2004/02/29 by M. Arlego, Marcelo Arlego, Wilhelm Brenig +7 · 1 citation
Physics and Astronomy · #Magnetic properties of thin films #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #cond-mat.dis-nn #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.70.014436
published as Phys. Rev. B 70, 014436 (2004) · 9 pages REVTeX4 including 7 figures, final version; Fig. 5 modified
openalex publication_date 2004/07/30 · arxiv created 2004/08/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We discuss the effect of weak bond disorder in two-leg spin ladders on the dispersion relation of the elementary triplet excitations with a particular focus on the appearance of bound states in the spin gap. Both the cases of modified exchange couplings on the rungs and the legs of the ladder are analyzed. Based on a projection on the single-triplet subspace, the single-impurity and small cluster problems are treated analytically in the strong-coupling limit. Numerically, we study the problem of a single impurity in a spin ladder by exact diagonalization to obtain the low-lying excitations. At finite concentrations and to leading order in the inter-rung coupling, we compare the spectra obtained from numerical diagonalization of large systems within the single-triplet subspace with the results of diagrammatic techniques, namely, low-concentration and coherent-potential approximations. The contribution of small impurity clusters to the density of states is also discussed.