Ballistic magnon transport and phonon scattering in the antiferromagnet Nd$_2$CuO$_4$

TL;DR

This study investigates heat transport in Nd$_2$CuO$_4$, revealing ballistic magnon conduction below 0.5 K and detailed phonon-magnon scattering mechanisms through thermal conductivity measurements.

Contribution

It demonstrates the use of a spin-flop transition to distinguish magnon and phonon heat contributions and characterizes magnon velocity and scattering rates at ultra-low temperatures.

Findings

Magnons exhibit ballistic transport below 0.5 K with T^3 thermal conductivity.

Magnon-phonon scattering rate increases as T^3.

Phonon scattering by magnons peaks at twice the magnon frequency.

Abstract

The thermal conductivity of the antiferromagnet Nd$_2$CuO$_4$ was measured down to 50 mK. Using the spin-flop transition to switch on and off the acoustic Nd magnons, we can reliably separate the magnon and phonon contributions to heat transport. We find that magnons travel ballistically below 0.5 K, with a thermal conductivity growing as $T^3$, from which we extract their velocity. We show that the rate of scattering of acoustic magnons by phonons grows as $T^3$, and the scattering of phonons by magnons peaks at twice the average Nd magnon frequency.