The antiferromagnetic spin-1/2 Heisenberg model on the square lattice in a magnetic field

TL;DR

This study uses exact diagonalizations to analyze how magnetic fields influence the spin dynamics and properties of the antiferromagnetic spin-1/2 Heisenberg model on a square lattice, providing insights relevant to neutron scattering experiments.

Contribution

It offers a detailed analysis of the field-dependent dynamical spin correlations and microscopic parameters of the model, including the effects of quantum fluctuations and magnon stability.

Findings

Magnons are well defined at low fields across the Brillouin zone.

Quantum fluctuations significantly modify the magnon dispersion.

Magnons become unstable at higher fields due to multi-magnon decay channels.

Abstract

We study the field dependence of the antiferromagnetic spin-1/2 Heisenberg model on the square lattice by means of exact diagonalizations. In a first part, we calculate the spin-wave velocity, the spin-stiffness, and the magnetic susceptibility and thus determine the microscopic parameters of the low-energy long-wavelength description. In a second part, we present a comprehensive study of dynamical spin correlation functions for magnetic fields ranging from zero up to saturation. We find that at low fields, magnons are well defined in the whole Brillouin zone, but the dispersion is substantially modified by quantum fluctuations compared to the classical spectrum. At higher fields, decay channels open and magnons become unstable with respect to multi-magnon scattering. Our results directly apply to inelastic neutron scattering experiments.