Discontinuities in the First and Second Sound Velocities at the Berezinskii-Kosterlitz-Thouless Transition

Abstract

We calculate the temperature dependence of the first and second sound velocities in the superfluid phase of a 2D dilute Bose gas by solving Landau's two fluid hydrodynamic equations. We predict the occurrence of a significant discontinuity in both velocities at the critical temperature, as a consequence of the jump of the superfluid density characterizing the Berezinskii-Kosterlitz-Thouless transition. The key role of the thermal expansion coefficient is discussed. We find that second sound in this dilute Bose gas can be easily excited through a density perturbation, thereby, making the perspective of the measurement of the superfluid density particularly favorable.

5 pages, 5 figures, published version

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• Observation of scale invariance and universality in two-dimensional Bose gases
• Radiofrequency spectroscopy of a strongly interacting two-dimensional Fermi gas
• Superfluid behaviour of a two-dimensional Bose gas
• Universal thermodynamics of a two-dimensional Bose gas
• First and second sound in a highly elongated Fermi gas at unitarity

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