Metal-insulator Transition in Weyl Semimetal Thin Films

In this talk we demonstrate metal-insulator transition in Weyl semimetal thin films using model Hamiltonians, and introduce special cases in which a quadratic crossing remains even in single-layer limit. The band structure of Weyl semimetals is distinguished by pairs of Dirac points in the 3D Brillouin zone which are sink and source of the Berry curvature. These Weyl nodes act like magnetic monopoles with opposite charges in momentum space. In a slab configuration, this non-trivial topology leads to topological surface states that form unique Fermi arcs connecting two Weyl nodes. Here we show that as the thickness of the slab is reduced, the Fermi arcs shrink with the two magnetic monopoles moving toward each other, distinguishing the top of the Fermi arc as the most stable metallic point on the surface. In the absence of symmetries to protect the metallic crossing at the top of the arc, the metallic surface states disappear at a critical thickness. In special cases in which the metallic state at the top of the Fermi arc is protected by symmetries in the 2D plane, the pair of Fermi arcs on opposite surfaces reduces to a quadratic crossing in the thin film. Finally, we use density functional theory to explore the manifestations of this Fermi arc evolution in real material systems.