Absence of spontaneous time-reversal symmetry breaking and ferromagnetism in superconducting NiBi3 single crystal

Abstract: Recent experiments have pointed to a chiral p-wave-like superconductivity in epitaxial Bi/Ni bilayers that are spontaneously time-reversal symmetry breaking (TRSB), making it a promising platform for exploring physics useful for topologically protected quantum computing. Quite intriguingly, evidence has emerged that in non-epitaxial Bi/Ni bilayers, superconductivity arises due to the formation of NiBi3, which has been reported to host coexisting ferromagnetic and superconducting orders at the surface. We perform high resolution surface magneto-optic Kerr effect (SMOKE) measurements using a Sagnac interferometer on single crystal NiBi3 and find no sign of any spontaneous Kerr signal except for contributions from trapped vortices. This strongly indicates the absence of TRSB in NiBi3, whether due to TRSB in the superconducting state or any coexisting ferromagnetism, and we conclude that the superconductivity found in non-epitaxial Bi/Ni is distinctively different from that in epitaxial Bi/Ni.