njie Yu

Absence of Magnetic Thermal Conductivity in the Quantum Spin-Liquid Candidate YbMgGaO4

We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO_{4}, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (C_{m}∼T^{0.74}). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields H≥6  T, the exponential T dependence of C_{m} and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state. The absence of magnetic thermal conductivity at the zero field in this QSL candidate puts a strong constraint on the theories of its ground state.

Fully gapped superconducting state in Au2Pb: A natural candidate for topological superconductor

We measured the ultra-low-temperature specific heat and thermal conductivity of the Au2Pb single crystal, a possible three-dimensional Dirac semimetal with a superconducting transition temperature . The electronic specific heat can be fitted by a two-band s-wave model, which gives the gap amplitudes Δ1(0)/k B T c = 1.41 and Δ2(0)/k B T c = 5.25. From the thermal conductivity measurements, a negligible residual linear term in zero field and a slow field dependence of at low field are obtained. These results suggest that Au2Pb has a fully gapped superconducting state in the bulk, which is a necessary condition for topological superconductors if Au2Pb is indeed one.