Thermal Conductivity Measurements of a Quantum Spin Liquid Candidate

In the vast majority of materials that host strongly interacting localised moments, long-range magnetic order will be established at some finite temperature. However, if this long-range order is suppressed by - for example - geometric frustration, a theorised quantum spin liquid (QSL) state might instead emerge. This is a phase of matter characterised by the long-range quantum entanglement of localised moments, which can in some cases give rise to fractionalised, dispersive excitations. In the material NaYbSe₂, pseudospin-1/2 moments are localised at the Yb sites, and so lie geometrically frustrated within effective two-dimensional triangular layers. Previous studies have demonstrated that, at mK temperatures, the material exhibits no long range order, a large finite heat capacity and a two-dimensional spectrum of gapless excitations. These are all hallmarks of a QSL, and the material might therefore be a physical realisation of the QSL state. In this work, we have measured the thermal conductivity of NaYbSe₂ at temperatures outside the QSL phase. Our results have interesting implications for the material's QSL candidacy.