Thermodynamic signatures of a fractionalized Fermi liquid

TL;DR

This paper investigates the thermodynamic signatures of a fractionalized Fermi liquid state in heavy-fermion metals, highlighting how spinons influence thermal conductivity and spin susceptibility, especially near quantum critical points.

Contribution

It introduces a detailed analysis of thermal and magnetic properties of a spin liquid state with gapless fermionic excitations in both 2D and 3D, providing new theoretical insights.

Findings

Thermal transport is dominated by spinons in clean samples within certain temperature ranges.

A characteristic maximum in the Wiedemann-Franz ratio indicates fractionalization effects.

Spin susceptibility shows a logarithmic enhancement over Fermi liquid behavior in three dimensions.

Abstract

Several heavy-fermion metals display a quantum phase transition from an antiferromagnetic metal to a heavy Fermi liquid. In some materials, however, recent experiments seem to find that the heavy Fermi liquid phase can be directly tuned into a non-Fermi liquid phase without apparent magnetic order. We analyze a candidate state for this scenario where the local moment system forms a spin liquid with gapless fermionic excitations. We discuss the thermal conductivity and spin susceptibility of this fractionalized state both in two and, in particular, three spatial dimensions for different temperature regimes. We derive a variational functional for the thermal conductivity and solve it with a variational ansatz dictated by Keldysh formalism. In sufficiently clean samples and for an appropriate temperature window, we find that thermal transport is dominated by the spinon contribution which can be detected by a characteristic maximum in the Wiedemann-Franz ratio. For the spin susceptibility, the conduction electron Pauli paramagnetism is much smaller than the spinon contribution whose temperature dependence in three dimensions is logarithmically enhanced as compared to the Fermi liquid result.