Anisotropic two-gap superconductivity and the absence of a Pauli paramagnetic limit in single-crystalline LaO0.5F0.5BiS2

Abstract

Ambient-pressure-grown LaO0.5F0.5BiS2 with a superconducting transition temperature Tc∼3 K possesses a highly anisotropic normal state. By a series of electrical resistivity measurements with a magnetic-field direction varying between the crystalline c axis and the ab plane, we present datasets displaying the temperature dependence of the out-of-plane upper critical field Hc2⊥(T), the in-plane upper critical field Hc2∥(T), as well as the angular dependence of Hc2 at fixed temperatures for ambient-pressure-grown LaO0.5F0.5BiS2 single crystals. The anisotropy of the superconductivity, Hc2∥/Hc2⊥, reaches ∼16 on approaching 0 K, but it decreases significantly near Tc. A pronounced upward curvature of Hc2∥(T) is observed near Tc, which we analyze using a two-gap model. Moreover, Hc2∥(0) is found to exceed the Pauli paramagnetic limit, which can be understood by considering the strong spin-orbit coupling associated with Bi as well as the breaking of the local inversion symmetry at the electronically active BiS2 bilayers. Hence, LaO0.5F0.5BiS2 with a centrosymmetric lattice structure is a unique platform to explore the physics associated with local parity violation in the bulk crystal.

Source-reported materials — not catalogue approval

Similar papers