Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas

Abstract

We experimentally investigate the first-order correlation function of a trapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a transition to a low-temperature superfluid phase with algebraically decaying correlations. We show that the spatial coherence of the entire trapped system can be characterized by a single temperature-dependent exponent. We find the exponent at the transition to be constant over a wide range of interaction strengths across the crossover. This suggests that the phase transitions in both the bosonic regime and the strongly interacting crossover regime are of Berezinskii-Kosterlitz-Thouless-type and lie within the same universality class. On the bosonic side of the crossover, our data are well-described by Quantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly interacting regime, we observe a superfluid phase which is significantly influenced by the fermionic nature of the constituent particles.

9 pages, 5 figures

References in corpus (7)

• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Weakly bound dimers of fermionic atoms
• Observation of scale invariance and universality in two-dimensional Bose gases
• Superfluid behaviour of a two-dimensional Bose gas
• Observation of pair condensation in the quasi-2D BEC-BCS crossover
• Kosterlitz-Thouless transition of the quasi two-dimensional trapped Bose gas
• Matter wave Fourier optics with a strongly interacting two-dimensional Fermi gas

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