‘Baryonic’ bound-state instability in trapped fermionic atoms

Sympathetic cooling of trapped fermionic gases [1] is likely to lead to the creation of degenerate Fermi gases in the near future. In magnetic traps, the fermion’s spin is locked to the field direction. However the advent [2,3] of optical traps holds the promise of degenerate Fermi gases with unquenched spins and hence a variety of nonideal Fermi gases. Already there has been some discussion of the possibility of pairing [4–6] in the presence of attractive interactions, which may be of an exotic type [7,8]. In part the exotic possibilities occur because alkali fermions exist which have larger total spins than spin 1/2: Na, Rb, Cs, Cs, Cs have S = 5/2, 5/2, 3/2, 7/2, 9/2 respectively [9]. In this paper we will point out that in addition to pairing there are other possible ground states, in particular when the atoms experience spin-independent attractive interactions. One-dimensional models of interacting fermions with spins greater than one half have been considered for a substantial time, both for repulsive [10] and attractive [11–13] inter-