  Following the experimental realization of Dicke superradiance in Bose gases
coupled to cavity light fields, we investigate the behavior of ultra cold
fermions in a transversely pumped cavity. We focus on the equilibrium phase
diagram of spinless fermions coupled to a single cavity mode and establish a
zero temperature transition to a superradiant state. In contrast to the bosonic
case, Pauli blocking leads to lattice commensuration effects that influence
self-organization in the cavity light field. This includes a sequence of
discontinuous transitions with increasing atomic density and tricritical
superradiance. We discuss the implications for experiment.
