Characterizing the Superconducting State of Cu_xBi₂Se₃ Through Muon-Spin Relaxation/Rotation

The discovery of topological superconductors has been a major objective in the field since they were first predicted theoretically. The doped topological insulator Cu_xBi₂Se₃ is a promising candidate for topological superconductivity, but there is much conflicting evidence on the subject. Identifying the superconducting symmetry of the material is paramount in determining whether it has a topologically nontrivial ground state. Muon spin relaxation/rotation (SR) experiments provide a heretofore unexplored method of probing the superconducting state of Cu_xBi₂Se₃. Here, we present SR data collected on a single-crystal sample of Cu_0.3Bi₂Se₃. Measurements conducted in zero-field conditions demonstrate that time reversal symmetry is preserved in the superconducting state, while transverse-field measurements reveal superfluid density behavior that is consistent with p-wave pairing. Such a scenario could support topological superconductivity in Cu_xBi₂Se₃. However, a more conventional s-wave pairing scenario also provides a reasonable fit to the data, making an unambiguous conclusion difficult. Nevertheless, these results represent a valuable addition to the body of experimental data available for Cu_xBi₂Se₃.