Far-from-equilibrium dynamics of spin-orbit coupled superfluids

Maxim Dzero, Ammar A. Kirmani, Emil A. Yuzbashyan

We study a problem of nonadiabatic superfluid dynamics of spin-orbit-coupled neutral fermions in two spatial dimensions. We focus on the two cases when the out-of-equilibrium conditions are initiated by either a sudden change of the pairing strength or the population imbalance. For the case of a zero-population imbalance and within the mean-field approximation, the nonadiabatic evolution of the pairing amplitude in a collisionless regime can be found exactly by employing the method of Lax vector construction. Our main finding is that the presence of the spin-orbit coupling significantly reduces the region in the parameter space where a steady state with periodically oscillating pairing amplitude is realized. For the collisionless dynamics initiated by a sudden disappearance of the population imbalance, we obtain an exact expression for the steady-state pairing amplitude. In the general case of quenches to a state with finite population imbalance, we show that there is a region in the steady-state phase diagram where at long times the pairing amplitude dynamics is governed by the reduced number of the equations of motion in full analogy with the exactly integrable case.

Marine Pigneur

Shuning Tan, Jiayi Shi, Peng Zou +2 more

Abstract Exploring anisotropic dynamics in exotic superconductors or superfluids with spin–orbit coupling (SOC) is essential for understanding the role of SOC in these systems. We theoretically calculate the density dynamical structure factor of a two-dimensional Fermi superfluid with Raman-type SOC and investigate its primary anisotropic dynamical characteristics under varying SOC strengths during the Lifshitz phase transition. Owing to the recoil momentum of the SOC laser beam, both the collective phonon mode and the single-particle excitations exhibit distinct anisotropic behavior. In contrast to superfluids without SOC, the phonon mode under SOC not only has a shorter lifetime due to stronger competition with single-particle excitations but also exhibits an anisotropic sound velocity. The sound velocity initially decreases and then increases as the SOC strength increases. Moreover, three types of threshold energies for single-particle excitations to break Cooper pairs are identified, which elucidate the complex edge curves of the dynamical structure factor.

Chuanzhou Zhu, Li Chen, Han Pu

F. Setiawan, K. Sengupta, Ian B. Spielman +1 more

We demonstrate that non-equilibrium dynamics provides a direct means of detecting the topological phase transition (TPT) between conventional and topological superfluid (SF) phases in one-dimensional spin-orbit-coupled Fermi gases with attractive interactions. To date, no cold atom experiment has realized a topological SF, because of loss or heating processes. In the alkali fermions, off-resonant light scattering dominates these processes, therefore, we minimize their impact by rapidly quenching in and out of the topological SF phase. This quench excites Bogoliubov quasiparticles in the final phase (a conventional SF), the distribution of which carries signatures of the TPT. We calculate the resulting spin-resolved momentum distribution by self-consistently solving the time-dependent Bogoliubov-de Gennes equations. They exhibit Kibble-Zurek scaling and St\{u}ckelberg oscillations characteristic of the TPT. We discuss parameter regimes where the TPT is experimentally accessible.