Excitons are particle-like entities that form when electrons bind to electron vacancies called holes. A long-standing goal in condensed-matter physics is the unambiguous creation of a collective quantum state of excitons, known as a Bose-Einstein condensate, in a two-dimensional (2D) material; such a state could be used to study quantum effects and might find applications in quantum technology. A crucial step toward this goal is the observation that an ensemble of excitons in a 2D-material system can emit light in a spatially coherent manner. This feat has now been achieved by Alexander Holleitner at the Technical University of Munich and his colleagues [1].
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