ZERO AND FINITE-TEMPERATURE PHASE-DIAGRAM OF THE SPINLESS FERMION MODEL IN INFINITE DIMENSIONS

The phase diagram of the model of spinless fermions with repulsive nea rest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions (d --> infinity). In spite of its simpl icity the model displays a rich phase diagram depending on the doping delta, the interaction U and the temperature T. The system can be in t he homogeneous phase (HOM), the nonsegregated AB charge density wave ( AB-CDW), the AB phase separation region (PS-AB/HOM; coexistence of AB- CDW and HOM), the incommensurate phase (IP) or the IP phase separation region (PS-BB/IP; coexistence of AB-CDW and IP). We identify three im portant values of the interaction U-IPL = 0.572 < U-IPH = 1.914 < U-IP /PS = 4.212 which distinguish four intervals of U. These imply four di fferent types of phase diagrams. In all the three phase diagrams with U below U-IP/(PS) the IP appears. We propose a new general ansatz for the order parameter of this phase. A competition between the IP, the P S-AB/IP and the PS-AB/HOM is found. The relevance of our findings for the phase scenario of the Hubbard model is shown.