations of the local density of states (LDOS). At
larger magnetic fields Zeeman splitting is observed.
|
0010070v1
|
2000-10-08
|
Role of entropy barriers for diffusion in the periodic potential
|
Diffusion of a particle in the N-dimensional external potential which is
periodic in one dimension and unbounded in the other N-1 dimensions is
investigated. We find an analytical expression for the overdamped diffusion and
study numerically the cases of moderate and low damping. We show that in the
underdamped limit, the multi-dimensional effects lead to reduction (comparing
with the one-dimensional motion) of jump lengths between subsequent trapping of
the atom in bottoms of the external periodic potential. As application we
consider the diffusion of a dimer adsorbed on the crystal surface.
|
0010125v1
|
2000-10-12
|
Friction in a solid lubricant film
|
Molecular dynamics study of a thin (one to five layers) lubricant film
between two substrates in moving contact are performed using Langevin equations
with an external damping coefficient depending on distance and velocity of
atoms relative the substrates, motivated by microscopic configurations. They
show that the minimal friction coefficient is obtained for the solid-sliding
regime. A detailed analysis of the results, the comparison with other
microscopic modeling approaches of friction, and the evaluation of quantities
that can be compared to experiments, such as the velocity of the transition
from stick-slip to smooth sliding, are used to discuss the relevance of the
microscopic simulations of friction.
|
0010185v1
|
2001-01-15
|
A classical field method for time dependent Bose condensed gases
|
We propose a method to study the time evolution of Bose condensed gases
perturbed from an initial thermal equilibrium, based on the Wigner
representation of the $N$-body density operator. We show how to generate a
collection of random classical fields sampling the initial Wigner distribution
in the number conserving Bogoliubov approximation. The fields are then evolved
with the time dependent Gross-Pitaevskii equation. We illustrate the method
with the damping of a collective excitation of a one-dimensional Bose gas.
|
0101210v2
|
2001-01-19
|
Ghost excitonic insulator transition in layered graphite
|
Some unusual properties of layered graphite, including a linear energy
dependence of the quasiparticle damping and weak ferromagnetism at low doping,
are explained as a result of the proximity of a single graphene sheet to the
excitonic insulator phase which can be further stabilized in a doped system of
many layers stacked in the staggered ($ABAB...$) configuration.
|
0101306v4
|
2001-01-25
|
Comment on "Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets: Sr2CuO2Cl2 and Sr2Cu3O4Cl2"
|
We compare the neutron measurements of Kim et al. (cond-mat/0012239) on
two-dimensional, S=1/2 antiferromagnets with the continuum quasiclassical
theory of S. Sachdev and O.A. Starykh (cond-mat/9904354). The damping of the
lowest energy spin excitations is characterized by a dimensionless number whose
temperature dependence was predicted to be determined entirely by that of the
uniform spin susceptibility. Theory and experiment are consistent with each
other.
|
0101394v1
|
2001-01-29
|
Enhancement of mobility by periodically modulating the slanting slope of a washboard potential
|
Average mobility of very feebly damped particles in tilted periodic
potentials is considered. Under the combined action of thermal fluctuations and
small temporal modulation of the tilt of the potential the particles, in the
small tilt range, become more mobile than without modulation. The enhancement
of mobility depends (nonmonotonically) on the frequency of modulation. For
small modulations the enhancement shows a peak as a function of frequency. This
has an obvious implication on the measured voltage across a Josephson junction
driven by a small amplitude alternating current of suitable frequency.
|
0101425v1
|
2001-02-26
|
Relaxation time of weakly interacting superparamagnets
|
The relaxation time of weakly interacting classical spins is calculated by
introducing the averages of the local dipolar field, obtained by thermodynamic
perturbation theory, in a rigorous expression for the single-spin
thermoactivation rate in a weak but arbitrarily oriented field. At low
temperatures the non-trivial dependence of the superparamagnetic blocking on
the damping coefficient, numerically found by Berkov and Gorn, is reproduced by
our model and interpreted in terms of the deviations from uniaxial anisotropy
associated to the transversal component of the dipolar field acting on each
spin.
|
0102472v1
|
2001-03-02
|
Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity
|
We have measured the magnetic penetration depth of the recently discovered
binary superconductor MgB_2 using muon spin rotation and low field
$ac$-susceptibility. From the damping of the muon precession signal we find the
penetration depth at zero temperature is about 85nm. The low temperature
penetration depth shows a quadratic temperature dependence, indicating the
presence of nodes in the superconducting energy gap.
|
0103060v1
|
2001-05-09
|
An echo of an exciting light pulse in quantum wells
|
The non-sinusoidal character oscillations appear in the transmitted,
reflected and absorbed light fluxes when light pulses irradiate a semiconductor
quantum well (QW), containing a large number of the equidistant energy levels
of electronic excitations. A damping echo of the exciting pulse appears through
the time intervals $2\pi\hbar/\Delta E$ in the case of the very short light
pulses $\gamma_l^{-1}\ll\hbar/\Delta E$.
|
0105198v1
|
2001-05-18
|
Controlled Generation of Dark Solitons with Phase Imprinting
|
The generation of dark solitons in Bose-Einstein condensates with phase
imprinting is studied by mapping it into the classic problem of a damped driven
pendulum. We provide simple but powerful schemes of designing the phase imprint
for various desired outcomes. We derive a formula for the number of dark
solitons generated by a given phase step, and also obtain results which explain
experimental observations.
|
0105377v1
|
2001-05-22
|
Transition from Collisionless to Hydrodynamic Behaviour in an Ultracold Atomic Gas
|
Relative motion in a two-component, trapped atomic gas provides a sensitive
probe of interactions. By studying the lowest frequency excitations of a two
spin-state gas confined in a magnetic trap, we have explored the transition
from the collisionless to the hydrodynamic regime. As a function of collision
rate, we observe frequency shifts as large as 6% as well as a dramatic,
non-monotonic dependence of the damping rate. The measurements agree
qualitatively with expectations for behavior in the collisionless and
hydrodynamic limits and are quantitatively compared to a classical kinetic
model.
|
0105441v1
|
2001-05-23
|
Finite-temperature simulations of the scissors mode in Bose-Einstein condensed gases
|
The dynamics of a trapped Bose-condensed gas at finite temperatures is
described by a generalized Gross-Pitaevskii equation for the condensate order
parameter and a semi-classical kinetic equation for the thermal cloud, solved
using $N$-body simulations. The two components are coupled by mean fields as
well as collisional processes that transfer atoms between the two. We use this
scheme to investigate scissors modes in anisotropic traps as a function of
temperature. Frequency shifts and damping rates of the condensate mode are
extracted, and are found to be in good agreement with recent experiments.
|
0105465v1
|
2001-06-25
|
Collective Excitations of Dilute Bose-Fermi Superfluid Mixtures
|
Using the effective action formalism, we investigate collective excitations
of a dilute mixture of a Bose gas and a two component Fermi gas when both
bosons and fermions have undergone superfluid transitions. We show that there
is a repulsion between Bogoliubov and Anderson modes, which has important
implications including disappearance of boson superfluidity. We derive an
analytic expression for the long-wavelength dispersion relation of the mixture
at zero temperature and give a condition for the instability. We also
numerically calculate the damping rate due to boson-fermion interaction at
finite temperatures and show that the two modes are stable at sufficiently low
temperatures.
|
0106503v1
|
2001-07-10
|
The formation of vortex loops (strings) in continuous phase transitions
|
The formation of vortex loops (global cosmic strings) in an O(2) linear sigma
model in three spatial dimensions is analyzed numerically. For over-damped
Langevin dynamics we find that defect production is suppressed by an
interaction between correlated domains that reduces the effective spatial
variation of the phase of the order field. The degree of suppression is
sensitive to the quench rate. A detailed description of the numerical methods
used to analyze the model is also reported.
|
0107188v2
|
2001-07-20
|
Theory of sound propagation in superfluid-filled porous media
|
The theory of sound propagation in macroscopically isotropic and homogeneous
porous media saturated with superfluid ^4He(so-called He II) has been developed
neglecting all damping processes. The case when the normal fluid component is
locked inside a porous medium by viscous forces is investigated in detail. It
is shown that in this case one shear wave and two longitudinal, fast and slow,
waves exist. Fast wave as well as slow wave is accompanied with temperature
oscillations. The velocities of these waves are obtained.
|
0107438v3
|
2001-08-11
|
Spin dynamics from time-dependent spin density-functional theory
|
We derive the spin-wave dynamics of a magnetic material from the
time-dependent spin density functional theory in the linear response regime.
The equation of motion for the magnetization includes, besides the static spin
stiffness, a "Berry curvature" correction and a damping term. A gradient
expansion scheme based on the homogeneous spin-polarized electron gas is
proposed for the latter two quantities, and the first few coefficients of the
expansion are calculated to second order in the Coulomb interaction.
|
0108193v1
|
2001-09-20
|
Aging effects in the quantum dynamics of a dissipative free particle: non-ohmic case
|
We report new results related to the two-time dynamics of the coordinate of a
quantum free particle, damped through its interaction with a fractal thermal
bath (non-ohmic coupling $\sim\omega^\delta$ with $0<\delta<1$ or
$1<\delta<2)$. When the particle is localized, its position does not age. When
it undergoes anomalous diffusion, only its displacement may be defined. It is
shown to be an aging variable. The finite temperature aging regime is
self-similar. It is described by a scaling function of the ratio ${t_w/\tau}$
of the waiting time to the observation time, as characterized by an exponent
directly linked to $\delta$.
|
0109368v1
|
2001-09-26
|
Slow relaxation, confinement, and solitons
|
Millisecond crystal relaxation has been used to explain anomalous decay in
doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons.
Our model exhibits confinement of mechanical energy released by excitation.
Extending the model to long times is justified by its relation to solitons,
excitations previously proposed to occur in alkali halides. Soliton damping and
observation are also discussed.
|
0109483v1
|
2001-10-09
|
Quantum decay rates for driven barrier potentials in the strong friction limit
|
Quantum decay rates for barrier potentials driven by external stochastic and
periodic forces in the strong damping regime are studied. Based on the recently
derived quantum Smoluchowski equation [Phys. Rev. Lett. {\bf 87}, 086802
(2001)] explicit analytical and numerical results are presented for the case of
the resonant activation phenomenon in a bistable potential and the escape from
a metastablwell with oscillating barrier, respectively. The significant impact
of quantum fluctuations is revealed.
|
0110169v1
|
2001-10-10
|
Ferromagnetism and disorder: A dynamical mean-field study
|
We investigate ferromagnetism in the periodic Anderson model with diagonal
disorder. Using dynamical mean-field theory in combination with the modified
perturbation theory, the disorder can be included in the calculation
consistently, which turns out to be equivalent to the CPA method. Disorder
generally reduces the Curie temperature and can for certain configurations
completely suppress ferromagnetic order. This can be ascribed to the enhanced
quasiparticle damping and the special structure of the density of states.
|
0110209v1
|
2001-10-29
|
Long-Range Coherence in a Mesoscopic Metal near a Superconducting Interface
|
We identify the different contributions to quantum interference in a
mesoscopic metallic loop in contact with two superconducting electrodes. At low
temperature, a flux-modulated Josephson coupling is observed with strong
damping over the thermal length L_{T}. At higher temperature, the
magnetoresistance exhibits large h/2e-periodic oscillations with 1/T power law
decay. This flux-sensitive contribution arises from coherence of low-energy
quasiparticles states over the phase-breaking length L_{\phi}. Mesoscopic
fluctuations contribute as a small h/e oscillation, resolved only in the purely
normal state.
|
0110584v1
|
2001-11-05
|
Dynamical Behaviour of Fine Granular Glass/Bronze Mixtures under Vertical Vibration
|
We report the behaviour of mixtures of fine bronze and glass spheres under
sinusoidal vertical vibration. Depending upon the ratio of their diameters and
the amplitude and frequency of the vibration, we observe the formation of sharp
separation boundaries between glass-rich and bronze-rich phases, the absence of
gross convection which would mix these phases, and a number of oscillatory and
non-periodic behaviours. These phenomena are related to the differential air
damping of the glass and bronze grains, disappearing completely in the absence
of air.
|
0111064v1
|
2001-11-23
|
The transverse breathing mode of an elongated Bose-Einstein condensate
|
We study experimentally the transverse monopole mode of an elongated rubidium
condensate. Due to the scaling invariance of the non-linear Schr\"odinger
(Gross-Pitaevski) equation, the oscillation is monochromatic and sinusoidal at
short times, even under strong excitation. For ultra-low temperatures, the
quality factor $Q=\omega_0/\gamma_0$ can exceed 2000, where $\omega_0$ and
$\gamma_0$ are the mode angular frequency and damping rate. This value is much
larger than any previously reported for other eigenmodes of a condensate. We
also present the temperature variation of $\omega_0$ and $\gamma_0$.
|
0111455v1
|
2002-01-08
|
Feromagnetic "$π$"-junctions
|
We investigate Josephson coupling through a ferromagnetic thin film using
Superconductor-Insulator-Ferromagnet-Superconductor planar junctions. Damped
oscillations of the critical current are observed as a function of the
ferromagnetic layer thickness. We show that they result from the exchange
energy gained or lost by a quasiparticle Andreev-reflected at the
ferromagnet-superconductor interface. The critical current cancels out at the
transition from positive ("0") to negative ("$\pi$") coupling, in agreement
with theoretical calculations.
|
0201104v2
|
2002-03-08
|
Exact c-number Representation of Non-Markovian Quantum Dissipation
|
The reduced dynamics of a quantum system interacting with a linear heat bath
finds an exact representation in terms of a stochastic Schr{\"o}dinger
equation. All memory effects of the reservoir are transformed into noise
correlations and mean-field friction. The classical limit of the resulting
stochastic dynamics is shown to be a generalized Langevin equation, and
conventional quantum state diffusion is recovered in the Born--Markov
approximation. The non-Markovian exact dynamics, valid at arbitrary temperature
and damping strength, is exemplified by an application to the dissipative
two-state system.
|
0203193v1
|
2002-05-01
|
Amplitude coda of classical waves in disordered media
|
The propagation of classical waves in the presence of a disordered medium is
studied. We consider wave pulses containing a broad range of frequencies in
terms of the configurationally averaged Green function of the system. Damped
oscillations in the time-dependent response trailing behind the direct arrival
of the pulse (coda) are predicted, the periods of which are governed by the
density of scatterers.
|
0205014v1
|
2002-05-14
|
Finite temperature spectral function of Mott insulators and CDW States
|
We calculate the low temperature spectral function of one-dimensional
incommensurate charge density wave (CDW) states and half-filled Mott insulators
(MI). At $T=0$ there are two dispersing features associated with the spin and
charge degrees of freedom respectively. We show that already at very low
temperatures (compared to the gap) one of these features gets severely damped.
We comment on implications of this result for photoemission experiments.
|
0205294v2
|
2002-07-26
|
Experimental Investigation of Microwave Enhanced Cotunneling in SET Transistors
|
Cotunneling is an important error process in the application of single
electron tunneling devices for metrological and electronic applications. Here
we present an experimental investigation of the theory for adiabatic
enhancement of cotunneling by coherent microwaves. The dependence is
investigated as function of temperature, gate voltage, frequency, and applied
microwave power. At low temperatures and applied power levels, the results are
consistent with theory, using only the unknown damping in the microwave line as
a free parameter. However, the results indicate that the effects of
temperature, frequency and microwave power are not independent, contrary to
what is suggested by theory.
|
0207639v1
|
2002-07-26
|
Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer
|
Charge transfer along the base-pair stack in DNA is modeled in terms of
thermally-assisted tunneling between adjacent base pairs. Central to our
approach is the notion that tunneling between fluctuating pairs is rate-limited
by the requirement of their optimal alignment. We focus on this aspect of the
process by modeling two adjacent base pairs in terms of a classical damped
oscillator subject to thermal fluctuations as described by a Fokker-Planck
equation. We find that the process is characterized by two time scales, a
result that is in accord with experimental findings.
|
0207654v1
|
2002-08-27
|
Sound Propagation in Nematic Fermi Liquid
|
We study the longitudinal sound propagation in the electronic nematic Fermi
liquid where the Fermi surface is distorted due to the spontaneously broken
rotational symmetry. The behavior of the sound wave in the nematic ordered
state is dramatically different from that in the isotropic Fermi liquid. The
collective modes associated with the fluctuations of the Fermi surface
distortion in the nematic Fermi liquid leads to the strong and anisotropic
damping of the sound wave. The relevance of the nematic Fermi liquid in doped
Mott insulator is discussed.
|
0208524v1
|
2002-09-06
|
Nonequilibrium Fluctuations and Decoherence in Nanomechanical Devices Coupled to the Tunnel Junction
|
We analyze the dynamics of a nanomechanical oscillator coupled to an
electrical tunnel junction with an arbitrary voltage applied to the junction
and arbitrary temperature of electrons in leads. We obtain the explicit
expressions for the fluctuations of oscillator position, its
damping/decoherence rate, and the current through the structure. It is shown
that quantum heating of the oscillator results in nonlinearity of the
current-voltage characteristics. The effects of mechanical vacuum fluctuations
are also discussed.
|
0209149v1
|
2002-09-09
|
Decoherence and Relaxation of a Quantum Bit in the Presence of Rabi Oscillations
|
Dissipative dynamics of a quantum bit driven by a strong resonant field and
interacting with a heat bath is investigated. We derive generalized Bloch
equations and find modifications of the qubit's damping rates caused by Rabi
oscillations. Nonequilibrium decoherence of a phase qubit inductively coupled
to a LC-circuit is considered as an illustration of the general results. It is
argued that recent experimental results give a clear evidence of effective
suppression of decoherence in a strongly driven flux qubit.
|
0209217v4
|
2002-09-10
|
Effective Field Theory for Goldstone Bosons in Nonrelativistic Superfluids
|
We consider nonrelativistic superfluids where the global U(1)-symmetry is
spontaneously broken. At sufficiently long wavelengths, the relevant degree of
freedom is the massless Goldstone mode and we construct an effective low energy
theory for the Goldstone boson. The damping rate of collective excitations at
low energy is calculated. In the case of a weakly interacting Bose gas, we
recover the results by Beliaev, and by Hohenberg and Martin.
|
0209243v1
|
2002-11-06
|
Quadrupole Oscillation of a Single-Vortex Condensate: Evidence for Kelvin Modes
|
We study the two transverse quadrupole modes of a cigar-shaped Bose-Einstein
condensate with a single centered vortex. We show that the counter-rotating
mode is more strongly damped than in the absence of a vortex, whereas the
co-rotating mode is not affected appreciably by the vortex. We interpret this
result as a decay of the counter-rotating quadrupole mode into two excitations
of the vortex line, the so-called Kelvin modes. This is supported by direct
observation of the wiggling vortex line.
|
0211101v1
|
2002-11-19
|
Beliaev Damping and Kelvin Mode Spectroscopy of a Condensate in the Presence of a Vortex Line
|
It is demonstrated theoretically that the counter-rotating quadrupole mode in
a vortex of Bose-Einstein condensates can decay into a pair of Kelvin modes via
Beliaev process. We calculate the spectral weight of density-response function
within Bogoliubov framework, taking account of both Beliaev and Landau
processes. Good agreement with experiment on $^{87}$Rb by Bretin et al.
[cond-mat/0211101] allows us to unambigiously identify the decayed mode as the
Kelvin wave propagating along a vortex line.
|
0211396v1
|
2002-11-20
|
Vortex dynamics in the nonlinear Schrodinger equation
|
The dynamics of a two-dimensional vortex are analyzed within the framework of
the nonlinear Schrodinger equation. Both a bare vortex and a vortex with an
external mass trapped in a finite-sized core are considered. The bare vortex
motion is found to be damped at all frequencies, while the finite core has a
single resonant frequency. The force exerted by the fluid on the finite core
can be expressed as a sum of dissipative and Magnus forces for sufficiently low
frequencies, even when the core is small.
|
0211424v1
|
2002-12-05
|
Activated escape over oscillating barriers: The case of many dimensions
|
We present a novel path-integral method for the determination of
time-dependent and time-averaged reaction rates in multidimensional,
periodically driven escape problems at weak thermal noise. The so obtained
general expressions are evaluated explicitly for the situation of a
sinusoidally driven, damped particle with inertia moving in a metastable,
piecewise parabolic potential. A comparison with data from Monte-Carlo
simulations yields a very good agreement with our analytic results over a wide
parameter range.
|
0212117v1
|
2002-12-05
|
Dynamic stiffness of spin valves
|
The dynamics of the magnetic order parameters of
ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may
be very different. We investigate the role of the nonequilibrium spin-current
exchange between the ferromagnets in the magnetization precession and
switching. We find a (low-temperature) critical current bias for a coherent
current-induced magnetization excitation in spin valves, which unifies and
generalizes previous ideas of Slonczewski and Berger. In the absence of an
applied bias, the effect of the spin transfer can be expressed as
magnetic--configuration-dependent Gilbert damping.
|
0212130v2
|
2003-01-15
|
Effects of parametric noise on a nonlinear oscillator
|
We study a model of a nonlinear oscillator with a random frequency and derive
the asymptotic behavior of the probability distribution function when the noise
is white. In the small damping limit, we show that the physical observables
grow algebraically with time before the dissipative time scale is reached, and
calculate the associated anomalous diffusion exponents. In the case of colored
noise, with a nonzero but arbitrarily small correlation time, the
characteristic exponents are modified. We determine their values thanks to a
self-consistent Ansatz.
|
0301259v1
|
2003-01-30
|
Quantum critical point in CuGeO3 doped with magnetic impurities
|
Using high frequency (up to 450 GHz) ESR and low temperature specific heat
measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and
Neel transitions and for T<30K gives rise to onset of a quantum critical
behaviour characteristic for a random dimer Griffiths phase.
|
0301595v1
|
2003-02-13
|
Steering of a Bosonic Mode with a Double Quantum Dot
|
We investigate the transport and coherence properties of a double quantum dot
coupled to a single damped boson mode. Our numerically results reveal how the
properties of the boson distribution can be steered by altering parameters of
the electronic system such as the energy difference between the dots.
Quadrature amplitude variances and the Wigner function are employed to
illustrate how the state of the boson mode can be controlled by a stationary
electron current through the dots.
|
0302265v1
|
2003-02-18
|
Flow equation renormalization of a spin-boson model with a structured bath
|
We discuss the dynamics of a spin coupled to a damped harmonic oscillator.
This system can be mapped to a spin-boson model with a structured bath, i.e.
the spectral function of the bath has a resonance peak. We diagonalize the
model by means of infinitesimal unitary transformations (flow equations),
thereby decoupling the small quantum system from its environment, and calculate
spin-spin correlation functions.
|
0302357v1
|
2003-03-28
|
Models for generation 1/f noise
|
Simple analytically solvable models are proposed exhibiting 1/f spectrum in
wide range of frequency. The signals of the models consist of pulses (point
process) which interevent times fluctuate about some average value, obeying an
autoregressive process with very small damping. The power spectrum of the
process can be expressed by the Hooge formula. The proposed models reveal
possible origin of 1/f noise, i.e., random increments of the time intervals
between pulses or interevent time of the process (Brownian motion in the time
axis).
|
0303603v1
|
2003-04-08
|
Exploiting environmental resonances to enhance qubit quality factors
|
We discuss dephasing times for a two-level system (including bias) coupled to
a damped harmonic oscillator. This system is realized in measurements on
solid-state Josephson qubits. It can be mapped to a spin-boson model with a
spectral function with an approximately Lorentzian resonance. We diagonalize
the model by means of infinitesimal unitary transformations (flow equations),
and calculate correlation functions, dephasing rates, and qubit quality
factors. We find that these depend strongly on the environmental resonance
frequency $\Omega$; in particular, quality factors can be enhanced
significantly by tuning $\Omega$ to lie below the qubit frequency $\Delta$.
|
0304177v1
|
2003-05-08
|
Resonant nature of phonon-induced damping of Rabi oscillations in quantum dots
|
Optically controlled coherent dynamics of charge (excitonic) degrees of
freedom in a semiconductor quantum dot under the influence of lattice dynamics
(phonons) is discussed theoretically. We show that the dynamics of the lattice
response in the strongly non-linear regime is governed by a semiclassical
resonance between the phonon modes and the optically driven dynamics. We stress
on the importance of the stability of intermediate states for the truly
coherent control.
|
0305165v2
|
2003-05-23
|
Phase field approach for modeling intracellular dynamics
|
We introduce a phase field approach for diffusion inside and outside a closed
cell with damping and with source terms at the interface. The method is
compared to exact solutions (where possible) and the more traditional finite
element method. It is shown to be very accurate, easy to implement and
computationally inexpensive. We apply our method to a recently introduced model
for chemotaxis by Rappel et al. [Biophys. J. 83, 1361 (2002)].
|
0305577v1
|
2003-06-11
|
Phase locking in quantum and classical oscillators: polariton condensates, lasers, and arrays of Josephson junctions
|
We connect three phenomena in which a coherent electromagnetic field could be
generated: polariton condensation, phase-locking in arrays of underdamped
Josephson junctions, and lasing. All these phenomena have been described using
Dicke-type models of spins coupled to a single photon mode. These descriptions
may be distinguished by whether the spins are quantum or classical, and whether
they are strongly or weakly damped.
|
0306268v1
|
2003-06-26
|
Nanoscience with Attosecond Laser Pulses
|
In this paper the interaction of attosecond laser pulses with matter is
investigated. The scattering and potential motion of heat carriers as well as
the external force are considered. Depending on the ratio of the scatterings
and potential motion the heat transport is described by the thermal forced
Klein-Gordon or thermal modified telegraph equation. For thermal Heisenberg
type relation V tau=hbar (tau is the relaxation time and V is the potential)
the heat transport is described by the thermal distortionless damped wave
equation. In this paper Klein-Gordon modified telegraph equation and wave
equation are solved. Key words: Attosecond laser pulses; Quantum heat transport
equation; Klein-Gordon thermal equation.
|
0306671v1
|
2003-06-27
|
Origin of the "Waterfall" Effect in Phonon Dispersion of Relaxor Perovskites
|
Inelastic neutron scattering study of the perovskite relaxor ferroelectric
PZN:8%PT elucidates the origin of the previously reported unusual kink on the
low frequency transverse phonon dispersion curve (known as "waterfall" effect).
We show that its position depends on the choice of the Brillouin zone and that
the relation of its position to the size of the polar nanoregions is highly
improbable. The observation is explained in the framework of a simple model of
coupled damped harmonic oscillators representing the acoustic and optic phonon
branches.
|
0306692v1
|
2003-07-04
|
Comment on "Estimate of the vibrational frequencies of spherical virus particles"
|
This comment corrects some errors which appeared in the calculation of an
elastic sphere eigenenergies. As a result, the symmetry of the mode having the
lowest frequency is changed. Also a direction for calculating the damping of
these modes for embedded elastic spheres is given.
|
0307112v2
|
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