Field-Angle-Resolved Specific Heat in Co-based Kitaev quantum spin liquid candidate

Layered honeycomb magnets, such as Kitaev quantum spin liquid (KSL) candidates, are known for hosting Majorana quasiparticles whose excitations are highly sensitive to the direction of an applied magnetic field [1]. In materials like α-RuCl₃, specific heat experiments in high-field phases have demonstrated a clear angular dependence of low-energy excitations, consistent with predictions from the Kitaev model, and providing bulk evidence supporting the KSL state [2,3]. Here we present low-temperature measurements of specific heat C(T) for another KSL candidate Na₂Co₂TeO₆ (NCTO) and BaCo₂(AsO₄)₂ (BCAO) under field rotation within the honeycomb plane. In NCTO, above the critical field of antiferromagnetic order, the field-angle dependence of C/T exhibits minima along the bond directions, contrasting with the maxima observed in the KSL state of α-RuCl₃. Our analysis indicates nodeless, fully-gapped excitations, which are inconsistent with the angle-dependent Majorana excitations with gapless nodes predicted by the Kitaev model [4]. On the other hand, BCAO exhibits gapless-like excitations and we would like to discuss the difference between these two materials in the presentation.