Low-temperature heat transport of spin-gapped quantum magnets

TL;DR

This review discusses low-temperature heat transport in spin-gapped quantum magnets, highlighting how magnetic excitations influence thermal conductivity and phase transitions in various low-dimensional quantum systems.

Contribution

It provides a comprehensive overview of experimental and theoretical findings on magnetic heat transport in spin-gapped systems, emphasizing recent advances and controversies.

Findings

Large ballistic thermal conductivity in S=1/2 ladders

Controversial results in Haldane chain systems

Magnetic excitations can both carry heat and scatter phonons

Abstract

This article reviews low-temperature heat transport studies of spin-gapped quantum magnets in the last few decades. Quantum magnets with small spins and low dimensionality exhibit a variety of novel phenomena. Among them, some systems are char-acteristic of having quantum-mechanism spin gap in their magnetic excitation spectra, including spin-Peierls systems, S = 1 Haldane chains, S = 1/2 spin ladders, and spin dimmers. In some particular spin-gapped systems, the XY-type antiferromagnetic state induced by magnetic field that closes the spin gap can be described as a magnon Bose-Einstein condensation (BEC). Heat transport is effective in probing the magnetic excitations and magnetic phase transitions, and has been extensively studied for the spin-gapped systems. A large and ballistic spin thermal conductivity was observed in the two-leg Heisenberg S = 1/2 ladder compounds. The characteristic of magnetic thermal transport of the Haldane chain systems is quite controversial on both the theoretical and experimental results. For the spin-Peierls system, the spin excitations can also act as heat carriers. In spin-dimer compounds, the magnetic excitations mainly play a role of scattering phonons. The magnetic excitations in the magnon BEC systems displayed dual roles, carrying heat or scattering phonons, in different materials.