Paramagnetic Meissner effect in topological superconductor candidate Sr_xBi₂Se₃

Single crystals of superconducting Sr_xBi₂Se₃ with the actual Sr content up to x = 0.14 have been grown. The highest T_c = 3.12 K has been observed in x = 0.048 sample in electrical transport measurment and it decreases with the increase of actual Sr content. The highest superconducting volume fraction is close to 100% determined from magnetic susceptibility measurement at 1.75 K. An unexpected paramagnetic Messner effect (PME) has been observed in all measured Sr_xBi₂Se₃ samples at lower magnetic fields. We attribute this PME to imhomogeneous microstructure of Sr_xBi₂Se₃, which was supported by transmission electron microscope (TEM) analysis. In addition, resistive transitions under magnetic fields point to an unconventional temperature dependence of the upper critical field B_c2.