From BEC polaron to BCS polaron

May 18, 2016, 2:45 PM
8h 15m



Giovanni LOMBARDI (Universiteit Antwerpen)


Ever since the polaron concept was introduced by Landau in 1933 to describe the quasiparticle arising from the interaction between an electron and the polarization cloud it drags along while moving in a polar crystal, a wide variety of physical systems have been mapped on the polaron problem. Among these realizations, one that has been the focus of much attention in the recent years is the BEC polaron: a quasiparticle arising from the interaction of an impurity with the Bogoliubov excitations of a Bose-Einstein condensate. In this presentation we consider the interaction of a single impurity atom with the collective excitations of a fermionic superfluid by mapping it on the same Hamiltonian used in the BEC polaron case. This ansatz is in principle valid only in the extreme BEC side of the Feshbach resonance where the Fermi superfluid becomes in fact a molecular BEC. In the framework of a recently developed effective field theory [1] this molecular condensate is described by a macroscopic wavefunction. The description in terms of a macroscopic wavefunction remains valid also when moving away from the BEC limit and towards unitarity, provided the coefficients of the field equation are properly adapted. This allows to study how the properties of the BEC polaron change when the underlying condensate no longer consists of pointlike bosons, but of Cooper pairs. The polaron problem is then studied in the weak coupling limit by employing the well known T=0 perturbative treatment and the behavior of effective mass and polaronic coupling constant is examined as function of the impurity-boson interaction and of the fermion-fermion interaction in the underlying superfluid [2].

[1] S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015).

[2] G. Lombardi, J. Tempere, arXiv:1604.00776 [cond-mat.quant-gas]

Primary authors

Giovanni LOMBARDI (Universiteit Antwerpen) Jacques TEMPERE (Universiteit Antwerpen)

Presentation materials