Disordered ground-state properties of a double-layer Heisenberg antiferromagnet

Abstract

The disordered ground-state properties of a double-layer quantum antiferromagnet are investigated in the bond operator representation. The intralayer and interlayer couplings are J and Jperpendicular to , respectively. In a mean-field approximation, we obtain a spin gap which decreases with increasing ratio lambda =J/Jperpendicular to and disappears at the value lambda c=0.292. In the region 0<or= lambda <or= lambda c, we calculate the disordered ground-state energy, the intralayer and interlayer nearest-neighbour singlet strengths, and the correlation length.