Fully gapped superconductivity with preserved time-reversal symmetry in NiBi3 single crystals

作者：Shang, T.^*; Meng, J.; Zhu, X. Y.; Zhang, H.; Yu, B. C.; Zhen, X.; Wang, Y. H.; Xu, Y.; Zhan, Q. F.; Gawryluk, D. J.; Shiroka, T.

来源：Physical Review B, 2023, 107(17): 174513.

DOI：10.1103/PhysRevB.107.174513

• PENETRATION-DEPTH
• FERROMAGNETISM
• NEUTRON

We report a study of NiBi3 single crystals by means of electrical-resistivity, magnetization, and muon-spin rotation and relaxation (mu SR) measurements. As a single crystal, NiBi3 adopts a needlelike shape and exhibits bulk superconductivity with T-c approximate to 4.1 K. By applying magnetic fields parallel and perpendicular to the b axis of NiBi3, we establish that its lower and upper critical fields as well as the magnetic penetration depths show slightly different values, suggesting a weakly anisotropic superconductivity. In both cases, the zero-temperature upper critical fields are much smaller than the Pauli-limit value, indicating that the superconducting state is constrained by the orbital pair breaking. The temperature evolution of the superfluid density, obtained from transverse-field mu SR, reveals a fully gapped superconductivity in NiBi3, with a shared superconducting gap Lambda(0) = 2.1k(B)T(c) and magnetic penetration depths lambda(0) = 223 and 210 nm for H parallel to b and H perpendicular to b, respectively. The lack of spontaneous fields below T-c indicates that time-reversal symmetry is preserved in NiBi3. The absence of a fast muon-spin relaxation and/or precession in the zero-field mu SR spectra definitely rules out any type of magnetic ordering in NiBi3 single crystals. Overall, our investigation suggests that NiBi3 behaves as a conventional s-type superconductor.