Time Reversal Symmetry Breaking in noncentrosymmetric superconductor Re6Ti

We have investigated the superconducting state of the noncentrosymmetric superconductor Re6Ti (Tc = 6.0 K) using muon-spin rotation/relaxation (muSR) technique. The zero-field muon experiment shows the presence of spontaneous magnetic fields in the superconducting state, indicating time-reversal symmetry breaking (TRSB). However, the low-temperature transverse field muon measurements suggest nodeless s-wave superconductivity. The time reversal symmetry breaking further confirmed in the stoichiometric composition Re24Ti5. These results indicate that the pairing symmetry is not affected by spin-orbital coupling Re6X family of compounds. Altogether these studies suggest unconventional nature (TRSB) of superconductivity is intrinsic to Re6X family of compounds and paves the way for further studies of this family of materials.