Magnetic field induced Quantum Criticalities in the triangular antiferromagnet KYbSe₂

Quantum spin liquid (QSL) is a state of matter characterized by fractionalized quasiparticle excitations, quantum entanglement, and a lack of long-range magnetic order. QSL so far has evaded a definitive experimental observation. There have been several Yb³⁺ based materials (S = ½) suggested as QSL candidates, but thus far, their studies have not provided unambiguous proof of a QSL. Here we investigate the Yb³⁺ delafossite material KYbSe₂, a promising QSL candidate, via specific heat and magnetocaloric measurements of a single crystal of KYbSe₂ down to 30 mK. The heat capacity C shows an anomaly at T_N = 0.29 K in zero field, consistent with magnetic ordering demonstrated at this temperature by neutron scattering studies. Analysis of the low-temperature specific heat at 0 T indicates the presence of a T-linear component of C/T in the proximate QSL region above T_N suggested by neutron scattering experiments at low temperature. When magnetic field is applied along the a-axis, both T-linear and T-logarithmic behavior at higher temperature are suppressed, and we observe multiple magnetically ordered phases in the H-T phase diagram.