Year: 2026
Type: preprint
Abstract: Excitons are conventionally expected to destabilize at high photoexcitation densities, as screening weakens the electron-hole attraction. Recent studies, however, challenge this paradigm, suggesting that excitons generated by strong optical pumping can remain stable even beyond the onset of population inversion. Here, using time- and angle-resolved photoelectron spectroscopy on 2D hybrid perovskites, we provide direct evidence for such a high-density excitonic state, characterized by a distinctive Mexican-hat dispersion. Remarkably, this excitonic band reconstruction endures for orders of magnitude longer than the optical coherence time, revealing a population-sustained electronic structure that survives well into the incoherent regime. The excitonic resonance also persists far beyond optical saturation, at densities where exciton wavefunctions strongly overlap. Our findings reveal a long-lived, high-density quantum fluid of excitons with characteristics reminiscent of a BCS condensate, an electronic structure markedly different from that of the dilute limit.
Source: arXiv (Cornell University)
Institutions: Centre National de la Recherche Scientifique, École Polytechnique, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Laboratoire de physique des Solides, Laboratoire des Solides Irradiés, SR University, University of Rome Tor Vergata, Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata, Synchrotron SOLEIL, Lund University, NanoLund, Technical University of Denmark, Institut Polytechnique de Paris
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1399589686, G6224526311
OpenAlex ID: W7223679613