Nodal-line semimetals from Weyl superlattices

TL;DR

This paper demonstrates how Weyl superlattices with engineered periodic potentials can host stable nodal-line semimetal phases, highlighting the role of reflection and charge-conjugation symmetries without requiring small spin-orbit coupling.

Contribution

It introduces a model showing the emergence of nodal-line semimetals in Weyl systems through superlattice engineering, emphasizing symmetry protections beyond lattice symmetries.

Findings

Nodal lines can be stabilized by reflection and combined symmetries.

Surface states include both exponentially localized drumhead states and weakly localized states.

The model does not require small spin-orbit coupling for nodal line formation.

Abstract

The existence and topological classification of lower-dimensional Fermi surfaces is often tied to the crystal symmetries of the underlying lattice systems. Artificially engineered lattices, such as heterostructures and other superlattices, provide promising avenues to realize desired crystal symmetries that protect lower-dimensional Fermi surface, such as nodal lines. In this work, we investigate a Weyl semimetal subjected to spatially periodic onsite potential, giving rise to several phases, including a nodal-line semimetal phase. In contrast to proposals that purely focus on lattice symmetries, the emergence of the nodal line in this setup does not require small spin-orbit coupling, but rather relies on its presence. We show that the stability of the nodal line is understood from reflection symmetry and a combination of a fractional lattice translation and charge-conjugation symmetry. Depending on the choice of parameters, this model exhibits drumhead surface states that are exponentially localized at the surface, or weakly localized surface states that decay into the bulk at all energies.