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 ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$ by magnetic fields. At $H=0.5\mathrm{T}$, the ac susceptibility related to the upper critical field shows a twofold symmetry in the basal plane. At $H=1.5\mathrm{T}$, however, the susceptibility shows a sixfold symmetry, which has never been reported before in any superconductor. These results indicate that the $\mathbf{d}$ 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 $p_x$ symmetry at high fields, although it differs at low fields.

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• Superconductivity
• Unconventional superconductors
• Nuclear magnetic resonance
• Susceptibility measurements