SPHERICAL MODEL FOR A QUANTUM SPIN-GLASS

Zero temperature phase transitions in the quantum rotor model of disordered, frustrated, and unfrustrated n-component short-range-coupled spin systems are investigated in the spherical limit, n→. We find a transition to a spin glass ordered phase in three dimensions but not in two. We map out the phase diagram as a function of frustration, finding that the ferromagnetic and spin glass critical lines meet at a bicritical point which also terminates a first order line separating the spin glass and ferromagnetic ordered phases. Finite size scaling of numerically obtained exact solutions on finite lattices is used to estimate critical exponents. © 1995 The American Physical Society.