期刊
SCIENCE ADVANCES
卷 7, 期 45, 页码 -出版社
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/sciadv.abj8905
关键词
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资金
- National Natural Science Foundation of China [12020101003]
- State Key Laboratory of Low-Dimensional Quantum Physics
- Tsinghua University
- Singapore Ministry of Education via AcRF Tier 3 Programme Geometrical Quantum Materials [MOE2018-T3-1-002]
- AcRF Tier 2 grants [MOE2017-T2-1-001, MOE2018-T2-02-068, MOE2019-T2-1-004]
- Australian Research Council (ARC) through the Centre of Excellence [CE170100039]
- Foundation for Polish Science in the START programme
The text discusses the importance of topology in understanding and designing robust materials, as well as measuring the topological invariants in both Hermitian and non-Hermitian systems. It presents the measurement of a non-Hermitian topological invariant in the momentum-resolved spectrum of exciton polaritons, highlighting the potential for realizing non-Hermitian topological phases in condensed matter systems.
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.
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