Muon spin rotation study of the topological superconductor SrxBi2Se3

We report transverse-field (TF) muon spin rotation experiments on single crystals of the topological superconductor SrxBi2Se3 with nominal concentrations x = 0.15 and 0.18 (T-c similar to 3 K). The TF spectra (B = 10 mT), measured after cooling to below Tc in field, did not show any additional damping of the muon precession signal due to the flux line lattice within the experimental uncertainty. This puts a lower bound on the magnetic penetration depth lambda >= 2.3 mu m. However, when we induce disorder in the vortex lattice by changing the magnetic field below T-c, a sizable damping rate is obtained for T -> 0. The data provide microscopic evidence for a superconducting volume fraction of similar to 70% in the x = 0.18 crystal and thus bulk superconductivity.