Bound states in weakly disordered spin ladders

M. ARLEGO, W. BRENIG, D.C. CABRA, F. HEIDRICH-MEISNER, A. HONECKER, G. ROSSINI

PHYSICA B - CONDENSED MATTER

ELSEVIER SCIENCE BV

Año: 2005 vol. 359 p. 1424 - 1426

0921-4526

We study the appearance of bound states in the spin gap of spin-1/2 ladders induced by weak bond disorder. Starting from the strong-coupling limit, i.e., the limit of weakly coupled dimers, we perform a projection on the single-triplet subspace and derive the position of bound states for the single impurity problem of one modified coupling as well as for small impurity clusters. The case of a finite concentration of impurities is treated with the coherent-potential approximation in the strong-coupling limit and compared with numerical results. Furthermore, we analyze the details in the structure of the density of states and relate their origin to the influence of impurity clusters.