Probing quantum spin liquids in equilibrium using the inverse spin Hall effect

TL;DR

This paper proposes an experimental method using a bilayer of a strongly spin-orbit coupled metal and a quantum magnet to detect quantum spin liquids by analyzing voltage noise spectra, enabling identification of different spin liquid states.

Contribution

It introduces a novel equilibrium bilayer technique to probe quantum spin liquids through voltage noise spectrum analysis, with specific predictions for various models.

Findings

Predicted frequency characteristics for three quantum spin liquid models.

Ability to extract spinon gaps in the kagome lattice model.

Detection of the two-flux gap in the Kitaev model.

Abstract

We propose an experimental method utilizing a strongly spin-orbit coupled metal to quantum magnet bilayer that will probe quantum magnets lacking long range magnetic order, e.g., quantum spin liquids, via examination of the voltage noise spectrum in the metal layer. The bilayer is held in thermal and chemical equilibrium, and spin fluctuations arising across the single interface are converted into voltage fluctuations in the metal as a result of the inverse spin Hall effect. We elucidate the theoretical workings of the proposed bilayer system, and provide precise predictions for the frequency characteristics of the enhancement to the ac electrical resistance measured in the metal layer for three candidate quantum spin liquid models. Application to the Heisenberg spin-$1/2$ kagom{\'e} lattice model should allow for the extraction of any spinon gap present. A quantum spin liquid consisting of fermionic spinons coupled to a $U(1)$ gauge field should cause subdominant $\W^{4/3}$ scaling of the resistance of the coupled metal. Finally, if the magnet is well-captured by the Kitaev model in the gapless spin liquid phase, then the proposed bilayer can extract the two-flux gap which arises in spite of the gapless spectrum of the fermions. We therefore show that spectral analysis of the ac resistance in the metal in a single interface, equilibrium bilayer can test the relevance of a quantum spin liquid model to a given candidate material.