# Type-I and type-II topological nodal superconductors with $s$-wave interaction

## TL;DR

This paper introduces a minimal model for topological nodal superconductors using only s-wave interactions, revealing novel phases with potential experimental realizations and robustness against disorder.

## Contribution

It proposes a new minimal model that achieves topological nodal phases with s-wave pairing, involving anisotropic spin-orbit couplings and topological classifications.

## Key findings

- Supports various nodal phases characterized by winding number or Pfaffian.
- Nodal points can be described by type-I or type-II Dirac equations.
- Nodal phases are robust against weak disorder.

## Abstract

Topological nodal superconductors are generally realized based on unconventional pairings. In this work, we propose a minimal model to realize these topological nodal phases with only $s$-wave interaction. In our model the linear and quadratic spin-orbit couplings along the two directions break the isotropy in momentum space and introduce effective unconventional pairings on the Fermi surface. This model may support different nodal superconducting phases characterized by either winding number in BDI class or Pfaffian in D class at the particle-hole invariant axes. In the vicinity of the nodal points the effective Hamiltonian can be described by either type-I or type-II Dirac equation; and the crossover between these two nodal points can be driven by external Zeeman fields. We show that these nodal phases are robust against weak disorders, thus are possible to be realized in experiments with real materials. The smoking-gun evidences to verify these phases based on scanning tunneling spectroscopy are also briefly discussed.