Low field magnetic response of the non-centrosymmetric superconductor YPtBi

The low-field magnetic response of the non-centrosymmetric superconductor YPtBi (Tc=0.77K) is investigated. Ac-susceptibility and dc-magnetization measurements provide solid evidence for bulk superconductivity with a volume fraction of ~70%. The lower critical field is surprisingly small: Bc1 =0.008mT (T→0T→0). Muon spin rotation experiments in a transverse magnetic field of 0.01 T show a weak increase of the Gaussian damping rate σTFσTF below Tc, which yields a London penetration depth λ=1.6±0.2μm. The zero-field Kubo-Toyabe relaxation rate σKTσKT equals 0.129±0.004μs−1 and does not show a significant change below Tc. This puts an upper bound of 0.04 mT on the spontaneous magnetic field associated with a possible odd-parity component in the superconducting order parameter.