General phase diagram features of superradiant phase transitions

Abstract: Various light-matter interactions lead to diverse phase diagram structures in superradiant phase transition (SPT) studies. Such systems consist of multiqubit and multimode with anisotropic couplings, one-photon and two-photon interactions, Stark shifts, inter-cavity hoppings, qubit-qubit interactions and so on. We find a general phase diagram feature that the origin is in normal phase (NP) and SPT happens only once along the radial direction of a chosen coupling parameter vector with the mean-field method at finite temperature. We can calculate the the phase boundary and SPT properties by a concise method. We illustrate it with specific models and find SPT can be achieved in strong coupling regime by means of multimode collective behavior.