BCS quasi-particle tunnelling current in Josephson tunnel junctions

V. Gubankov, K. Y. Constantinian, V. P. Koshelets +2 more

The electrophysics and microwave properties of Niobium oxide-barrier tunnel junctions with critical current densities up to 105A/cm2were studied. Millimeter wave mixing using strong nonlinearity of quasi-particle tunnelling curve is described. Nonhysteretic Josephson junctions obtained by the low inductance resistive shunting of the tunnel structures were investigated in the large frequency band. The frequency range where these junctions obey the resistively shunted junction model was determined. The shunted tunnel junctions have been shown to be suitable for various applications which require stable enough Josephson junctions with nonhysteretic I-V curve (IVC).

J.T. Chen

Tharanga Jinasundera, Christoph Weiß, Martin Holthaus

Forrest C. Sheldon, Sebastiano Peotta, Massimiliano Di Ventra

In addition to the usual superconducting current, Josephson junctions (JJs) support a phase-dependent conductance related to the retardation effect of tunneling quasi-particles. This introduces a dissipative current with a memory-resistive (memristive) character that should also affect the current noise. By means of the microscopic theory of tunnel junctions we compute the complete current autocorrelation function of a Josephson tunnel junction and show that this memristive component gives rise to both a previously noted phase-dependent thermal noise, and an undescribed non-stationary, phase-dependent dynamic noise. As experiments are approaching ranges in which these effects may be observed, we examine the form and magnitude of these processes. Their phase dependence can be realized experimentally as a hysteresis effect and may be used to probe defects present in JJ based qubits and in other superconducting electronics applications.

Jon Links, Katrina Hibberd

Anonymous, Hiroyuki Tajima

We theoretically study the Josephson effect in ultracold Fermi gases, where the two sides of the Josephson junction are independently tuned to different regions of the Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein condensation (BEC) crossover. Using the nonequilibrium Green's function approach combined with the tunnel Hamiltonian formalism and a mean-field approach, we evaluate the DC and AC Josephson currents throughout the entire crossover region. We calculate the DC Josephson current as a function of interaction strength by tuning both sides of the junction synchronously from the BCS to the BEC regimes, and give the asymptotic expression of the current in the deep BCS and BEC limits. We also study the AC Josephson junction through the interaction-asymmetric junction by fixing the interaction in one reservoir and tuning that of the other one. A peak of the tunneling current is found when one side is fixed in the BCS limit and the other side is tuned into the BEC regime, which corresponds to the interaction-biased Riedel peak. Our results indicate the competition between contributions of increasing pair spectral weight and decreasing chemical potential to Josephson tunneling throughout the BCS-BEC crossover, and demonstrate the realization of the Riedel peak in strong-coupling quantum gases.