Landau damping: instability mechanism of superfluid Bose gases moving in optical lattices

TL;DR

This paper analyzes the Landau damping mechanism in superfluid Bose gases within optical lattices, linking the damping rate to superfluid stability and critical velocities, and connecting microscopic processes to experimental observations.

Contribution

It provides an explicit calculation of Landau damping rates in a 1D lattice model, revealing the microscopic origin of superfluid instability and its relation to the Landau criterion.

Findings

Sign change in damping rate at critical velocity

Microscopic mechanism of Landau instability identified

Thermal cloud influences superfluid breakdown

Abstract

We investigate Landau damping of Bogoliubov excitations in a dilute Bose gas moving in an optical lattice at finite temperatures. Using a 1D tight-binding model, we explicitly obtain the Landau damping rate, the sign of which determines the stability of the condensate. We find that the sign changes at a certain condensate velocity, which is exactly the same as the critical velocity determined by the Landau criterion of superfluidity. This coincidence of the critical velocities reveals the microscopic mechanism of the Landau instability. This instability mechanism is also consistent with the recent experiment suggesting that a thermal cloud plays a crucial role in breakdown of superfluids, since the thermal cloud is also vital in the Landau damping process. We also examine the possibility of simultaneous disappearance of all damping processes.