Pair Fluctuation Effects on Quasiparticle Transport in Fermi Systems

TL;DR

This paper develops a theoretical framework to understand how pair fluctuations influence quasiparticle transport near a Cooper instability, with applications to superconductors, nuclear matter, and liquid helium-3.

Contribution

It formulates corrections to the Landau-Boltzmann equation using Keldysh field theory, providing a unified approach for various Fermi systems near pairing transitions.

Findings

Quantitative agreement with experiments on zero sound attenuation in liquid helium-3.

Theoretical predictions for the effects of Zeeman fields on pairing fluctuations.

Applicability to both conventional and unconventional superconductors.

Abstract

The leading corrections to Fermi liquid theory for non-equilibrium quasiparticle transport near a Cooper instability arise from the virtual emission and absorption of incipient Cooper pairs. We formulate the corrections to the Landau-Boltzmann transport equation starting from Keldysh's field theory for non-equilibrium, strongly interacting Fermions. The theory is applicable to quasiparticle transport in conventional and unconventional superconductors, dense nuclear matter and the low temperature phases of liquid $^3$He. Validation of the theory is provided by our analysis, and quantitative agreement between theory and experiment, of the excess attenuation of zero sound in liquid $^3$He near the superfluid transition. We propose an additional experimental test of the theory based on the effects of a Zeeman field on the spectrum of pairing fluctuations for the Cooper instability in spin-triplet superfluids.