Magnon bands of N-leg integer-spin antiferromagnetic systems in the weak interchain-coupling regime

TL;DR

This paper develops a perturbative approach based on the nonlinear sigma model to estimate magnon excitation energies in N-leg integer-spin antiferromagnetic ladders and tubes, confirming the persistence of the Haldane phase in higher dimensions.

Contribution

It introduces a first-order perturbation theory method for calculating magnon energies in coupled spin systems, applicable to various interchain interactions and higher-dimensional models.

Findings

Perturbation theory agrees well with quantum Monte Carlo results.

Supports the existence of a Haldane phase in anisotropic higher-dimensional systems.

Method applicable to other gapped chain systems with known low-energy physics.

Abstract

Using the exact results of the O(3) nonlinear sigma model (NLSM) and a few quantitative numerical data for integer-spin antiferromagnetic (AF) chains, we systematically estimate all magnon excitation energies of N-leg integer-spin AF ladders and tubes in the weak-interchain-coupling regime. Our method is based on a first-order perturbation theory for the strength of the interchain coupling. It can deal with any kind of interchain interactions, in principle. We confirm that results of the perturbation theory are in good agreement with those of a quantum Monte Carlo simulation and with our recent study based on a saddle-point approximation of the NLSM [Phys. Rev. B 72, 104438 (2005)]. Our theory further supports the existence of a Haldane (gapped) phase even in a d-dimensional (d\geq 2) spatially anisotropic integer-spin AF model, if the exchange coupling in one direction is sufficiently strong compared with those in all the other directions. The strategy in this paper is applicable to other N-leg systems consisting of gapped chains which low-energy physics is exactly or quantitatively known.