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DY: Fachverband Dynamik und Statistische Physik
DY 32: Poster: Active Matter, Soft Matter, Fluids
DY 32.5: Poster
Mittwoch, 20. März 2024, 15:00–18:00, Poster C
PT Symmetry and Non-Hermitian Band Topology — •Kang Yang1, Zhi Li2, Lukas König3, Lukas Rødland3, Marcus Stålhammar4, and Emil Bergholtz3 — 1Freie Universität Berlin, Berlin, Germany — 2Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada — 3Stockholm University, Stockholm, Sweden — 4Nordita, Stockholm, Sweden
Non-Hermitian matrices are ubiquitous in the description of nature ranging from classical dissipative systems, including optical, electrical, and mechanical metamaterials, to scattering of waves and open quantum many-body systems. Multiple non-Hermitian bands exhibit intriguing exceptional points, spectral braids and crossings. In this work we develop a topological description based on non-Hermitian band gaps and separation gaps. We provide a unified classification of both gapped and nodal systems in the presence of physically relevant parity-time (PT) and pseudo-Hermitian symmetries using homotopy theory. This uncovers new stable topology stemming from both eigenspectra and wavefunctions, and remarkably also implies distinct fragile topological phases. In particular, we reveal different Abelian and non-Abelian phases in PT-symmetric systems, described by frame and braid topology. The corresponding invariants are robust to symmetry-preserving perturbations that do not induce (exceptional) degeneracy, and they also predict the deformation rules of nodal phases. We further demonstrate that spontaneous PT symmetry breaking is captured by Chern-Euler and Chern-Stiefel-Whitney descriptions, a fingerprint of unprecedented non-Hermitian topology overlooked in previous study.
Keywords: PT symmetry; Non-Hermitian systems; Band topology; Photonics and metamaterials