Ultracold Atomic Seminar - Henning Moritz: Superfluidity and coherence in 3D and 2D Fermi and Bose systems
Oplysninger om arrangementet
Superfluidity, condensation and coherence are intimately connected. In 3D systems such as bulk 4He and conventional superconductors, frictionless flow emerges as the bosonic atoms or Cooper pairs condense into a macroscopic wavefunction exhibiting true long range order. In the first part of the talk I will present an experiment in which we map out the critical velocity of a flat three-dimensional superfluid in the crossover from Bose-Einstein condensation to Bardeen-Cooper-Schrieffer superfluidity.
In the second part, I will focus on the coherence in two-dimensional superfluids, which show a strikingly different behavior than their 3D counterpart: While true long-range order in 2D systems is precluded by thermal fluctuations, Berezinskii-Kosterlitz-Thouless (BKT) theory predicts that 2D systems can still become superfluid with a first order correlation function g1(r) that decays algebraically with distance r with a temperature-dependent scaling exponent tau. I will present experimental results of a local coherence measurement of a strongly interacting 2D Bose gas, which allows us to determine the scaling exponent as a function of phase space density and extract the superfluid density.