This study presents a new nonsymmorphic symmetry-protected topological phase, as well as a two-dimensional (2D) surface topological superconductivity on ${\mathrm{PtPb}}_4$ surface. The bulk superconductivity of ${\mathrm{PtPb}}_4$ exhibited characteristic of a conventional moderately-coupled Bardeen–Cooper–Schrieffer nonideal 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 $J_{\mathrm{c}}(T,H)$, and scaling of pinning forces for $F_{\mathrm{p}}\left(H\right)$ for ${\mathrm{PtPb}}_4$ showed a relatively weak vortex pinning in ${\mathrm{PtPb}}_4$, accompanied by a crossover of the flux-line lattice from elastic relaxation to shear deformation. In the normal state, ${\mathrm{PtPb}}_4$ revealed nontrivial quantum interference transports with a crossover from weak-antilocalization- to weak-localization-dominated transverse magnetoresistance (TMR) in the low-field region, demonstrating the presence of topological surface states on ${\mathrm{PtPb}}_4$. Besides, the violation of Kohler's rule with a power-law exponent value of 1.4 also revealed a nontrivial MR characteristic of ${\mathrm{PtPb}}_4$. The pronounced exotic TMR characteristic confirmed that ${\mathrm{PtPb}}_4$ indeed hosts topological surface states, driven by a new nonsymmorphic symmetry-protected topological phase. All results are summarized in a constructed phase diagram of ${\mathrm{PtPb}}_4$ in the H-T plane, displaying different regimes of transport. The observed 2D superconductivity, as well as nontrivial quantum-interference transports, can be attributed to the dispersion of topological Dirac-like surface band in ${\mathrm{PtPb}}_4$. Our findings provide robust support for the emergence of a new nonsymmorphic symmetry-protected topological phase on the ${\mathrm{PtPb}}_4$ surface. Thus, ${\mathrm{PtPb}}_4$ is one of the few reported nonsymmorphic symmetry-protected topological superconductors, paving the way for the development of superconducting quantum computation.

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• Topological superconductors
• Type-II superconductors
• Magnetization measurements
• Resistivity measurements
• Specific heat measurements