Abstract

We present our recent progress on the exploration of the phase transition from a normal to a condensed phase in a strongly interacting two-dimensional Fermi gas. We use a matter-wave focusing technique to directly access the momentum distribution of the system and observe the emergence of a condensate at low temperatures. We obtain the phase diagram of the two-dimensional Fermi gas in the BEC -BCS crossover by tuning the temperature and the interaction strength of the system. From the momentum distribution, we extract the g1 correlation function of the sample which clearly shows a region of algebraically decaying phase coherence for scales exceeding the thermal correlation length. This is consistent with the theoretical predictions for a Berezinsky–Kosterlitz–Thouless (BKT)-like phase. This observation is further supported by a self-interference measurement which also exhibits quasi long-range phase coherence.