Nonmagnetic Impurities in Spin Gap Systems

Abstract

The effect of nonmagnetic impurities in the two-leg Heisenberg ladder system and other spin liquids with excitation gap is discussed. It is shown that the random depletion of spins introduces a random Berry phase term into the nonlinear σ model. The classical nature of the antiferromagnetic correlation is enhanced by the topological decoherence, and the staggered susceptibility shows more singular behavior at low temperatures than the uniform antiferromagnetic Heisenberg chain.