# Thermal conductivity of the quantum spin liquid candidate EtMe3Sb[Pd(dmit)2]2: No evidence of mobile gapless excitations

## TL;DR

This study measures the thermal conductivity of a quantum spin liquid candidate, finding no evidence of mobile gapless excitations, thus suggesting localized low-energy excitations and challenging previous reports of gapless behavior.

## Contribution

The paper provides the first low-temperature thermal conductivity measurements of EtMe3Sb[Pd(dmit)2]2, showing absence of mobile gapless excitations and clarifying its spin-liquid nature.

## Key findings

- Residual linear thermal conductivity $ o$ localized excitations
- No evidence of mobile gapless excitations in the material
- Heat conduction dominated by phonons with strong spin-phonon scattering

## Abstract

The thermal conductivity $\kappa$ of the quasi-2D organic spin-liquid candidate EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ (dmit-131) was measured at low temperatures, down to 0.07 K. We observe a vanishingly small residual linear term $\kappa_0/T$, in $\kappa/T$ vs $T$ as $T \to 0$. This shows that the low-energy excitations responsible for the sizeable residual linear term $\gamma$ in the specific heat $C$, seen in $C/T$ vs $T$ as $T \to 0,$ are localized. We conclude that there are no mobile gapless excitations in this spin liquid candidate, in contrast with a prior study of dmit-131 that reported a large $\kappa_0/T$ value [Yamashita et al., Science 328, 1246 (2010)]. Our study shows that dmit-131 is in fact similar to $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, another quasi-2D organic spin-liquid candidate where a vanishingly small $\kappa_0/T$ and a sizeable $\gamma$ are seen. We attribute heat conduction in these organic insulators without magnetic order to phonons undergoing strong spin-phonon scattering, as observed in several other spin-liquid materials.