title: Excitonic phases from Weyl semimetals.
abstract: Systems with strong spin-orbit coupling, which competes with other interactions and energy scales, offer a fertile playground to explore new correlated phases of matter. Weyl semimetals are an example where the phenomenon leads to a low-energy effective theory in terms of massless linearly dispersing fermions in three dimensions. In the absence of interactions chirality is a conserved quantum number, protecting the semimetallic physics against perturbations that are translationally invariant. In this Letter we show that the interplay between interaction and topology yields a novel chiral excitonic insulator. The state is characterized by a complex vectorial order parameter leading to a gapping out of the Weyl nodes. A striking feature is that it is ferromagnetic, with the phase of the order parameter determining the direction of the induced magnetic moment.
authors.affiliation: Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
authors.forename: Huazhou
authors.initials: H
authors.lastname: Wei
authors.forename: Sung-Po
authors.initials: SP
authors.lastname: Chao
authors.forename: Vivek
authors.initials: V
authors.lastname: Aji