Noise power spectrum for tunneling through a quantum dot in the Kondo Regime

The charge-current and spin-current noise spectra are calculated for tunneling through an ultrasmall quantum dot in the Kondo regime. Modeling the dot by an infinite-U Anderson model, we use the noncrossing approximation to formulate the current-current correlation function for arbitrary frequency and voltage bias. Our formulation fulfills all the basic requirements of the current-current correlation function, including current conservation and the recovery of the fluctuation-dissipation theorem at zero frequency and bias. The full temperature, voltage-bias and frequency dependences of the noise are analyzed, and the significance of the Kondo correlations that develop are discussed. Deficiencies of the slave-boson mean-field approach for calculating the noise are pointed out.