Magnetization plateaux in one-dimensional random quantum magnets

The effect of randomness on the magnetization plateaux in frustrated S=1/2 Heisenberg chains is studied by the DMRG method. It is shown that the random mixture of two kinds of chains with plateaux due to spontaneous translational symmetry breakdown at Ms/2 (Ms: the full magnetization) does not show a plateaux at Ms/2. In the S=1/2 frustrated Heisenberg chains with bond alternation and random sign strong bonds, the plateau at Ms/2 splits by randomness while an additional plateau is generated at M=(1-p)Ms