arXiv subjects

M. Titov

Publications and source records attributed to M. Titov.

96 records · Page 6Linked to original sources

arXiv2001

Can mesoscopic fluctuations reverse the supercurrent through a disordered Josephson junction?

We calculate the Josephson coupling energy $U_J(ϕ)$ (related to the supercurrent $I=(2e/\hbar) dU_J/dϕ$) for a disordered normal metal between two superconductors with a phase difference $ϕ$. We demonstrate that the symmetry of the scattering matrix of non-interacting quasiparticles in zero magnetic field implies that $U_J(ϕ)$ has a minimum at $ϕ=0$. A maximum (that would lead to a $π$-junction or negative superfluid density) is excluded for any realization of the disorder.

cond-mat.mes-hall↗

arXiv2001

Andreev levels in a single-channel conductor

We calculate the subgap density of states of a disordered single-channel normal metal connected to a superconductor at one end (NS junction) or at both ends (SNS junction). The probability distribution of the energy of a bound state (Andreev level) is broadened by disorder. In the SNS case the two-fold degeneracy of the Andreev levels is removed by disorder leading to a splitting in addition to the broadening. The distribution of the splitting is given precisely by Wigner's surmise from random-matrix theory. For strong disorder the mean density of states is largely unaffected by the proximity to the superconductor, because of localization, except in a narrow energy region near the Fermi level, where the density of states is suppressed with a log-normal tail.

cond-mat.mes-hall↗

arXiv2001

Fokker-Planck equations and density of states in disordered quantum wires

We propose a general scheme to construct scaling equations for the density of states in disordered quantum wires for all ten pure Cartan symmetry classes. The anomalous behavior of the density of states near the Fermi level for the three chiral and four Bogoliubov-de Gennes universality classes is analysed in detail by means of a mapping to a scaling equation for the reflection from a quantum wire in the presence of an imaginary potential.

cond-mat.dis-nn↗

arXiv2000

Signature of wave localisation in the time dependence of a reflected pulse

The average power spectrum of a pulse reflected by a disordered medium embedded in an N-mode waveguide decays in time with a power law t^(-p). We show that the exponent p increases from 3/2 to 2 after N^2 scattering times, due to the onset of localisation. We compare two methods to arrive at this result. The first method involves the analytic continuation to imaginary absorption rate of a static scattering problem. The second method involves the solution of a Fokker-Planck equation for the frequency dependent reflection matrix, by means of a mapping onto a problem in non-Hermitian quantum mechanics.

cond-mat.dis-nn↗

arXiv1998

Design and Operation of Front-End Electronics for the HERA-B Muon Detector

We have implemented a cost-effective design for the readout electronics of both the anode wires and the cathode pads of large area proportional wire chambers for the HERA-B muon system based on the ASD-08 integrated circuit. To control and monitor the large number of readout channels, we have built a distributed control system based on Philips Semiconductors' I2C bus and microcontrollers. To date we have installed about 10800 channels of muon chambers and electronics. The average single channel noise occupancy is less than 10**-5, and the detectors have been operated with target interaction rates as high as 70 MHz.

physics.ins-det↗

arXiv1998

S-matrix poles for chaotic quantum systems as eigenvalues of complex symmetric random matrices: from isolated to overlapping resonances

We study complex eigenvalues of large $N\times N$ symmetric random matrices of the form ${\cal H}=\hat{H}-i\hatΓ$, where both $\hat{H}$ and $\hatΓ$ are real symmetric, $\hat{H}$ is random Gaussian and $\hatΓ$ is such that $NTr \hatΓ^2_2\sim Tr \hat{H}_1^2$ when $N\to \infty$. When $\hatΓ\ge 0$ the model can be used to describe the universal statistics of S-matrix poles (resonances) in the complex energy plane. We derive the ensuing distribution of the resonance widths which generalizes the well-known $χ^2$ distribution to the case of overlapping resonances. We also consider a different class of "almost real" matrices when $\hatΓ$ is random and uncorrelated with $\hat{H}$.

chao-dyn↗