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Quantum spin liquids (QSLs) are a proposed state of matter characterized by fractionalized quasiparticle excitations, quantum entanglement and a lack of long range magnetic order. QSLs have so far evaded definitive experimental observation. There has been significant study of Yb³⁺ based materials as QSL candidates due to the Yb³⁺ S = ½ state, but thus far these studies have not provided an unambiguous proof of a QSL. Here we investigate the Yb³⁺ delafossite material KYbSe₂, which is a promising QSL candidate.

We present low temperature (T ≥ 30 mK) measurements of the heat capacity of single crystal KYbSe₂, in which we observe signatures of a magnetic ordering transition at 300 mK, consistent with neutron scattering studies of KYbSe₂. We discuss the effect of applying an in-plane (Hǁab) magnetic field on the transition and on the temperature dependence of the heat capacity. We use the nuclear Schottky anomaly due to static Yb electron spins to track the evolution of the magnetically ordered state as a function of magnetic field.