Higher-nodal collective modes in a resonantly interacting Fermi gas

TL;DR

This paper experimentally investigates higher-nodal axial collective modes in a resonantly interacting Fermi gas, revealing their temperature dependence and validating theoretical models, thus advancing understanding of superfluid dynamics.

Contribution

It provides the first detailed experimental analysis of higher-nodal modes in a unitary Fermi gas and compares results with Landau's two-fluid theory, confirming its validity.

Findings

Higher-nodal modes can be efficiently excited and analyzed.

Mode frequencies depend on temperature across the superfluid transition.

Results agree well with theoretical predictions based on Landau's two-fluid theory.

Abstract

We report on experimental investigations of longitudinal collective oscillations in a highly elongated, harmonically trapped two-component Fermi gas with resonantly tuned s-wave interactions ('unitary Fermi gas'). We focus on higher-nodal axial modes, which in contrast to the elementary modes have received little attention so far. We show how these modes can be efficiently excited using a resonant local excitation scheme and sensitively analyzed by a Fourier transformation of the detected time evolution of the axial density profile. We study the temperature dependence of the mode frequencies across the superfluid phase transition. The behavior is qualitatively different from the elementary modes, where the mode frequencies are independent of the temperature as long as the gas stays in the hydrodynamic regime. Our results are compared to theoretical predictions based on Landau's two-fluid theory and available experimental knowledge of the equation of state. The comparison shows excellent agreement and thus both represents a sensitive test for the validity of the theoretical approach and provides an independent test of the equation of state. The present results obtained on modes of first-sound character represent benchmarks for the observation of second-sound propagation and corresponding oscillation modes.