Transport in Almost Integrable Models: Perturbed Heisenberg Chains

摘要: The heat conductivity kappa(T) of integrable models, like the one-dimensional spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite temperatures as a consequence conservation laws associated with integrability. Small perturbations lead to but large transport coefficients which we calculate perturbatively using exact diagonalization and moment expansions. We show that there are two different classes perturbations. While an interchain coupling strength J(perpendicular) leads proportional 1/J(perpendicular)2 expected from simple golden-rule arguments, obtain much larger 1/J'4 for weak next-nearest-neighbor interaction J'. This can be explained by new approximate law J-J' chain.