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SYEM: Symposium Extreme Matter: From Cold Atoms to the Quark Gluon Plasma
SYEM 2: Symposium Extreme Matter II
SYEM 2.1: Vortrag
Mittwoch, 25. März 2015, 14:30–14:45, C/HSO
The BEC-BCS crossover in a two-dimensional system — •Andre Wenz, Martin Ries, Gerhard Zürn, Mathias Neidig, Luca Bayha, Dhruv Kedar, Puneet Murthy, and Selim Jochim — Physikalisches Institut, Universität Heidelberg
In recent years ultracold fermionic systems have been used to explore the three-dimensional BEC-BCS crossover. This crossover smoothly links bosonic superfluidity of dimers with a fermionic superfluid of Cooper pairs. Between these two limits lies the strongly interacting regime where the interaction parameter diverges and the critical temperature for superfluidity reaches a maximum. By freezing out the dynamics in some of the spatial directions, one can tune the dimensionality of the system and this leads to a qualitative change of the key properties of the system. For example, for 2D systems the phase transition to the bosonic superfluid phase is then expected to be driven by the BKT mechanism which leads to a topological phase transition associated with the pairing of vortices. We experimentally explore the 2D BEC-BCS crossover using a Fermi gas of ultracold lithium-6 atoms. We observe the phase transition to a low temperature phase by investigating the system’s pair momentum distribution. On the bosonic side of the crossover, the observed transition temperature and phase coherence is consistent with the theoretical predictions for a BKT-type phase transition. However, where the 2D interaction strength 1/ln(kF a2D) diverges, theoretical prediction become extremely difficult and our measurements offer the first experimental benchmark to challenge and test theoretical models in this complex regime.