Quantum muon diffusion and the preservation of time-reversal symmetry in the superconducting state of type-I rhenium

Elemental rhenium exhibiting type-II superconductivity has been previously\nreported to break time-reversal symmetry in the superconducting state. We have\ninvestigated an arc-melted sample of rhenium exhibiting type-I\nsuperconductivity. Low temperature zero-field muon-spin relaxation measurements\nindicate that time-reversal symmetry is preserved in the superconducting state.\nMuon diffusion is observed, which is due to quantum mechanical tunneling\nbetween interstitial sites. The normal state behavior is characterized by the\nconduction electrons screening the muons and thermal broadening, and is typical\nfor a metal. Energy asymmetries between muon trapping sites and the\nsuperconducting energy gap also characterize the superconducting state\nbehavior.\n