Theoretical interpretation of the variety of spin gap in high-T-c cuprates

Magnetic properties of underdoped high-T-c cuprates characterized by a spin gap are interpreted in a unified scheme based on the mode-mode coupling th eory. By taking one phenomenological relation for the damping rate of the c ollective modes, it takes account of two different types of pseudogap behav ior in spin excitations and spin gap: (I) the damping rate of spin excitati ons decreases as the temperature decreases, but the spin correlation length does not; (II) the spin correlation length itself turns to decrease. In ca se (I), low-energy spectral weights shift to higher energies near the spin gap determined by the super conducting transition temperature, which reprod uces the observed resonance peak. (C) 2000 Elsevier Science Ltd. All rights reserved.