arXiv subjects

A. D. Zaikin

Publications and source records attributed to A. D. Zaikin.

45 records · Page 3Linked to original sources

arXiv1996

Ballistic Transport in Superconducting Weak Links in a Microwave Field

Nonequilibrium effects and their impact on a charge transport in superconducting ballistic weak links biased by an ac voltage are investigated within the framework of the Keldysh technique. We demonstrate that the microwave field destroys the phase coherence during the multiple Andreev reflection cycle and leads to the effective cooling of subgap quasiparticles accelerated due to multiple Andreev reflection. For small bias voltages this effect results in a strong supression of both the excess current and the conductance of the weak link. In the opposite limit of large bias voltages the excess current remains unaffected. We also demonstrate that a simple Boltzmann kinetic approach becomes inadequate if an ac voltage bias is applied to the weak link.

cond-mat.supr-con↗

arXiv1996

Strong Electron Tunneling through a Small Metallic Grain

Electron tunneling through mesoscopic metallic grains can be treated perturbatively only provided the tunnel junction conductances are sufficiently small. If it is not the case, fluctuations of the grain charge become strong. As a result (i) contributions of all -- including high energy -- charge states become important and (ii) excited charge states become broadened and essentially overlap. At the same time the grain charge remains discrete and the system conductance $e$-periodically depends on the gate charge. We develop a nonperturbative approach which accounts for all these features and calculate the temperature dependent conductance of the system in the strong tunneling regime at different values of the gate charge.

cond-mat↗

arXiv1996

Coherent Charge Transport in Metallic Proximity Structures

We develop a detailed microscopic analysis of electron transport in normal diffusive conductors in the presence of proximity induced superconducting correlation. We calculated the linear conductance of the system, the profile of the electric field and the densities of states. In the case of transparent metallic boundaries the temperature dependent conductance has a non-monotoneous ``reentrant'' structure. We argue that this behavior is due to nonequilibrium effects occuring in the normal metal in the presence of both superconducting correlations and the electric field there. Low transparent tunnel barriers suppress the nonequilibrium effects and destroy the reentrant behavior of the conductance. If the wire contains a loop, the conductance shows Aharonov-Bohm oscillations with the period $Φ_0=h/2e$ as a function of the magnetic flux $Φ$ inside the loop. The amplitude of these oscillations also demonstrates the reentrant behavior vanishing at $T=0$ and decaying as $1/T$ at relatively large temperatures. The latter behavior is due to low energy correlated electrons which penetrate deep into the normal metal and ``feel'' the effect of the magnetic flux $Φ$. We point out that the density of states and thus the ``strengh'' of the proximity effect can be tuned by the value of the flux inside the loop. Our results are fully consistent with recent experimental findings.

cond-mat↗

arXiv1996

Coherent transport in a normal diffusive wire between two reservoirs

We develop a detailed analysis of electron transport in normal diffusive con- ductors in the presence of proximity induced superconductivity. A rich structure of temperature and energy dependencies for the system condcutcance, density of states and related quantities was found and explained. If the nor- mal conductor forms a loop its conductance changes h/2e-periodically with the magnetic flux inside the loop. The amplitude of these conductance oscillations shows a reentrant behavior and decays as 1/T at high T

cond-mat↗

arXiv1996

Charge Transport in Superconductor - Normal Metal Proximity Structures

We develop a detailed analysis of electron transport in normal diffusive conductors in the presence of proximity induced superconducting correlation. We calculated the linear conductance of the system and the profile of the electric field. A rich structure of temperature dependences was found and explained. Our results are consistent with recent experimental findings.

cond-mat↗

arXiv1995

Charge Disorder in Granular Metallic Films

It is shown that practically any physically relevant random distribution of offset charges destroys the Kosterlitz-Thouless-Berezinskii charge-unbinding phase transition in two dimensional normal and superconducting granular arrays and films. The array conductance obeys the Arrenius dependence on temperature. Offset charge disorder decreases the effective Coulomb gap of the system and may account for recent experimental findings in two dimensional arrays of tunnel junctions.

cond-mat↗

arXiv1995

"Chain scenario" for Josephson tunneling with pi-shift in YBa2Cu3O7

We point out that all current Josephson-junction experiments probing directly the symmetry of the superconducting state in YBa2Cu3O7, can be interpreted in terms of the bilayer antiferromagnetic spin fluctuation model, which renders the superconducting state with the order parameters of extended $s$ symmetry, but with the opposite signs in the bonding and antibonding Cu-O plane bands. The essential part of our interpretation includes the Cu-O chain band which would have the order parameter of the same sign as antibonding plane band. We show that in this case net Josephson currents along and perpendicular to the chains have the phase shift equal to pi.

cond-mat↗

arXiv1994

Charge Transport in Junctions between D-Wave Superconductors

We develop a microscopic analysis of superconducting and dissipative currents in junctions between superconductors with d-wave symmetry of the order parameter. We study the proximity effect in such superconductors and show that for certain crystal orientations the superconducting order parameter can be essentially suppressed in the vicinity of a nontransparent specularly reflecting boundary. This effect strongly influences the value and the angular dependence of the dc Josephson current $j_S$. At $T \sim T_c $ it leads to a crossover between $j_S \propto T_c-T$ and $j_S \propto (T_c-T)^2$ respectively for homogeneous and nonhomogeneous distribution of the order parameter in the vicinity of a tunnel junction. We show that at low temperatures the current-phase relation $j_S(φ)$ for SNS junctions and short weak links between d-wave superconductors is essentially nonharmonic and contains a discontinuity at $φ=0$. This leads to further interesting features of such systems which can be used for novel pairing symmetry tests in high temperature superconductors (HTSC). We also investigated the low temperature I-V curves of NS and SS tunnel junctions and demonstrated that depending on the junction type and crystal orientation these curves show zero-bias anomalies $I\propto V^2$, $I\propto V^2\ln (1/V)$ and $I\propto V^3$ caused by the gapless behavior of the order parameter in d-wave superconductors. Many of our results agree well with recent experimental findings for HTSC compounds.

cond-mat↗

arXiv1993

Parity Effects on Electron Tunneling through Small Superconducting Islands

Single electron tunneling into small superconducting islands is sensitive to the gap energy of the excitations created in the process and, hence, depends on the electron number parity. At low temperature the properties of the system are 2e-periodic in the applied gate voltage, turning e-periodic at higher temperature. We evaluate the tunneling rates and determine the probabilities for the even and odd state as well as the cross-over condition from the balance between different processes. Our analysis includes excitations in the leads. They are essential if the leads are superconducting. The influence of parity effects on single electron tunneling, Cooper pair tunneling, and the Andreev reflection in superconducting transistors yields rich structures in the I-V characteristic, which explains recent experimental findings.

cond-mat↗