https://doi.org/10.1140/epjd/e2011-20084-5
Regular Article
Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases
1
ICFO-Institut de Ciencies Fotoniques, 08860
Castelldefels (Barcelona),
Spain
2
Física Teorica: Informació i Processos Quàntics, Universitat
Autònoma de Barcelona, 08193
Bellaterra,
Spain
3
Department of Physics and Astronomy, University of
Aarhus, 8000
Aarhus C,
Denmark
a e-mail: pietro.massignan@icfo.es
Received:
31
January
2011
Received in final form:
18
May
2011
Published online:
27
July
2011
We analyze the properties of a single impurity immersed in a Fermi sea. At positive energy and scattering lengths, we show that the system possesses a well-defined but metastable excitation, the repulsive polaron, and we calculate its energy, quasiparticle residue and effective mass. From a thermodynamic argument we obtain the number of particles in the dressing cloud, illustrating the repulsive character of the polaron. Identifying the important 2- and 3-body decay channels, we furthermore calculate the lifetime of the repulsive polaron. The stability conditions for the formation of fully spin polarized (ferromagnetic) domains are then examined for a binary mixture of atoms with a general mass ratio. Our results indicate that mass imbalance lowers the critical interaction strength for phase-separation, but that very short quasiparticle decay times will complicate the experimental observation of itinerant ferromagnetism. Finally, we present the spectral function of the impurity for various coupling strengths and momenta.
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2011