Supershell structure in trapped dilute Fermi gases

Abstract

We show that a dilute harmonically trapped two-component gas of fermionic atoms with a weak repulsive interaction has a pronounced super-shell structure: the shell fillings due to the spherical harmonic trapping potential are modulated by a beat mode. This changes the ``magic numbers'' occurring between the beat nodes by half a period. The length and amplitude of this beating mode depend on the strength of the interaction. We give a simple interpretation of the beat structure in terms of a semiclassical trace formula for the symmetry breaking U(3) --> SO(3).Comment: 4 pages, 4 figures; In version 2, references added. The semiclassical explanation of super-shell structure is refined. Version 3, as appeared in Phys. Rev.