Existence of topological degeneracies and half vortices in layered anisotropic continuous media
Phys. Rev. B 114, 125305 – Published 10 August, 2026
DOI: https://doi.org/10.1103/1p8r-lxy8
Abstract
Topological degeneracies (TD) and half vortices with nontrivial charges have been widely studied in various metastructures, which mainly relies on the symmetry breaking of structures. Here, by resorting to material anisotropy rather than geometric asymmetry, we designed a layered anisotropic dielectric system and found that rotating the optical axis (OA) of one layer not only breaks the symmetry of such layered system but also brings TD and circularly polarized states (C points) that are absent in single-layer anisotropic system. In detail, two bulk Fermi arcs with pairs of exceptional points can evolve into a pair of Dirac point, and the two Dirac points will eventually annihilate as the rotates along the polar direction. During this process, C points will merge and undergo the charge exchange with degenerate points. When rotating the OA in the direction of azimuth angle, a quadratic degeneracy can be split into a pair of Dirac points, or vice versa. Our work reveals the modulating effects of anisotropy on TD and singularities, paving the way for exploring more topological physics in naturally anisotropic materials without specific structural design.
