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Title: Direct measurement of a non-Hermitian topological invariant in a hybrid light-matter system
Authors: Su, Rui
Estrecho, Eliezer
Biegańska, Dąbrówka
Huang, Yuqing
Wurdack, Matthias
Pieczarka, Maciej
Truscott, Andrew G.
Liew, Timothy Chi Hin
Ostrovskaya, Elena A.
Xiong, Qihua
Keywords: Science::Physics::Optics and light
Issue Date: 2021
Source: Su, R., Estrecho, E., Biegańska, D., Huang, Y., Wurdack, M., Pieczarka, M., Truscott, A. G., Liew, T. C. H., Ostrovskaya, E. A. & Xiong, Q. (2021). Direct measurement of a non-Hermitian topological invariant in a hybrid light-matter system. Science Advances, 7(45), eabj8905-.
Project: MOE2018-T3-1-002
Journal: Science Advances
Abstract: Topology is central to understanding and engineering materials that display robust physical phenomena immune to imperfections. Different topological phases of matter are characterized by topological invariants. In energy-conserving (Hermitian) systems, these invariants are determined by the winding of eigenstates in momentum space. In non-Hermitian systems, a topological invariant is predicted to emerge from the winding of the complex eigenenergies. Here, we directly measure the non-Hermitian topological invariant arising from exceptional points in the momentum-resolved spectrum of exciton polaritons. These are hybrid light-matter quasiparticles formed by photons strongly coupled to electron-hole pairs (excitons) in a halide perovskite semiconductor at room temperature. We experimentally map out both the real (energy) and imaginary (linewidth) parts of the spectrum near the exceptional points and extract the novel topological invariant—fractional spectral winding. Our work represents an essential step toward realization of non-Hermitian topological phases in a condensed matter system.
ISSN: 2375-2548
DOI: 10.1126/sciadv.abj8905
Schools: School of Physical and Mathematical Sciences 
Rights: © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
Fulltext Permission: open
Fulltext Availability: With Fulltext
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