Spin correlations near the surface of a three-dimensional Heisenberg antiferromagnet

TL;DR

This paper investigates how spin correlations behave near the surface of a three-dimensional Heisenberg antiferromagnet, revealing enhanced correlations and a surface-specific excitation spectrum using spin-wave approximation.

Contribution

It provides a detailed analysis of surface spin correlations and excitation modes in a 3D Heisenberg antiferromagnet, extending understanding from 2D to 3D systems.

Findings

Surface spin correlations are stronger than bulk correlations.

Surface excitations include standing spin waves and surface-specific modes.

Surface region exhibits a comb-like pattern of correlations.

Abstract

Nearest-neighbor spin correlations are considered near the surface of a semi-infinite spin-$\frac12$ Heisenberg antiferromagnet on a simple cubic lattice. In the spin-wave approximation, the excitation spectrum of this model involves bulk modes -- standing spin waves and a quasi-two-dimensional mode of surface spin waves. These latter excitations eject the bulk excitations from the surface region thus dividing the antiferromagnet into two parts with different excitations. As a result absolute values of the spin correlations near the surface exceed the bulk value. In the surface region, the pattern of spin correlations resembles the comb structure recently obtained for the two-dimensional case.