Fermi arc reconstruction at the interface of twisted Weyl semimetals

TL;DR

This paper investigates how twisting and tunnel-coupling between two Weyl semimetals alter their surface Fermi arcs, revealing conditions where arcs become loops and impact optical conductivity under magnetic fields.

Contribution

It provides a detailed analysis of Fermi arc evolution at the interface of twisted Weyl semimetals, highlighting conditions for arc-to-loop transitions and their optical signatures.

Findings

Fermi arcs can become Fermi loops without endpoints.

Connectivity changes in Fermi surfaces affect optical conductivity.

Surface states decay exponentially in certain regimes.

Abstract

Three-dimensional Weyl semimetals have pairs of topologically protected Weyl nodes, whose projections onto the surface Brillouin zone are the end points of zero energy surface states called Fermi arcs. At the endpoints of the Fermi arcs, surface states extend into and are hybridized with the bulk. Here, we consider a two-dimensional junction of two identical Weyl semimetals whose surfaces are twisted with respect to each other and tunnel-coupled. Confining ourselves to commensurate angles (such that a larger unit cell preserves a reduced translation symmetry at the interface) enables us to analyze arbitrary strengths of the tunnel-coupling. We study the evolution of the Fermi arcs at the interface, in detail, as a function of the twisting angle and the strength of the tunnel-coupling. We show unambiguously that in certain parameter regimes, all surface states decay exponentially into the bulk, and the Fermi arcs become Fermi loops without endpoints. We study the evolution of the `Fermi surfaces' of these surface states as the tunnel-coupling strengths vary. We show that changes in the connectivity of the Fermi arcs/loops have interesting signatures in the optical conductivity in the presence of a magnetic field perpendicular to the surface.