Scaling and Universality in the Anisotropic Kondo Model and the Dissipative Two-State System

Scaling and universality in the Ohmic two-state system is investigated by exploiting the equivalence of this model to the anisotropic Kondo model. For the Ohmic two-state system, we find universal scaling functions for the specific heat C_α(T), static susceptibility χ_α(T), and spin relaxation function S_α(ω), depending on the reduced temperature T/Δ_r (frequency ω/Δ_r), with Δ_r the renormalized tunneling frequency, and uniquely specified by the dissipation strength α ( 0<α<1). The scaling functions can be used to extract α and Δ_r in experimental realizations.