Ultralow-temperature heat transport in the quantum spin liquid candidate Ca10Cr7O28 with bilayer kagome lattice

TL;DR

This study investigates ultralow-temperature heat transport in Ca10Cr7O28, a candidate quantum spin liquid, revealing no gapless excitations and suggesting a gapped or localized spinon state, thus constraining theoretical models.

Contribution

The paper provides experimental thermal conductivity data on Ca10Cr7O28, showing the absence of gapless itinerant fermionic excitations and indicating a gapped or localized spinon state.

Findings

No residual linear term in thermal conductivity at zero temperature.

Thermal conductivity shows a dip around 6 T magnetic field.

Estimated spin gap of approximately 0.27 K.

Abstract

Recently, a novel material with bilayer kagome lattice Ca$_{10}$Cr$_7$O$_{28}$ was proposed to be a gapless quantum spin liquid, due to the lack of long-range magnetic order and the observation of broad diffuse excitations. Here, we present the ultralow-temperature thermal conductivity measurements on single crystals of Ca$_{10}$Cr$_7$O$_{28}$ to detect its low-lying magnetic excitations. At finite temperatures, with increasing the magnetic fields, the thermal conductivity exhibits a clear dip around 6 T, which may correspond to a crossover in the magnetic ground state. At the zero-temperature limit, no residual linear term is found at any fields, indicating the absence of gapless itinerant fermionic excitations. Therefore, if the spinons do exist, they are either localized or gapped. In the gapped case, the fitting of our data gives a small gap $\Delta \sim$ 0.27(2) K. These results put strong constraints on the theoretical description of the ground state in this quantum spin liquid candidate.