Polarons and Molecules in a Two-Dimensional Fermi Gas

Details Polarons and Molecules in a Two-Dimensional Fermi Gas Polarons and Molecules in a Two-Dimensional Fermi Gas

2010-11-16

arxiv.org/abs/1011.3729v2

Phys. Rev. A 83, 021603(R) (2011)

Physics

Condensed Matter

Quantum Gases

5 pages, 2 figures, minor changes

Scientific paper

10.1103/PhysRevA.83.021603

We study an impurity atom in a two-dimensional Fermi gas using variational wave functions for (i) an impurity dressed by particle-hole excitations (polaron) and (ii) a dimer consisting of the impurity and a majority atom. In contrast to three dimensions, where similar calculations predict a sharp transition to a dimer state with increasing interspecies attraction, we show that the polaron ansatz always gives a lower energy. However, the exact solution for a heavy impurity reveals that both a two-body bound state and distortions of the Fermi sea are crucial. This reflects the importance of particle-hole pairs in lower dimensions and makes simple variational calculations unreliable. We show that the energy of an impurity gives important information about its dressing cloud, for which both ans\"atze give inaccurate results.

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