New SubmissionTwo-dimensional superconductivity with unconventional magnetotransports in PtPb₄ single crystals: a new nonsymmorphic symmetry-protected topological superconductor

This study presents a new nonsymmorphic symmetry-protected topological phase, as well as a two-dimensional surface topological superconductivity on PtPb₄ surface. The bulk superconductivity of PtPb₄ exhibited characteristic of a conventional moderately-coupled Bardeen–Cooper–Schrieffer non-ideal type-II superconductor. Nevertheless, the superconductivity investigated via electrical transport exhibited anisotropic properties of 2D nature, verified through a Berezinsky-Kosterlitz-Thouless transition and 2D-like vortex dynamics in mixed-state transports. The obtained activation energy U(H), critical current density J_c(T, H), and scaling of pinning forces for F_p(H) for PtPb₄ showed a relatively weak vortex pinning in PtPb₄, accompanied by a crossover of the flux-line lattice from elastic relaxation to shear deformation. In the normal state, PtPb₄ revealed nontrivial quantum interference transports with a crossover from weak-antilocalization- to weak-localization-dominated transverse magnetoresistance in the low-field region, demonstrating the presence of topological surface states on PtPb₄. The observed 2D superconductivity can be attributed to the dispersion of topological Dirac-like surface band in PtPb₄. Our findings provide robust support for the emergence of a new nonsymmorphic symmetry-protected topological phase on the PtPb₄ surface. Thus, PtPb₄ is one of the few reported nonsymmorphic symmetry-protected topological superconductors.