The European Physical Journal D

, Volume 65, Issue 1–2, pp 83–89 | Cite as

Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases

  • P. Massignan
  • G. M. Bruun
Regular Article Degenerate Fermi gases

Abstract

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.

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Copyright information

© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • P. Massignan
    • 1
    • 2
  • G. M. Bruun
    • 3
  1. 1.ICFO-Institut de Ciencies FotoniquesCastelldefels (Barcelona)Spain
  2. 2.Física Teorica: Informació i Processos QuànticsUniversitat Autònoma de BarcelonaBellaterraSpain
  3. 3.Department of Physics and AstronomyUniversity of AarhusAarhus CDenmark

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