Exotic surface states in hybrid structures of topological insulators and Weyl semimetals

TL;DR

This paper explores the theoretical possibility of hybrid surface states formed at the boundary between topological insulators and Weyl semimetals, revealing new Dirac nodes and spin-polarized dispersions.

Contribution

It introduces a coupled model of TIs and WSMs, analytically deriving hybrid surface states and their dispersion relations under different coupling symmetries.

Findings

Two Dirac nodes can emerge from hybridization with spin-symmetric coupling.

The dispersion relation can be gapped and spin-polarized with spin-asymmetric coupling.

Proposes experimental setups like strained HgTe and heterostructures for realization.

Abstract

Topological insulators (TIs) and Weyl semimetals (WSMs) are two realizations of topological matter usually appearing separately in nature. However, they are directly related to each other via a topological phase transition. In this paper, we investigate the question whether these two topological phases can exist together at the same time, with a combined, hybrid surface state at the joint boundaries. We analyze effective models of a 3D TI and an inversion symmetric WSM and couple them in a way that certain symmetries, like inversion, are preserved. A tunnel coupling approach enables us to obtain the hybrid surface state Hamiltonian analytically. This offers the possibility of a detailed study of its dispersion relation depending on the investigated couplings. For spin-symmetric coupling, we find that two Dirac nodes can emerge out of the combination of a single Dirac node and a Fermi arc. For spin-asymmetric coupling, the dispersion relation is gapped and the former Dirac node gets spin-polarized. We propose different experimental realization of the hybrid system, including compressively strained HgTe as well as heterostructures of TI and WSM materials.