Heat transport of cuprate-based low-dimensional quantum magnets with strong exchange coupling

TL;DR

This review discusses how heat transport measurements in cuprate-based low-dimensional quantum magnets reveal insights into exotic magnetic quasiparticles, showing efficient and sometimes ballistic spin-heat conduction consistent with theoretical models.

Contribution

It provides a comprehensive overview of experimental findings on magnetic heat transport in cuprate quantum magnets, highlighting the role of various quasiparticles and their transport properties.

Findings

Magnetic heat transport can be highly efficient and sometimes ballistic.

Experimental evidence supports the existence of fractionalized spinons.

Transport properties vary across different low-dimensional quantum magnetic models.

Abstract

Transport properties provide important access to a solid's quasiparticles, such as quasiparticle density, mobility, and scattering. The transport of heat can be particularly revealing because, in principle, all types of excitations in a solid may contribute. Heat transport is well understood for phonons and electrons, but relatively little is known about heat transported by magnetic excitations. However, during the last about two decades, the magnetic heat transport attracted increasing attention after the discovery of large and unusual signatures of it in low-dimensional quantum magnetic cuprate materials. Today it constitutes an important probe to otherwise often elusive, topological quasiparticles in a broader class of quantum magnets. This review summarizes the experimental foundation of this research, i.e. the state of the art for the magnetic heat transport in the mentioned cuprate materials which host prototypical low-dimensional antiferromagnetic $S=1/2$ Heisenberg models. These comprise, in particular, the two-dimensional square lattice, and one-dimensional spin chain and two-leg ladder spin models. It is shown, how studying the heat transport provides direct access to the thermal occupation and the scattering of the already quite exotic quasiparticles of these models which range from spin-1 spin wave and triplon excitations to fractionalized spin-1/2 spinons. Remarkable transport properties of these quasiparticles have been revealed: the spin-heat transport often is highly efficient and in some cases even ballistic, in agreement with theoretical predictions.