# Disorder and Zeeman coupling induced gap-filling states in the nodeless chiral superconducting Bi/Ni bilayer system

## TL;DR

This paper investigates how impurities and Zeeman coupling induce gap-filling states in a fully gapped chiral superconductor in Bi/Ni bilayers, potentially explaining observed zero-bias anomalies.

## Contribution

It demonstrates that both impurities and Zeeman fields can generate in-gap states in a helical d-wave superconductor, offering a new understanding of experimental tunneling anomalies.

## Key findings

- Impurities create states within the superconducting gap.
- Zeeman coupling can produce Bogoliubov Fermi surfaces.
- Results explain zero-bias anomalies in tunneling measurements.

## Abstract

Motivated by the recently discovered time-reversal symmetry-breaking superconductivity in epitaxial Bi/Ni bilayer system with transition temperature $T_c\approx 4.2$K and the observation of zero-bias anomaly in tunneling measurements, we show that gap-filling states can appear in the fully gapped $d_{xy}\pm id_{x^2-y^2}$ superconducting states. We consider a model of helical electron states with d-wave pairing. In particular, we show that both magnetic and non-magnetic impurities can create states within the superconducting gap. Alternatively, we also 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. Our findings may explain the origin of zero-bias anomaly observed in the point-contact tunneling measurements.