QUANTUM VECTOR SPIN-GLASS MODELS IN AN APPLIED FIELD

We use the static approximation to investigate the phase diagram of the infinite-ranged quantum Heisenberg spin glass (QHSG) in an external field, as well as the phase diagram of a two-component quantum spin glass (QXYSG) in a transverse or a longitudinal field. For the QHSG we find that, for strong field (H) and low temperature (T), the phase transition into the spin-glass phase characterized by nonzero transverse spin-glass ordering is given by T(c) approximately exp[-H-2/(2J2S2)], as compared with T(c) approximately exp{-H-2/[2J2S(S + 1)]} for classical spins of magnitude square-root S(S + 1). In the case of QXYSG in a transverse field (GAMMA), the phase boundary terminates at GAMMA/J = 2 for T = 0.