paper

Magnetization plateau in the S=1/2 spin ladder with alternating rung exchange

arXiv:cond-mat/0603153 · doi:10.1088/0953-8984/18/40/014

Abstract

We have studied the ground state phase diagram of a spin ladder with alternating rung exchange in a magnetic filed, in the limit where the rung coupling is dominant. In this limit the model is mapped onto an Heisenberg chain in a uniform and staggered longitudinal magnetic fields, where the amplitude of the staggered field is . We have shown that the magnetization curve of the system exhibits a plateau at magnetization equal to the half of the saturation value. The width of a plateau scales as , where in the case of ladder with isotropic antiferromagnetic legs and in the case of ladder with isotropic ferromagnetic legs. We have calculated four critical fields ( and ) corresponding to transitions between different magnetic phases of the system. We have shown that these transitions belong to the universality class of the commensurate-incommensurate transition.

6 pages, 2 figures

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