Point Node Gap Structure of the Spin-Triplet Superconductor UTe2

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Date/Time:Thursday, 11 Feb 2021 from 4:10 pm to 5:00 pm
Channel:Condensed Matter Physics
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Tristin Metz, University of Maryland

Low-temperature electrical and thermal transport, magnetic penetration depth, and heat capacity measurements were performed on single crystals of the actinide superconductor UTe2(Tc =1.6K) to determine the structure of the superconducting energy gap. Heat transport measurements performed with currents directed along both crystallographic a- and b-axes reveal a vanishingly small residual fermionic component of the thermal conductivity. The magnetic field dependence of the residual term follows a quasi-linear increase consistent with the presence of nodal quasiparticles, rising rapidly toward the a-axis upper critical field where the Wiedemann-Franz (WF) law is recovered. Together with a quadratic temperature dependence of the magnetic penetration depth up to T/Tc = 0.3, these measurements provide evidence for an unconventional spin-triplet superconducting order parameter with point nodes positioned along the crystallographic a-axis. Millikelvin specific heat measurements reveal an upturn below 300 mK that is well described by a divergent quantum-critical contribution to the density of states (DOS). Modeling this contribution with a T^(1/3) power law allows restoration of the full entropy balance in the superconducting state and reveals a perfect T^3 power law for the electronic DOS below Tc which is consistent with the point nodal gap structure determined by thermal conductivity and penetration depth measurements.