Hannover 2016 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 53: Quantum Gases: Fermions I

Q 53.8: Vortrag

Donnerstag, 3. März 2016, 16:15–16:30, e001

Measuring the scaling exponent of strongly interacting 2D gases — •Jonas Siegl, Niclas Luick, Klaus Hueck, Wolf Weimer, Kai Morgener, Thomas Lompe, and Henning Moritz — Institut für Laserphysik,Hamburg, Deutschland

The critical behaviour exhibited by two-dimensional systems has profound impact on phenomena ranging from superfluidity in liquid helium films to high temperature superconductivity. It is intriguing that 2D systems with a continuous symmetry can become superfluid at all, since true long-range order is precluded by thermal fluctuations. Instead, the celebrated Berezinskii, Kosterlitz and Thouless (BKT) theory predicts that below the superfluid transition the first order coherence decays algebraically with no characteristic length scale. Such scale free behaviour is typically only encountered at the critical point, whereas in 2D systems it is predicted to persist down to zero temperature, making them critical throughout.

Here, we locally probe the phase fluctuations of strongly correlated 2D gases of composite bosons. We determine the scaling exponent characterising the algebraic decay as a function of phase space density: during a short expansion along the strongly confined direction the phase fluctuations responsible for the algebraic decay are transformed into density fluctuations. We image the resulting density distribution and extract the scaling exponent from the power spectrum. The results are in excellent agreement with BKT theory, from which we can deduce the superfluid density locally. Our results extend the study of BKT theory towards the strongly interacting regime of ferminonic superfluidity.