2,010 research outputs found
Time-reversal symmetry breaking by ac field: Effect of commensurability in the frequency domain
It is shown that the variance of the linear dc conductance fluctuations in an
open quantum dot under a high-frequency ac pumping depends significantly on the
spectral content of the ac field. For a sufficiently strong ac field the dc
conductance fluctuations are much stronger for the periodic pumping than in the
case of the noise ac field of the same intensity. The reduction factor r in a
static magnetic field takes the universal value of 2 only for the white-noise
pumping. In general r may deviate from 2 thus signalling on the time-reversal
symmetry breaking by the ac field. For the bi-harmonic ac field of the form
A(t)=A_{0} [cos(\omega_{1} t)+cos(\omega_{2} t)] we predict the enchancement of
effects of T-symmetry breaking at commensurate frequencies
\omega_{2}/\omega_{1}=P/Q. In the high-temperature limit there is also the
parity effect: the enchancement is only present if either P or Q is even.Comment: 8 pages, 6 figures, submitted for "Electronic Correlations: from
meso- to nano-physics", edited by G. Montambaux and T. Martin, Rencontres de
Morion
Energy level statistics of a critical random matrix ensemble
We study level statistics of a critical random matrix ensemble of a power-law
banded complex Hermitean matrices. We compute numerically the level
compressibility via the level number variance and compare it with the
analytical formula for the exactly solvable model of Moshe, Neuberger and
Shapiro.Comment: 8 pages, 3 figure
Two-eigenfunction correlation in a multifractal metal and insulator
We consider the correlation of two single-particle probability densities
at coinciding points as a function of the
energy separation for disordered tight-binding lattice models
(the Anderson models) and certain random matrix ensembles. We focus on the
models in the parameter range where they are close but not exactly at the
Anderson localization transition. We show that even far away from the critical
point the eigenfunction correlation show the remnant of multifractality which
is characteristic of the critical states. By a combination of the numerical
results on the Anderson model and analytical and numerical results for the
relevant random matrix theories we were able to identify the Gaussian random
matrix ensembles that describe the multifractal features in the metal and
insulator phases. In particular those random matrix ensembles describe new
phenomena of eigenfunction correlation we discovered from simulations on the
Anderson model. These are the eigenfunction mutual avoiding at large energy
separations and the logarithmic enhancement of eigenfunction correlations at
small energy separations in the two-dimensional (2D) and the three-dimensional
(3D) Anderson insulator. For both phenomena a simple and general physical
picture is suggested.Comment: 16 pages, 18 figure
Statistics of Green's functions on a disordered Cayley tree and the validity of forward scattering approximation
The accuracy of the forward scattering approximation for two-point Green's functions of the Anderson localization model on the Cayley tree is studied. A relationship between the moments of the Green's function and the largest eigenvalue of the linearized transfer-matrix equation is proved in the framework of the supersymmetric functional-integral method. The new large-disorder approximation for this eigenvalue is derived and its accuracy is established. Using this approximation the probability distribution of the two-point Green's function is found and compared with that in the forward scattering approximation (FSA). It is shown that FSA overestimates the role of resonances and thus the probability for the Green's function to be significantly larger than its typical value. The error of FSA increases with increasing the distance between points in a two-point Green's function
Limits of the dynamical approach to non-linear response of mesoscopic systems
We have considered the nonlinear response of mesoscopic systems of
non-interacting electrons to the time-dependent external field. In this
consideration the inelastic processes have been neglected and the electron
thermalization occurs due to the electron exchange with the reservoirs. We have
demonstrated that the diagrammatic technique based on the method of analytical
continuation or on the Keldysh formalism is capable to describe the heating
automatically. The corresponding diagrams contain a novel element, {\it the
loose diffuson}. We have shown the equivalence of such a diagrammatic technique
to the solution to the kinetic equation for the electron energy distribution
function. We have identified two classes of problems with different behavior
under ac pumping. In one class of problems (persistent current fluctuations,
Kubo conductance) the observable depends on the electron energy distribution
renormalized by heating. In another class of problems (Landauer conductance)
the observable is insensitive to heating and depends on the temperature of
electron reservoirs. As examples of such problems we have considered in detail
the persistent current fluctuations under ac pumping and two types of
conductance measurements (Landauer conductance and Kubo conductance) that
behave differently under ac pumping.Comment: 21 pages, RevTex, 10 eps.figures; final version to appear in
Phys.Rev.
Change of cosmic ray anisotropy with solar activity
Muon telescope data at various depths underground in Yakutsk within energy range 10 to 300 GeV for 1957 to 1984 are analyzed. The 22-year variation of the interplanetary magnetic field aligned component is found. The variation is caused by interaction of heliomagnetosphere with the local galactic field and interstellar wind
Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma
Equations describing the linear evolution of a non-dissipative Langmuir wave
in inhomogeneous nonstationary anisotropic plasma without magnetic field are
derived in the geometrical optics approximation. A continuity equation is
obtained for the wave action density, and the conditions for the action
conservation are formulated. In homogeneous plasma, the wave field E
universally scales with the electron density N as E ~ N^{3/4}, whereas the
wavevector evolution varies depending on the wave geometry
Space-frequency correlation of classical waves in disordered media: high-frequency and small scale asymptotics
Two-frequency radiative transfer (2f-RT) theory is developed for geometrical
optics in random media. The space-frequency correlation is described by the
two-frequency Wigner distribution (2f-WD) which satisfies a closed form
equation, the two-frequency Wigner-Moyal equation. In the RT regime it is
proved rigorously that 2f-WD satisfies a Fokker-Planck-like equation with
complex-valued coefficients. By dimensional analysis 2f-RT equation yields the
scaling behavior of three physical parameters: the spatial spread, the
coherence length and the coherence bandwidth. The sub-transport-mean-free-path
behavior is obtained in a closed form by analytically solving a paraxial 2f-RT
equation
Role of divergence of classical trajectories in quantum chaos
We study logarithmical in effects in the statistical description of
quantum chaos. We found analytical expressions for the deviations from the
universality in the weak localization corrections and the level statistics and
showed that the characteristic scale for these deviations is the Ehrenfest
time, , where is the Lyapunov exponent
of the classical motion.Comment: 4 pages, no figure
- …