Spin accumulation in ferromagnetic single-electron transistors in the cotunneling regime

We propose a method of direct detection of spin accumulation, which overcomes problems of previous measurement schemes. A spin-dependent current in a single-electron transistor with ferromagnetic electrodes leads to spin accumulation on the metallic island. The resulting spin splitting of the electrochemical potentials of the island, because of an additional shift by the charging energy, can be detected from the spacing between two resonances in the current-voltage characteristics. The results were obtained in the framework of a real-time diagrammatic approach which allows us to study higher-order (co)tunneling processes in the strong nonequlibrium situation.