Spin-dependent shot noise in ferromagnet/quantum dot/ferromagnet tunneling system

We study the shot noise spectrum of the system composed of a semiconductor quantum dot coupled to two ferromagnetic leads with arbitrary relative magnetization direction. A general formula for the spin-dependent noise spectrum is obtained within the formalism of the nonequilibrium Green functions. We show that the noise spectrum and Fano factor can increase or decrease with the relative angle between the magnetizations of the two leads, which depends on the system parameters. The spin current correlations strongly depend on the spin orientations and show a nonmonotonic behavior versus the relative magnetization angle.