Random Bond XXZ Chains with Modulated Couplings

Abstract

The magnetization behavior of q -periodic antiferromagnetic spin- 1 / 2 Heisenberg chains under uniform magnetic fields is investigated in a background of disorder exchange distributions. By means of both real space decimation procedures and numerical diagonalizations in XX chains, it is found that for binary disorder the magnetization exhibits wide plateaus at values of 1 + 2 ( p − 1 ) / q , where p is the disorder strength. In contrast, no spin gaps are observed in the presence of continuous exchange distributions. We also study the magnetic susceptibility at low magnetic fields.