Fermion-mediated BCS-BEC Crossover in Ultracold Potassium-40 Gases
  Studies of Feshbach resonance phenomena in fermionic alkali gases have drawn heavily on the intuition afforded by a Fermi-Bose theory which presents the Feshbach molecule as a featureless Bose particle. While this model may provide a suitable platform to explore the lithium-6 system, we argue that its application to potassium-40, where the hyperfine structure is inverted, is inappropriate. Introducing a three-state Fermi model, where a spin state is shared by the open and closed channel states, we show that effects of ``Pauli blocking'' are recorded in the internal structure of the condensate wave function. 
M. M. Parish, B. Mihaila, B. D. Simons, P. B. Littlewood