RELAXATION IN QUANTUM SPIN-GLASSES

The dynamics of a quantum spin glass, which is described by the random -bond-random-field Ising model in a transverse field, Omega, and is in contact with a heat bath, are studied. The model is applicable to dis ordered hydrogen bonded ferroelectrics with Omega representing the tun neling frequency of the protons. A special type of heat-bath coupling is considered where proton tunneling is modulated by the thermal fluct uations but remains coherent. The underlying time evolution operator i s obtained by means of the resolvent expansion method. The long-time d ependence of the polarization, P-+(t), after switching off a uniform f ield is shown to follow a power-law behavior, which is a quantum effec t.