Low-Temperature Heat Transport in the Low-Dimensional Quantum Magnet NiCl_{2}-4SC(NH_{2})_{2}

TL;DR

This study investigates low-temperature thermal conductivity in a spin-1 chain quantum magnet, revealing anomalies at critical fields and demonstrating magnons' dual role as scatterers and heat carriers in the magnon BEC state.

Contribution

It provides the first detailed measurement of thermal conductivity in NiCl_{2}-4SC(NH_{2})_{2} across the magnon BEC transition, highlighting magnons' changing role in heat transport.

Findings

Strong anomalies in thermal conductivity at critical fields.

Magnons switch from phonon scatterers to heat carriers at low temperatures.

Large thermal conductivity observed in the magnon BEC state.

Abstract

We report a study of the low-temperature thermal conductivity of NiCl_{2}-4SC(NH_{2})_{2}, which is a spin-1 chain system exhibiting the magnon Bose-Einstein condensation (BEC) in magnetic field. It is found that the low-T thermal conductivity along the spin-chain direction shows strong anomalies at the lower and upper critical fields of the magnon BEC state. In this state, magnons act mainly as phonon scatterers at relatively high temperature, but change their role to heat carriers upon temperature approaching zero. The result demonstrates a large thermal conductivity in the magnon BEC state and points to a direct analog between the magnon BEC and the conventional one.