1/N expansion for two-dimensional quantum ferromagnets

TL;DR

This paper employs a 1/N expansion using a Schwinger boson approach to analyze the magnetization of a two-dimensional quantum ferromagnet, comparing theoretical results with simulations and experiments.

Contribution

It introduces a large N Schwinger boson method for 2D quantum ferromagnets and compares SU(N) and O(N) models with empirical data.

Findings

SU(N) model matches low-temperature data

O(N) model fits moderate/high-temperature data

Calculations include 1/N corrections to mean field

Abstract

The magnetization of a two-dimensional ferromagnetic Heisenberg model, which represents a quantum Hall system at filling factor nu=1, is calculated employing a large N Schwinger boson approach. Corrections of order 1/N to the mean field (N=infinity) results for both the SU(N) and the O(N) generalization of the bosonized model are presented. The calculations are discussed in detail and the results are compared with quantum Monte Carlo simulations as well as with recent experiments. The SU(N) model describes both Monte Carlo and experimental data well at low temperatures, whereas the O(N) model is much better at moderate and high temperatures.