Incommensurate Spin Dynamics in Underdoped Cuprate Perovskites

摘要

The incommensurate magnetic response observed in normal-state cuprate perovskites is interpreted based on Mori's projection operator formalism and the t-J model of Cu-O planes. In agreement with experiment, the calculated dispersion of maxima in the susceptibility has the shape of two parabolas with upward- and downward-directed branches which converge at the antiferromagnetic wave vector. The upper parabola reflects the dispersion of magnetic excitations of the localized Cu spins, while the lower parabola arises due to the weakness of the interaction between the spin excitations and holes near the hot spots. Also, in conformity with experiment, the low-frequency incommensurability parameter δ grows with the hole concentration x for x≤0.12 and then saturates. It is conjectured that the dissimilarity of the susceptibility frequency dependencies in yttrium and lanthanum cuprates may be connected with different values of the hole bandwidth and damping in these crystals.