Magnetic properties of the doped two-dimensional antiferromagnet

The variety of the normal-state magnetic properties of cuprate high-Tc superconductors is interpreted based on the self-consistent solution of the self-energy equations for the two-dimensional t-J model. The observed variations of the spin correlation length with the hole concentration x, of the spin susceptibility with x and temperature T and the scaling of the static uniform susceptibility are well reproduced by the calculated results. The nonmonotonic temperature dependence of the Cu spin-lattice relaxation rate is connected with two competing tendencies in the low-frequency susceptibility: its temperature decrease due to the increasing spin gap and the growth of the susceptibility in this frequency region with the temperature broadening of the maximum in the susceptibility.Comment: 6 pages, 5 figures, Proc. Int. Conf. "Modern Problems of Superconductivity", 9-14 Sept. 2002, Yalta, Ukrain

Two-dimensional t-J model at moderate doping

Using the method which retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic ordering, spectral and magnetic properties of the two-dimensional t-J model in the normal state are investigated for the ranges of hole concentrations 0 <= x <= 0.16 and temperatures 0.01t <= T <= 0.2t. The used hopping t and exchange J parameters of the model correspond to hole-doped cuprates. The obtained solutions are homogeneous which indicates that stripes and other types of phase separation are not connected with the strong electron correlations described by the model. A series of nearly equidistant maxima in the hole spectral function calculated for low T and x is connected with hole vibrations in the region of the perturbed short-range antiferromagnetic order. The hole spectrum has a pseudogap in the vicinity of (0,\pi) and (\pi,0). For x \approx 0.05 the shape of the hole Fermi surface is transformed from four small ellipses around (\pm\pi/2,\pm\pi/2) to two large rhombuses centered at (0,0) and (\pi,\pi). The calculated temperature and concentration dependencies of the spin correlation length and the magnetic susceptibility are close to those observed in cuprate perovskites. These results offer explanations for the observed scaling of the static uniform susceptibility and for the changes in the spin-lattice relaxation and spin-echo decay rates in terms of the temperature and doping variations in the spin excitation spectrum of the model.Comment: 12 pages, 14 figure