High-pressure study of the basal-plane anisotropy of the upper critical field of the topological superconductor SrxBi2Se3

We report a high-pressure transport study of the upper-critical field B-c2(T) of the topological superconductor Sr0.15Bi2Se3 (T-c = 3.0 K). B-c2(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 p(c) similar to 3.5 GPa, the pronounced two-fold basal-plane anisotropy B-c2(a)/B-c2(a*) = 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 similar to 5 at the highest pressure (2.2 GPa). The data reveal that the unconventional superconducting state with broken rotational symmetry is robust under pressure.