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.
Observation of scale invariance and universality in two-dimensional Bose gases
Chen-Lung Hung,Xibo Zhang,N. Gemelke,C. Chin
Published 2010 in Nature
ABSTRACT
PUBLICATION RECORD
- Publication year
2010
- Venue
Nature
- Publication date
2010-08-31
- Fields of study
Medicine, Physics
- Identifiers
- External record
- Source metadata
Semantic Scholar, PubMed
CITATION MAP
EXTRACTION MAP
CLAIMS
CONCEPTS
- berezinskii–kosterlitz–thouless transition
The two-dimensional phase transition associated with vortex unbinding in the Bose gas.
Aliases: BKT transition, BKT phase transition
- caesium
The atomic species used to realize the two-dimensional Bose gases in the experiment.
Aliases: cesium, Cs
- classical-field theory
A theoretical framework used to predict the universal behaviour of the two-dimensional Bose gas near criticality.
Aliases: classical field theory
- density-density correlations
Correlations between density fluctuations at different points in the gas, used here to characterize the fluctuation region.
Aliases: density correlations
- in situ density and density-fluctuation measurements
Measurements performed on the trapped gas without removing it from the experimental setup, recording both local density and its fluctuations.
Aliases: in situ density measurements, density-fluctuation measurements
- quantum monte carlo calculations
Numerical quantum many-body calculations used as a theoretical reference for the expected universal behaviour.
Aliases: QMC calculations
- scale invariance
A property of the measured behaviour in which the relevant observables remain unchanged under rescaling of length or density scales.
Aliases: scale-invariant behaviour
- thermodynamic functions
Experimental thermodynamic quantities extracted from the measurements to characterize the gas near criticality.
Aliases: extracted thermodynamic functions
- two-dimensional bose gases
Quasi-two-dimensional ultracold Bose gases studied in the experiment as the many-body system of interest.
Aliases: 2D Bose gases
- universality
The shared critical behaviour expected to depend on broad features of the system rather than microscopic details.
Aliases: universal behaviour
REFERENCES
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