Odd-parity effect and scale-dependent viscosity in atomic quantum gases

TL;DR

This paper demonstrates that two-component atomic Fermi gases exhibit an odd-parity long-lived mode effect similar to electron gases, with tunable properties across the BCS-BEC crossover, affecting their collective oscillation damping.

Contribution

It establishes the presence of odd-parity long-lived modes in neutral atomic Fermi gases and explores their tunability and experimental signatures.

Findings

Odd-parity modes have long lifetimes below 0.15T_F.

The odd-even effect is tunable across the BCS-BEC crossover.

Enhanced damping of quadrupole oscillations indicates long-lived odd modes.

Abstract

Two-dimensional electron gases are predicted to possess an anomalous ''tomographic'' transport regime that is marked by an odd-even effect in the relaxation times, with odd-parity deformations of the Fermi surface becoming long-lived in comparison to even-parity ones. In this work, we establish that neutral two-component atomic Fermi gases also exhibit this tomographic effect. By diagonalizing the Fermi liquid collision integral, we identify odd-parity modes with anomalously long lifetimes below temperatures $T\leq 0.15T_F$, which is within reach of cold atom experiments. Furthermore, in contrast to electron gases, we find that the odd-even effect in neutral gases is widely tuneable with interactions along the BCS-BEC crossover and is suppressed on the BEC side. We propose as an experimental signature of the odd-even effect the damping rate of quadrupole oscillations, which is anomalously enhanced due to the presence of long-lived odd-parity modes. Our findings suggest that the dynamics of two-dimensional Fermi gases is richer than previously thought and should include additional long-lived modes.