448 research outputs found

### Fingerprints of classical diffusion in open 2D mesoscopic systems in the metallic regime

We investigate the distribution of the resonance widths ${\cal P}(\Gamma)$
and Wigner delay times ${\cal P}(\tau_W)$ for scattering from two-dimensional
systems in the diffusive regime. We obtain the forms of these distributions
(log-normal for large $\tau_W$ and small $\Gamma$, and power law in the
opposite case) for different symmetry classes and show that they are determined
by the underlying diffusive classical dynamics. Our theoretical arguments are
supported by extensive numerical calculations.Comment: 7 pages, 3 figure

### Scattering approach to Anderson localization

We develop a novel approach to the Anderson localization problem in a d-dimensional disordered sample of dimension LÃ—Mdâˆ’1. Attaching a perfect lead with the cross section Mdâˆ’1 to one side of the sample, we derive evolution equations for the scattering matrix and the Wigner-Smith time delay matrix as a function of L. Using them one obtains the Fokker-Planck equation for the distribution of the proper delay times and the evolution equation for their density at weak disorder. The latter can be mapped onto a nonlinear partial differential equation of the Burgers type, for which a complete analytical solution for arbitrary L is constructed. Analyzing the solution for a cubic sample with M=L in the limit Lâ†’âˆž, we find that for d2 to the metallic fixed point, and provide explicit results for the density of the delay times in these two limits

### Entanglement entropy in Fermi gases and Anderson's orthogonality catastrophe

We study the ground-state entanglement entropy of a finite subsystem of size L of an infinite system of noninteracting fermions scattered by a potential of finite range a. We derive a general relation between the scattering matrix and the overlap matrix and use it to prove that for a one-dimensional symmetric potential the von Neumann entropy, the RÃ©nyi entropies, and the full counting statistics are robust against potential scattering, provided that L/aâ‰«1. The results of numerical calculations support the validity of this conclusion for a generic potential

### Level number variance and spectral compressibility in a critical two-dimensional random matrix model

We study level number variance in a two-dimensional random matrix model
characterized by a power-law decay of the matrix elements. The amplitude of the
decay is controlled by the parameter b. We find analytically that at small
values of b the level number variance behaves linearly, with the
compressibility chi between 0 and 1, which is typical for critical systems. For
large values of b, we derive that chi=0, as one would normally expect in the
metallic phase. Using numerical simulations we determine the critical value of
b at which the transition between these two phases occurs.Comment: 6 page

### Reentrance effect in a graphene n-p-n junction coupled to a superconductor

We study the interplay of Klein tunneling (= interband tunneling) between
n-doped and p-doped regions in graphene and Andreev reflection (= electron-hole
conversion) at a superconducting electrode. The tunneling conductance of an
n-p-n junction initially increases upon lowering the temperature, while the
coherence time of the electron-hole pairs is still less than their lifetime,
but then drops back again when the coherence time exceeds the lifetime. This
reentrance effect, known from diffusive conductors and ballistic quantum dots,
provides a method to detect phase coherent Klein tunneling of electron-hole
pairs.Comment: 4 pages, 3 figure

### How spin-orbit interaction can cause electronic shot noise

The shot noise in the electrical current through a ballistic chaotic quantum
dot with N-channel point contacts is suppressed for N --> infinity, because of
the transition from stochastic scattering of quantum wave packets to
deterministic dynamics of classical trajectories. The dynamics of the electron
spin remains quantum mechanical in this transition, and can affect the
electrical current via spin-orbit interaction. We explain how the role of the
channel number N in determining the shot noise is taken over by the ratio
l_{so}/lambda_F of spin precession length l_{so} and Fermi wave length
lambda_F, and present computer simulations in a two-dimensional billiard
geometry (Lyapunov exponent alpha, mean dwell time tau_{dwell}, point contact
width W) to demonstrate the scaling (lambda_F/l_{so})^{1/alpha tau_{dwell}} of
the shot noise in the regime lambda_F << l_{so} << W.Comment: 4 pages, 3 figure

### Localization-delocalization transition in the quasi-one-dimensional ladder chain with correlated disorder

The generalization of the dimer model on a two-leg ladder is defined and
investigated both, analytically and numerically. For the closed system we
calculate the Landauer resistance analytically and found the presence of the
point of delocalization at the band center which is confirmed by the numerical
calculations of the Lyapunov exponent. We calculate also analytically the
localization length index and present the numerical investigations of the
density of states (DOS). For the open counterpart of this model the
distribution of the Wigner delay times is calculated numerically. It is shown
how the localization-delocalization transition manifest itself in the behavior
of the distribution.Comment: 9 pages, 10 figures, Revte

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