Disordered Ground‐State Properties of the Double‐Layer Antiferromagnetic Quantum XXZ Model

Abstract

The double-layer antiferromagnetic quantum XXZ model is studied by the bond-operator meanfield theory. The transverse and longitudinal modes in excited spectra, and the phase diagram for disorder-order phase transition about D and J/J ? , which are the relative strength of spin anisotropy and the ratio of the intralayer coupling to the interlayer coupling, respectively, are obtained. It is found that the critical ratio of (J/J ? ) c is 0.174 for XY model (D = 0), and is 0.430 for isotropic model (D = 1). In the disordered phase and on the critical points, the excitation spectra are analyzed. The spin gap from the condensed spin singlets to the first excited states, the ground state energy and the spin wave velocities in the disordered state are calculated as functions of parameters D and J/J ? .

Ground state behaviors of four‐sublattice ferromagnetic–antiferromagnetic double layers

“…Systems consisting of alternating ferromagnetic and antiferromagnetic layers show many different phases and interesting canting transitions in a magnetic field [12,13]. The ground state properties of double layers have been studied by various methods, including quantum Monte Carlo simulations [14], Schwinger series expansions [15] and the bond-operator meanfield theory [16].…”