2020/04/30 by Benjamin J. Wieder, Kuan-Sen Lin, Barry Bradlyn · 1 citation
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1103/physrevresearch.2.042010
published as Phys. Rev. Research 2, 042010 (2020) · v3: approximately published verison. v2: Fixed typos, clarified discussion of applicability to real material systems, and added extensions to time-reversal invariant models. 4.5 + 11pgs + references, 4+3 figures. v1: 4.5 + 7pgs + references, 4+1 figures
arxiv created 2020/10/16 · arxiv updated 2020/10/21
In recent theoretical and experimental investigations, researchers have linked the low-energy field theory of a Weyl semimetal gapped with a charge-density wave (CDW) to high-energy theories with axion electrodynamics. However, it remains an open question whether a lattice regularization of the dynamical Weyl-CDW is in fact a single-particle axion insulator (AXI). In this Letter, we use analytic and numerical methods to study both lattice-commensurate and incommensurate minimal (magnetic) Weyl-CDW phases in the mean-field state. We observe that, as previously predicted from field theory, the two inversion- (I-) symmetric Weyl-CDWs with ϕ= 0,π differ by a topological axion angle δθϕ=π. However, we crucially discover that neither of the minimal Weyl-CDW phases at ϕ=0,π is individually an AXI; they are instead quantum anomalous Hall (QAH) and "obstructed" QAH insulators that differ by a fractional translation in the modulated cell, analogous to the two phases of the Su-Schrieffer-Heeger model of polyacetylene. Using symmetry indicators of band topology and non-abelian Berry phase, we demonstrate that our results generalize to multi-band systems with only two Weyl fermions, establishing that minimal Weyl-CDWs unavoidably carry nontrivial Chern numbers that prevent the observation of a static magnetoelectric response. We discuss the experimental implications of our findings, and provide models and analysis generalizing our results to nonmagnetic Weyl- and Dirac-CDWs.