Spin current noise spectra of interacting quantum dots

We analyze the equilibrium and non-equilibrium frequency-dependent spin current noise and spin conductance through a quantum dot in the local moment regime. Spin current correlations behave markedly differently from charge correlations: First, equilibrium spin correlations are characterized by two universal scaling functions. One of these functions is related to charge correlations, while the other describes cross-spin correlations. We characterize these functions using a combination of perturbative and non-perturbative methods. We find that spin cross-correlations are suppressed at frequencies below the Kondo scale. For asymmetrical quantum dots a dynamical spin accumulation resonance is found at the Kondo energy, $\omega\sim T_K$. At higher temperatures surprising low-frequency anomalies related to overall spin conservation appear in the spin noise, and the Korringa rate plays a special role.

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