Spin dynamics for the t-J model

The spin dynamics at finite temperature for the t-J model in the underdoped and optimally doped regimes is studied within the fermion-spin theory. It is shown that the dynamical spin structure factor spectrum at the antiferromagnetic wave vector Q = (pi, pi) is separated into low-and high-frequency parts, respectively, but the high-frequency part is suppressed in the dynamical susceptibility spectrum chi "(Q,omega), while the low-frequency part is temperature dependent, which is in qualitative agreement with experiments and numerical simulations. (C) 1998 Elsevier Science B.V.