The coexistence of non-trivial band structure and superconductivity can host a novel phase known as topological superconductivity [1]. A typical host of non-trivial band structures is the topological semimetal, a class of gapless electronic phases that exhibit topologically stable band crossings [2]. The possibility of topological superconductivity in a type-I superconductor opens the door to exotic physics. The topological semimetal SnAs shows superconductivity below 3.6 K, but there is ambiguity in the nature of superconductivity. Some reports claim type-I superconductivity in SnAs [3,4], but recent studies contradict it [5]. We have resolved this enigma using a thorough microscopic analysis of the superconducting ground state.

In this work, we report the muon spin rotation/relaxation (μSR) study of the possible topological superconductor SnAs [6]. The zero-field (ZF) μSR data reveal that this system is a time-reversal-invariant superconductor. The systematic transverse-field (TF) μSR measurements reveal type-I superconductivity and the intermediate state in the superconducting phase diagram of SnAs. Moreover, ab initio calculations of band structure and phonons were performed, which correlate with the basic experimental characterization. Our study opens a platform for understanding the underlying physics behind the origin of topological superconductivity in type-I superconductors.

[1] M. Sato and Y. Ando, Rep. Prog. Phys. 80, 076501 (2017).

[2] A. Burkov, Nat. Mater. 15, 1145 (2016).

[3] P. I. Bezotosnyi, et al., Phys. Rev. B 100, 184514 (2019).

[4] Y. Wang, et al., Chem. Mater. 26, 7209 (2014).

[5] M. M. Sharma, et al., Solid State Commun. 340, 114531 (2021).

[6] S. Srivastava, et al., arXiv:2512.17282 (2025).