New phase diagram for (U,Th)Be13: A muon-spin-resonance andHC1study

Zero-field muon-spin-resonance and lower-critical-field data are presented for a wide range of Th concentrations in ${\mathrm{U}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Th}}_{\mathit{x}}$ ${\mathrm{Be}}_{13}$, spanning the region where both a superconducting and a second, lower-temperature phase transition are observed. Overall T-x phase boundaries are assigned and discussed according to the nature of the lower phase transition. Arguments for associating the lower phase with a possible magnetic (time-reversal–violating) superconducting state are given.