Integrability and Ideal Conductance at Finite Temperatures

We analyze the finite temperature charge stiffness D (T>0), using a generalization of Kohn's method, for the problem of a particle interacting with a fermionic bath in one dimension. We present analytical evidence, using the Bethe ansatz method, that D (T>0) is finite in the integrable case where the mass of the particle equals the mass of the fermions and numerical evidence that it vanishes in the nonintegrable case of unequal masses. We conjecture that a finite D (T>0) is a generic property of integrable systems.