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Using the spin-wave approximation elementary excitations of a semi-infinite two-dimensional S=½ 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 [1]. To investigate how the above crystal partitioning influences on the carriers, we calculate the hole spectral function of the t-J model using the spin-wave and noncrossing approximations. In the case of small hole concentrations and strong correlations, |t|>>J, several near-boundary site rows appear to be depleted of holes. The reason is a deformation of the magnon cloud, which surrounds the hole, near the boundary. The hole depletion leads to a more complicated spectral function in the boundary row in comparison with its bulk shape. This is a consequence of a difference in the spectral functions for near-boundary rows - replicas of maxima from these rows are seen in the boundary spectral function [2]. The discrepancies between the photoemission data of a number of transition-metal oxides and calculated bulk spectra may be connected with this process.
1. N. Voropajeva and A. Sherman, Modern Phys. Lett. B 24, 2327 (2010). 2. A. Sherman and N. Voropajeva, J. Phys.: Condens. Matter 22, 375603 (2010). |
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