Bond-Operator Mean Field Theory for the Bilayer Heisenberg Model

TL;DR

This paper develops a bond-operator mean field theory for the bilayer Heisenberg model, providing insights into quantum critical regions and comparing with other methods.

Contribution

It introduces a novel mean field approach for the bilayer Heisenberg model and analyzes quantum critical regions near phase transitions.

Findings

Quantum critical region is narrower than previously thought.

Mean field results agree with strong-coupling expansions near critical points.

Field-induced transitions occur at lower temperatures than earlier estimates.

Abstract

Bond-operator mean field equations for the square-lattice, S=1/2 bilayer Heisenberg model are developed and solved numerically. In the vicinity of both the zero-field critical point and the field-induced transitions, comparisons are made with T=0 and finite-temperature strong coupling expansions. The mean-field theory suggests that the quantum critical region for the field-induced transitions is restricted to significantly lower temperatures than one might have concluded based on strong-coupling expansions or other numerical studies.