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

Abstract

Using the spin-wave approximation elementary excitations of a semi-infinite twodimensional S = 1 2Heisenberg 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.

Excitations and spin correlations near the interface of two three-dimensional Heisenberg antiferromagnets

“…For J 3 = 0 the problem reduces to two noninteracting semi-infinite antiferromagnets, which spin excitations were considered in Refs. [7,[9][10][11]. As mentioned in the Introduction, the spectrum of each antiferromagnet consists of a quasi-2D mode of spin waves, which are mainly located in two nearboundary layers, and bulk modes of standing spin waves in the rest of the crystal.…”

“…As indicated in Refs. [9][10][11], in the case of a semi-infinite antiferromagnet the amplified spin correlations in the boundary layer are connected with the quasi-two-dimensionality of the near-boundary mode, which dominates in the spectral function of this layer. It behaves like a 2D antiferromagnet, in which the nearest-neighbor spin correlation is larger in modulus than in a three-dimensional antiferromagnet (0.3346 vs. 0.3005 [16,17]).…”

“…Spin excitations and correlations near this interface were investigated in Refs. [6][7][8][9][10][11]. In particular, it was shown that the antiferromagnet is divided into two regions with different spin excitations [9][10][11].…”

“…[6][7][8][9][10][11]. In particular, it was shown that the antiferromagnet is divided into two regions with different spin excitations [9][10][11]. In the first region, which embraces two near-boundary atomic layers, the excitations have dimensionality one less than the crystal dimensionality.…”