Thermodynamics of an Impurity Coupled to a Heisenberg Chain: Density-Matrix Renormalization Group and Monte Carlo Studies

Abstract

By extending White's density-matrix renormalization group (DMRG) techniqueto finite temperatures, we calculate the impurity susceptibility for the following systems: (a) a spin-1/2 impurity coupled to a single site of an antiferromagnetic Heisenberg spin-1/2 chainand (b) an impurity coupled symmetrically to the two spins atthe open ends of the chain. We also perform a Monte Carlo simulationand show that the DMRG adaptation gives reliable results.The calculated impurity susceptibility showsPauli-like behavior at low temperatures in the former casewhile a ln T divergence is found in the latter case, in agreement with predictions based on conformal field theory.