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.