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arXiv · 2609.27079

Spectroscopic signatures of persistent exciton condensation in a bulk magnetic topological insulator

Paulina Majchrzak·Chakradhar Sahoo·Manuel Tuniz·Wibke Bronsch·Denny Puntel·Federico Cilento·Xing-Chen Pan·Jakob Kjærulff Svaneborg·Yong P. Chen·Søren Ulstrup
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Abstract

Exciton condensates are long-sought correlated quantum states arising from macroscopic coherence of bound electron-hole pairs. Although equilibrium and transient excitonic states have been reported in several material platforms, direct evidence for a light-induced exciton condensate state has been challenging to achieve as an intrinsic property of a bulk quantum material. Here, we use time- and angle-resolved photoemission spectroscopy to investigate long-lived photoexcited carriers in the intrinsic magnetic topological insulator MnBi$_2$Te$_4$ with the chemical potential tuned to the topological surface state by Sb substitution. Following optical excitation, we observe the delayed emergence of a transient state whose formation coincides with depopulation of the bulk conduction band and whose lifetime extends to the microsecond timescale. The quasiparticle dispersion exhibits a pronounced flattening and develops a Mexican-hat-like profile. These spectral signatures are consistent with the formation of a metastable excitonic condensate state. Our results establish magnetic topological insulators as a promising platform for investigating long-lived photoinduced many-body states and their interplay with topology and magnetism.

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Paulina Majchrzak, Chakradhar Sahoo, Manuel Tuniz, Wibke Bronsch, Denny Puntel, Federico Cilento, Xing-Chen Pan, Jakob Kjærulff Svaneborg, Yong P. Chen, Søren Ulstrup. 2026-09-22. Spectroscopic signatures of persistent exciton condensation in a bulk magnetic topological insulator. https://arxiv.org/abs/2609.27079

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