Types of topological surface states in nodal noncentrosymmetric superconductors

TL;DR

This paper explores the diverse topological surface states in nodal noncentrosymmetric superconductors, revealing new types of states influenced by lattice symmetries and their experimental signatures.

Contribution

It introduces novel topological features of surface states arising from inversion symmetries and provides a comprehensive theoretical framework for their protection and detection.

Findings

Identification of surface arcs connecting nodal rings

Majorana states at time-reversal-invariant momenta

Topological invariants for different surface states

Abstract

Nodal noncentrosymmetric superconductors have topologically nontrivial properties manifested by protected zero-energy surface states. Specifically, it was recently found that zero-energy surface flat bands of topological origin appear at their surface. We show that the presence of certain inversion-type lattice symmetries can give rise to additional topological features of the gap nodes, resulting in surface states forming one-dimensional arcs connecting the projections of two nodal rings. In addition, we demonstrate that Majorana surface states can appear at time-reversal-invariant momenta of the surface Brillouin zone, even when the system is not fully gapped in the bulk. Within a continuum theory we derive the topological invariants that protect these different types of zero-energy surface states. We independently derive general conditions for the existence of zero-energy surface bound states using the complementary quasiclassical scattering theory, explicitly taking into account the effects of spin-orbit splitting of the bands. We compute surface bound-state spectra for various crystal point-group symmetries and orbital-angular-momentum pairing states. Finally, we examine the signatures of the arc surface states and of the zero-energy surface flat bands in tunneling-conductance spectra and discuss how topological phase transitions in noncentrosymmetric superconductors could be observed in experiments.