LEVEL CROSSING AND QUANTUM PHASE TRANSITION OF THE XY RING

Abstract

The ground state of a spin-1/2 ring in the Heisenberg XY model is investigated. The spatial correlation and concurrence between an arbitrary nearest-neighbor pair of spins are calculated with different coupling strength, anisotropic parameter and magnitude of the transverse field. Abrupt changes of the correlation and concurrence due to the competition between coupling and alignment are observed. The transition is found to be the direct result of the level crossing of a finite size spin system.