Collective excitations in a fermion-fermion mixture with different Fermi surfaces

TL;DR

This paper investigates collective excitations in a fermion-fermion mixture with different Fermi surfaces, revealing how superfluid phases and phase mode velocities relate to Fermi velocities, offering potential detection methods.

Contribution

It introduces a detailed analysis of collective modes in fermion mixtures with different Fermi surfaces, highlighting the velocity relations and superfluid phase detection.

Findings

Zero-sound velocity exceeds the largest Fermi velocity.

Superfluid phase emerges below a critical temperature with attractive interactions.

Phase mode velocity is proportional to the geometric mean of the two Fermi velocities.

Abstract

In this paper, collective excitations in a homogeneous fermion-fermion mixture with different Fermi surfaces are studied. In the Fermi liquid phase, the zero-sound velocity is found to be larger than the largest Fermi velocity. With attractive interactions, the superfluid phase appears below a critical temperature, and the phase mode is the low-energy collective excitation. The velocity of the phase mode is proportional to the geometric mean of the two Fermi velocities. The difference between the two velocities may serve as a tool to detect the superfluid phase.