Cluster states of Fermions in the single l-shell model
  The paper concerns the ground state structure of the partly filled l-shell of a fermionic gas of atoms of spin s in a spherically symmetric spin independent trap potential. At particle numbers N=n(2s+1), n=1,2,...,2l+1 the basic building blocks are clusters consisting of (2s+1) atoms, whose wave functions are completely symmetric and antisymmetric in space and spin variables, respectively. The creation operator of a cluster is constructed whose repeated application to the vacuum leads to the multi-cluster state. Ground state energy expressions are derived for the n-cluster states at different l,s values and interpreted in simple terms. 
Andras Csordas, Eva Szoke, and Peter Szepfalusy