Observation of scale invariance and universality in two-dimensional Bose gases

Chen Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin

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Abstract

The collective behaviour of a many-body system near a continuous phase transition is insensitive to the details of its microscopic physics; for example, thermodynamic observables follow generalized scaling laws near the phase transition. The Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two-dimensional Bose gases presents a particularly interesting case because the marginal dimensionality and intrinsic scaling symmetry result in a broad fluctuation regime and an extended range of universal scaling behaviour. Studies of the BKT transition in cold atoms have stimulated great interest in recent years, but a clear demonstration of critical behaviour near the phase transition has remained elusive. Here we report in situ density and density-fluctuation measurements of two-dimensional Bose gases of caesium at different temperatures and interaction strengths, observing scale-invariant, universal behaviours. The extracted thermodynamic functions confirm the existence of a wide universal region near the BKT phase transition, and provide a sensitive test of the universality predicted by classical-field theory and quantum Monte Carlo calculations. Our experimental results provide evidence for growing density-density correlations in the fluctuation region, and call for further explorations of universal phenomena in classical and quantum critical physics.

Original languageEnglish (US)
Pages (from-to)236-240
Number of pages5
JournalNature
Volume470
Issue number7333
DOIs
StatePublished - Feb 10 2011

All Science Journal Classification (ASJC) codes

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    Hung, C. L., Zhang, X., Gemelke, N., & Chin, C. (2011). Observation of scale invariance and universality in two-dimensional Bose gases. Nature, 470(7333), 236-240. https://doi.org/10.1038/nature09722