While the possibility of topological superconductivity (TSC) in hybrid heterostructures involving topologically nontrivial band structure and superconductors has been proposed, the realization of TSC in a single stoichiometric material is most desired for fundamental experimental investigation of TSC and its device applications. Bulk measurements on ${\mathrm{YRuB}}_2$ detect a single superconducting gap of $\sim 1$ meV. This is supported by our electronic structure calculations, which also reveal the existence of topological surface states in the system. We performed surface-sensitive Andreev reflection spectroscopy on ${\mathrm{YRuB}}_2$ and detected the bulk superconducting gap as well as another superconducting gap of $\sim 0.5$ meV. From our analysis of electronic structure, we show that the smaller gap is formed in the topological surface states in ${\mathrm{YRuB}}_2$ due to the proximity of the bulk superconducting condensate. Thus, in agreement with the past theoretical predictions, we present ${\mathrm{YRuB}}_2$ as a unique system that hosts superconducting topological surface states.

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• Andreev reflection
• First-principles calculations
• Proximity effect
• Superconductivity
• Topological superconductors