Competition between superconductivity and the pseudogap phase in the t – J model

The t – J model in the large N limit ( N denotes the number of spin components) yields a pseudogap phase in the underdoped region which is related to a d‐wave charge density wave (d‐CDW). We present results for the doping dependence of the superconducting and d‐CDW order parameters as well as for collective excitations in the presence of these two order parameters. We argue that the electronic Raman spectrum with B 1g symmetry probes the amplitude fluctuations of the d‐CDW at zero momentum.