[PAST EVENT] Physcis Colloquium - Hyunsoo Kim
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Hyunsoo Kim, University of Maryland-College Park, Title of talk: Anomalous electrical transport and unconventional superconductivity in Half-Heusler YPtBi
Abstract: The Half-Heusler RTBi compound (R=rare earth, T=transition metal) is a promising platform to study interactions between topological ordered phase and various symmetry-breaking ordered ground states. YPtBi is a prototypical topological semimetal with j=3/2 conduction fermions driven by strong spin-orbit coupling. It undergoes a superconducting phase transition at T = 0.8 K surprisingly only with a carrier density as low as 1018 cm-3. This challenges conventional Eliashberg formalism of superconductivity based on the electron-phonon interaction. Naturally, the normal state and superconducting state properties in the topological semimetal YPtBi are of great interest. In this talk, I will present recently discovered anomalous transport and superconducting properties in YPtBi. In normal state, the angle-dependent magnetoresistance breaks the rotational symmetry of the underlying cubic crystal structure, which can be understood by two-channel conduction model with at least one channel having a lower rotational symmetry than the crystal symmetry. At high magnetic fields, Shubnikov-de Haas quantum oscillations are readily visible. However, the amplitude of the quantum oscillation abruptly vanishes along certain crystallographic orientations. I will explain the unusual quantum oscillations in YPtBi within a semiclassical picture with the effective spin g-factor of conduction fermions affected by strong spin-orbit coupling. Finally, I will talk about unconventional nodal superconductivity with j=3/2 fermions in cubic YPtBi, which can be explained by unprecedented higher spin Cooper pairing beyond spin-triplet.