Effects of momentum dissipation on thermoelectricity in strongly correlated Fermi liquids

Despite their high power factors, strongly correlated Fermi liquids with large Fermi surfaces, in particular heavy fermions, have very low dimensionless figures of merit, ZT. This is because the Wiedemann-Franz (WF) law can be applied to such systems as well as to ordinary metals. On the other hand, some Fermi liquids with small Fermi surfaces, such as an antiferromagnetic metal, CeRhIn5, and a Weyl semimetal, WP2, significantly violate the WF law, which works in the direction of increasing the ZT. Here we theoretically study the thermoelectric properties of a spin-1/2 strongly correlated Fermi liquid with a single Fermi surface, based on the Kubo-Luttinger formula in linear response theory. For a large Fermi surface with about one carrier per site, the Umklapp processes in electron-electron scattering cause strong momentum dissipation, and our theory is in good accord with experiments on heavy-fermion compounds. When the number of carriers per site is reduced to about 0.1, however, the momentum dissipation is suppressed and a significant violation of the WF law occurs, where not only a large power factor but also a ZT greater than 1 is found. This finding provides important guidance for the design of high-performance thermoelectric materials in strongly correlated metals.