Boundary defect in a spin ladder

Abstract

The integrable su(1|3)-invariant spin-ladder model with boundary defect is studied using the Bethe ansatz method. The exact phase diagram for the ground state is obtained and the boundary quantum critical behavior is discussed. It consists of a gapped phase in which the rungs of the ladder form singlet states and a gapless Luttinger liquid phase. Depending on the boundary potential of the first rung a boundary bound state may occur. If populated at low temperatures this bound state represents a localized magnetic moment of spin one. In the Luttinger liquid phase the local moment is screened at low temperatures in analogy to the Kondo effect.