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The interplay of superconductivity with nontrivial topological phases exhibit the fascinating topological superconductivity, which has attracted widespan attention from observing quasiparticle like Majorana fermions to its application in fault-tolerant quantum computation$^{1,2}$. It is proposed that the topological superconductivity can be realized in compounds having topological surface states and superconductivity$^3$. Only a few superconducting materials with nontrivial topological states have been discovered, and their superconducting ground state/pairing mechanism can not be adequately understood. Therefore, searching and studying the superconducting ground state of materials having nontrivial topological states is vital.
Here, we present the evidence of time-reversal symmetry breaking (TRSB) in the nonsymmorphic type-I superconductor YbSb$_2$, having a distorted Sb square net crystal structure similar to the other topological system ZrSiS$^{4,5}$. The microscopic muon spin relaxation and rotation investigation confirm the fully gapped type-I superconductivity with broken time-reversal symmetry in its superconducting ground state. This indicates that the nonsymmorphic RSb$_2$ superconductors are an interesting class of materials that exhibit unconventional superconductivity with fascinating properties and warrant great potential for future studies.
References:
1. X. L. Qi et al., Rev. Mod. Phys. 83, 1057 (2011).
2. M. Sato et al., Rep. Prog. Phys. 80, 076501 (2017).
3. L. Fu et al., Phys. Rev. Lett. 100, 096407 (2008).
4. R. Wang et al., Inorg. Chem. 5, 1468 (1966).
5. S. Klemenz et al., Ann. Rev. Mat. Res. 49, 185 (2019).
