Will a bose-condensed exciton gas be superfluid?

For a system of Bose-condensed Wannier excitons, the second reduced density matrix for electrons and holes is shown to have the property of off-diagonal long-range order (ODLRO). From the equation of motion for this density matrix, we derive the conservation laws which are relevant for a condensed exciton system. These equations are obtained by projecting the electron-hole density matrices into the exciton space. From the conservation laws, a two-fluid model follows, which describes the superfluid flow of the excitation energy.