PSEUDOGAPS AND MAGNETIC PROPERTIES OF THE TWO-DIMENSIONALt-J MODEL

The photoemission and magnetic properties of cuprate perovskites have been extensively studied during the last few years, both because of their unusual behaviour and in the hope that they might provide insight into the physical origin of high-temperature superconductivity. Among these properties the pseudogap observed in photoemission [1–3] and the magnetic pseudogap revealed in the static susceptibility and in the spinlattice relaxation rate of normal-state underdoped cuprates [4,5] have attracted considerable attention. A number of different approaches were suggested for the description of the pseudogaps. In particular, in view of the similarity in symmetry and size of the photoemission pseudogap with the superconducting gap, in Refs. [3,6–8] this pseudogap was connected with the superconducting fluctuations existing above Tc. This idea was based on earlier theoretical results of Refs. [9,10]. Another point of view was suggested in Ref. [11] where the energy spectrum of the two-dimensional (2D) t-J model was shown to have a peculiarity which is similar by its properties to the photoemission pseudogap. In accord with Ref. [11] the pseudogap is a consequence of a specific dispersion of the strongly correlated electron system at moderate doping and is not connected with superconducting fluctuations. The discussion of the magnetic pseudogap in doped cuprates is mainly based on scaling arguments [12–14] and on the idea of real-space pairing [15]. In this paper we describe the energy spectrum, including the photoemission pseudogap, and the magnetic properties demonstrating the magnetic pseudogap in a unified approach based on the 2D t-J model widely used for the description of CuO2 planes of cuprate perovskites (the extensive literature on this model is reviewed in Ref. [16]). For the consideration of the paramagnetic state we extend the spin-wave theory with