Frustrated spin-1/2 Ising antiferromagnet on a square lattice in a transverse field.

Abstract

We investigate the phase transitions and tricritical behaviors of the frustrated Ising antiferromagnet with first- (J_{1}<0) and second- (J_{2}<0) nearest-neighbor interactions in a transverse field Ω on the square lattice using an effective-field theory with correlations based on a single-spin approximation. We have proposed a functional for the free energy to obtain the phase diagram in the T-R (R=J_{2}/|J_{1}|) or T-Ω planes. It is shown that due to the transverse field the phase transition between ordered and disordered phases changes in the tricritical point (TCP) from the second order to the first order. The longitudinal and transverse magnetizations are also studied for selected values of R and Ω. In particular, the variation of TCP at the ground state in the three-dimensional space is constructed. For some special cases, values of the critical temperature and the critical transverse field have been determined analytically.