High pressure study of the basal plane anisotropy of the upper critical field of the topological superconductor Sr x Bi 2 Se 3
We report a high pressure transport study of the upper critical field Bc2(T) of the topological superconductor Sr0.15Bi2Se3 (Tc=3.0 K) Bc2(T) was measured for magnetic fields directed along two orthogonal directions, a and a* in the trigonal basal plane. While superconductivity is rapidly suppressed at the critical pressure pc~3.5 GPa, the pronounced two fold basal plane anisotropy Bac2/Ba*c2=3.2 at T=0.3 K, recently reported at ambient pressure [Pan et al. Sci. Rep. 6 28632 (2016) is reinforced and attains a value of ~5 at the highest pressure (2.2 GPa) The data reveal that the unconventional superconducting state with broken rotational symmetry is robust under pressure.