Manipulating the nematic director by magnetic fields in the spin-triplet superconducting state of CuxBi2Se3

Electronic nematicity, a consequence of rotational symmetry breaking, is an emergent phenomenon in various new materials. In order to fully utilize the functions of these materials, ability of tuning them through a knob, the nematic director, is desired. Here we report a successful manipulation of the nematic director, the vector order parameter (d vector), in the spin-triplet superconducting state of CuxBi2Se3 by magnetic fields. At H = 0.5 T, the ac susceptibility related to the upper critical field shows a twofold symmetry in the basal plane. At H = 1.5 T, however, the susceptibility shows a sixfold symmetry, which has never been reported before in any superconductor. These results indicate that the d vector initially pinned to a certain direction is unlocked by a threshold field to respect the trigonal crystal symmetry. We further reveal that the superconducting gap in different crystals converges to px symmetry at high fields, although it differs at low fields.