Gapless Spin Liquids: Stability and Possible Experimental Relevance

TL;DR

This paper discusses the stability and experimental relevance of gapless spin liquids, proposing specific Z4 and Z2 spin liquid states with pseudo-Fermi surfaces as promising candidates for explaining experimental observations in certain organic compounds.

Contribution

It introduces a theoretical framework identifying Z4 and Z2 spin liquids with pseudo-Fermi surfaces as key candidates, and presents a solvable model on the triangular lattice supporting a Z2 spin liquid ground state.

Findings

Identification of Z4 spin liquids with pseudo-Fermi surfaces as promising candidates.

Proposal of a Z2 spin liquid with broken symmetries as a stable phase.

Presentation of a solvable model supporting a Z2 spin liquid ground state.

Abstract

For certain crystalline systems, most notably the organic compound EtMe3Sb[Pd(dmit)2]2, experimental evidence has accumulated of an insulating state with a high density of gapless neutral excitations that produce Fermi-liquid-like power laws in thermodynamic quantities and thermal transport. This has been taken as evidence of a fractionalized spin liquid state. In this paper, we argue that if the experiments are taken at face value, the most promising spin liquid candidates are a Z4 spin liquid with a pseudo-Fermi surface and no broken symmetries, or a Z2 spin-liquid with a pseudo-Fermi surface and at least one of the following spontaneously broken: (a) time-reversal and inversion, (b) translation, or (c) certain point-group symmetries. We present a solvable model on the triangular lattice with an (a) type Z2 spin liquid groundstate.