Photon-assisted thermoelectric properties of noncollinear spin valves

Abstract

We report theoretical analysis of thermal-spin and thermoelectric properties of noncollinear spin valves driven by a high-frequency ac voltage bias. The spin valve consists of two ferromagnetic contacts sandwiching a single-level or multilevel quantum dot (QD). A general formulation for the time-averaged thermal-spin and thermoelectric properties of spin valves is derived within the nonequilibrium Green's function theory, which provides a starting point for further numerical calculations of these properties. Numerical results of a spin valve having a spin-degenerate single-level QD are given as an example. The ac bias induces various photon-assisted transmission peaks which can greatly enhance the Seebeck coefficients and the figures of merit, and offer a new possibility to tune both the spin-dependent and normal thermoelectric properties of the spin valve. Details of these properties and how they depend on the noncollinearity of the spin valve, magnetic polarization, ac frequency, ac bias, and other control parameters are reported. A particularly interesting result is the opposite dependency of the thermoelectric properties on the magnetic polarization and noncollinearity for contacts with or without spin accumulation.