the invitation

Invitation to Seminar Talk
Gaussian fluctuations in the two-dimensional
BCS-BEC crossover
Giacomo Bighin
University of Padua
Host: Misha Lemeshko
Motivated by very recent experimental results [1,2] concerning the realization of a quasi-twodimensional Fermi gas with widely tunable interaction due to a Feshbach resonance, along with
the measurement of the equation of state and of the Berezinskii- Kosterlitz-Thouless critical
temperature, we investigate the two-dimensional BCS-BEC crossover using a path integral
formulation [3].
The role of fluctuations is enhanced in lower dimensionality systems: we show that in the present
case the inclusions of Gaussian fluctuations for the order parameter is needed in order to get
reliable results in the BEC regime and quantitative agreement with experiments.
Using a beyond mean-field equation of state we calculate the first and second sound velocities,
showing that in the intermediate and strong coupling regimes the result is radically different with
respect to its mean-field counterpart. In the case of the first sound the theoretical findings are
compared with preliminary experimental data.
We also calculate the Berezinskii-Kosterlitz-Thouless critical temperature: we find that the
inclusion of bosonic collective excitations to the normal density of the system strongly modifies
the result in the intermediate and strongly-coupled regimes, where our theory shows good
agreement with recently reported experimental data.
[1] P. A. Murthy et al., Phys. Rev. Lett. 115, 010401 (2015).
[2] I. Boettcher et al., Phys. Rev. Lett. 116, 045303 (2016).
[3] G. Bighin and L. Salasnich, Phys. Rev. B 93, 014519 (2016).
April 6, 2016, 11:00am
Mondi 2, Central Building, ground floor
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