Berezinskii-Kosterlitz-Thouless scaling in a Josephson junction of an ultracold two-dimensional Bose gas

Venue: Povo Zero, via Sommarive 14 (Povo) – Theoretical Physics Seminar room (second floor)
At: 10.30

Dr. Vijay Singh - Zentrum fuer Optische Quantentechnologien and Institut fuer Laserphysik, Universitaet Hamburg

Abstract:

We investigate the Berezinskii-Kosterlitz-Thouless (BKT) scaling of the critical current of a Josephson junction of an ultracold two-dimensional (2D) Bose gas using classical-field dynamics.
We examine the supercurrent dynamics across the Josephson junction of two 2D clouds separated by a tunneling barrier. We find that the tunneling dynamics is influenced by the bulk dynamics, and the ideal junction (BJJ) dynamics is reached only for strong barrier heights compared to the mean-field energy. We map out various dynamical regimes as a function of the barrier height, and the temperature of the system, and identify the BJJ regime by the nonlinear current-phase relation
of an ideal Josephson junction. We derive an analytical estimate of the critical current, which shows good agreement to the simulations, and the experiments by Niclas et al. arXiv:1908.09776 (2019).
We extract the BKT scaling exponent from the critical current densities that are simulated at various system lengths and temperatures. We demonstrate that the exponents of the critical current density are in good agreement with the exponents of the equilibrium systems across the transition.
Furthermore, we address the damping of the current and identify the damping mechanism which is due to phonon excitations in the bulk, and the nucleation of vortex-antivortex pairs in the junction.

Scientific Coordinator: prof. Sandro Stringari