Pressure-induced surface superconductivity in the noncentrosymmetric superconductor PbTaSe2: Pressure-dependent point-contact Andreev spectroscopy

A notable characteristic of PbTaSe2, a prototypical noncentrosymmetric superconductor (NCS), is that its superconductivity can be modulated through a structural transition under hydrostatic pressure [Kaluarachchi et al. Phys. Rev. B 95, 224508 (2017)]. Here we report on a combined pressure -sensitive point -contact Andreev reflection (PCAR) spectroscopy with bulk resistance measurements on PbTaSe2, to elucidate the nature of the surface and bulk superconductivity and their evolution with hydrostatic pressure. It is found that in a high-pressure region the superconducting gap opening temperature TcA is significantly lower than the bulk resistive transition temperature TcR, revealing a clear experimental signature of surface -bulk separation associated with enhanced antisymmetric spin -orbit coupling (ASOC). The PCAR spectra, reflecting the superconducting surface state, are analyzed with two-dimensional Blonder-Tinkham-Klapwijk theory, yielding an isotropic s -wave full BCS gap in the strong -coupling regime. These results suggest the coexistence of full gap s -wave superconductivity and topological surface states in PbTaSe2, indicating that this NSC superconductor with significantly enhanced ASOC may offer a solid platform to investigate the topological aspect in the superconducting condensate.