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

Recent experiments have pointed to 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 nonepitaxial Bi/Ni bilayers, superconductivity arises due to the formation of $\mathrm{Ni}{\mathrm{Bi}}_{3}$, which has been reported to host coexisting ferromagnetic and superconducting orders at the surface. We perform high-resolution surface magneto-optic Kerr effect measurements using a Sagnac interferometer on single-crystal $\mathrm{Ni}{\mathrm{Bi}}_{3}$ and find no sign of any spontaneous Kerr signal except for contributions from trapped vortices. This strongly indicates the absence of TRSB in $\mathrm{Ni}{\mathrm{Bi}}_{3}$, whether due to TRSB in the superconducting state or any coexisting ferromagnetism, and we conclude that the superconductivity found in nonepitaxial Bi/Ni is distinctively different from that in epitaxial Bi/Ni.