Gap-filling states induced by disorder and Zeeman coupling in the nodeless chiral superconducting Bi/Ni bilayer system

摘要

Motivated by the recently discovered time-reversal symmetry-breaking superconductivity in the epitaxial Bi/Ni bilayer system with transition temperature T-c approximate to 4.2 K and the observation of a zero-bias anomaly in a background of gap-filling states in tunneling measurements, we show that gap-filling states can appear in the fully gapped d(xy) +/- id(x2)(-y2) superconducting states. We consider a model of helical electron states with d-wave pairing. In particular, we show that both magnetic and nonmagnetic impurities can create states within the superconducting gap. Alternatively, we show that the coupling of the electron spins to the in-plane Zeeman field provided by nickel can also create gap-filling states by producing Bogoliubov Fermi surfaces.