Dynamic Many-Body Theory. II. Dynamics of Strongly Correlated Fermi Fluids

TL;DR

This paper develops a systematic many-body theory for strongly correlated Fermi fluids, extending bosonic models to predict dynamic responses and excitations, with applications to helium-3 and electronic systems.

Contribution

It generalizes existing bosonic theories to fermionic systems, providing quantitative predictions for dynamic structure functions in strongly interacting Fermi fluids.

Findings

Lowered zero sound mode in helium-3

Broadening of collective modes due to particle-hole coupling

Observation of a double-plasmon excitation in electronic systems

Abstract

We develop a systematic theory of multi-particle excitations in strongly interacting Fermi systems. Our work is the generalization of the time-honored work by Jackson, Feenberg, and Campbell for bosons, that provides, in its most advanced implementation, quantitative predictions for the dynamic structure function in the whole experimentally accessible energy/momentum regime. Our view is that the same physical effects -- namely fluctuations of the wave function at an atomic length scale -- are responsible for the correct energetics of the excitations in both Bose and Fermi fluids. Besides a comprehensive derivation of the fermion version of the theory and discussion of the approximations made, we present results for homogeneous He-3 and electrons in three dimensions. We find indeed a significant lowering of the zero sound mode in He-3 and a broadening of the collective mode due to the coupling to particle-hole excitations in good agreement with experiments. The most visible effect in electronic systems is the appearance of a ``double-plasmon'' excitation.