Topological surface states host superconductivity induced by the bulk condensate in YRuB$_2$

TL;DR

This paper demonstrates that YRuB₂ hosts topological surface states that become superconducting due to the bulk condensate, providing a single-material platform for topological superconductivity with potential applications.

Contribution

It provides experimental evidence of topological surface states in YRuB₂ that acquire superconductivity, confirming theoretical predictions and highlighting a single-stoichiometric material for TSC research.

Findings

Detection of a bulk superconducting gap of ~1 meV.

Observation of a smaller superconducting gap (~0.5 meV) on topological surface states.

Confirmation that topological surface states in YRuB₂ are induced to superconduct via proximity to the bulk condensate.

Abstract

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 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 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 YRuB$_2$ due to the proximity of the bulk superconducting condensate. Thus, in agreement with the past theoretical predictions, we present YRuB$_2$ as a unique system that hosts superconducting topological surface states.