Weyl nodal surfaces

TL;DR

This paper explores Weyl nodal surfaces in 3D fermionic systems, demonstrating their topological robustness, symmetry protection, and associated surface states through theoretical models.

Contribution

It introduces the concept of Weyl nodal surfaces, analyzes their topological stability, and investigates their surface states and doubling phenomena in four-band models.

Findings

Weyl nodal surfaces are topologically robust under small Hamiltonian perturbations.

Surface states associated with nodal surfaces are identified and characterized.

Nodal surface doubling phenomena are analyzed in the context of symmetry protections.

Abstract

We consider three-dimensional fermionic band theories that exhibit Weyl nodal surfaces defined as two-band degeneracies that form closed surfaces in the Brillouin zone. We demonstrate that topology ensures robustness of these objects under small perturbations of a Hamiltonian. This topological robustness is illustrated in several four-band models that exhibit nodal surfaces protected by unitary or anti-unitary symmetries. Surface states and Nielsen-Ninomiya doubling of nodal surfaces are also investigated.