Near-Boundary and Bulk Regions of a Semi-Infinite Two-Dimensional Heisenberg Antiferromagnet

TL;DR

This paper analyzes the elementary excitations in a semi-infinite 2D Heisenberg antiferromagnet, revealing boundary and bulk modes, and shows boundary effects enhance nearest-neighbor spin correlations at the edge.

Contribution

It introduces a detailed spin-wave analysis distinguishing boundary and bulk excitations, highlighting boundary-induced modifications in spin correlations.

Findings

Boundary spin waves eject bulk modes from edges

Edge spin correlations exceed bulk values

Boundary effects significantly alter local magnetic properties

Abstract

Using the spin-wave approximation elementary excitations of a semi-infinite two-dimensional $S=\frac12$ Heisenberg antiferromagnet are considered. The spectrum consists of bulk modes -- standing spin waves and a quasi-one-dimensional mode of boundary spin waves. These latter excitations eject bulk modes from two boundary rows of sites, thereby dividing the antiferromagnet into two regions with different dominant excitations. As a result absolute values of nearest-neighbor spin correlations on the edge exceed the bulk value.