Observation of the diffusive Nambu-Goldstone mode of a non-equilibrium phase transition

Ferdinand Claude; Maxime J. Jacquet; Michiel Wouters; Elisabeth Giacobino; Quentin Glorieux; Iacopo Carusotto; Alberto Bramati

arXiv · 2310.11903

Observation of the diffusive Nambu-Goldstone mode of a non-equilibrium phase transition

Ferdinand Claude·Maxime J. Jacquet·Michiel Wouters·Elisabeth Giacobino·Quentin Glorieux·Iacopo Carusotto·Alberto Bramati

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Abstract

Second-order phase transitions are governed by spontaneous symmetry breaking, which yield collective excitations with a gapless spectrum called Nambu-Goldstone (NG) modes. While NG modes in conservative systems are propagating excitations, non-equilibrium phase transitions have been predicted to feature a diffusive NG mode. We present the first experimental evidence of a diffusive NG mode in a non-equilibrium Bose-Einstein condensate of microcavity polaritons. The NG mode is observed as a spectral narrowing in the spectroscopic response of the condensate. Additionally, explicitly breaking the symmetry causes the opening of a gap in the spectrum and the disappearance of the NG mode. Our observations confirm the diffusive dynamics of the NG mode of non-equilibrium phase transitions and establish a promising framework to investigate fundamental questions in statistical mechanics.

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Ferdinand Claude, Maxime J. Jacquet, Michiel Wouters, Elisabeth Giacobino, Quentin Glorieux, Iacopo Carusotto, Alberto Bramati. 2023-10-18. Observation of the diffusive Nambu-Goldstone mode of a non-equilibrium phase transition. https://arxiv.org/abs/2310.11903

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