QuMat seminar
2025-02-05, 16:00 – BBG 7.12Heat-carrying sound in liquid ³He and in metallic Fermi liquidsSpeaker: Kamran Behnia – CNRS & ESPCI, Paris, France Host: Lars Fritz |
Abstract
Landau’s theory of Fermi liquids explains why electrons in metals can be considered as a degenerate Fermi gas despite the strong repulsive interaction. According to this picture, a strongly interacting system of fermions can be mapped to a system consisting of “quasi-particles” with a residual weak interaction.
Landau’s theory was inspired by ³He, an exceptional case of zero-temperature liquid of interacting fermions. However, and contrary to what is generally assumed, thermal conductivity of ³He below its degeneracy temperature [1], is not only set by Landau’s quasi-particles. There is another contribution with a distinct temperature dependence [2], caused by a collective mode [3] in the hydrodynamic limit. This expression for heat-carrying sound is a quantum version of the Bridgman equation for thermal conductivity of classical liquids [4]. A collective mode may also be relevant to transport in strongly correlated Fermi liquids whose resistivity deviates from a quadratic behavior well below the Fermi degeneracy temperature.
[2] K. Behnia & K. Trachenko, Nature Commun. 15, 1771 (2024).
[3] F. Albergamo et al., Phys. Rev. Lett. 99, 205301 (2007).
[4] P. W. Bridgman, P. W. Proc. Am. Acad. Arts Sci. 59, 141–169 (1923).