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

Abstract

Nearest-neighbor spin correlations are considered near the surface of a semi-infinite spin-1 2 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.

Thet–Jmodel on a semi-infinite lattice

“…From the similarity of the 2D and 3D magnon spectra 11,12 we can expect to obtain analogous results for charge carriers in a 3D crystal with strong electron correlations. From these results, the conclusion can be drawn that the surface electronic structure, which is tested by the photoelectron and tunnel spectroscopies, even in the considered case of the idealized surface may essentially differ from the bulk spectrum.…”

“…3. The spectral function without this mode was calculated with the magnon Green's function (13) instead of the full function (12). As seen from the figure, the near-boundary mode makes its contribution in the location of the maximum and the intensity redistribution.…”

“…Their peak dominates in the spectral intensity −ImD(k y ωl x l x ) for l x = 0, 1 and practically disappears in site rows more distant from the boundary. 11,12 It is instructive to elucidate how the equations obtained above are transformed to the form for an unbounded crystal with distance from the boundary. In Eq.…”

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

“…Apart from them Green's functionD(k y ωl x l ′ x ) may have poles connected with the second term in the right-hand side of Eq. (7). The imaginary parts of Green's functionsD (0) (k y ωl x l ′ x ) andD(k y ωl x l ′ x ) are shown in Figs.…”

“…The two rows near the edge are the location of the mode connected with the pole of the second term in Eq. (7). This mode has the dispersion ω(k y ) = √ 2J |sin (k y )| and is termed the boundary spin-wave mode.…”