Fermi arc reconstruction at the interface of twisted Weyl semimetals

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.