Molecular spintronics: Spin polarized transport through quantum dots and molecules

The manipulation of magnetization and spin is one of the fundamental processes in magneto-electronics and spintronics, providing the possibility of writing information in a magnetic memory, and also because of the possibility of classical or quantum computation using spin. In most situations, this is realized by means of an externally applied nonlocal magnetic field, which is usually difficult to introduce into an integrated circuit. We propose to control the amplitude and sign of the spin-splitting of a quantum dot induced by the presence of ferromagnetic leads, using a gate voltage without further assistance of a magnetic field. We study the effect of a gate voltage on the spin splitting of an electronic level in a quantum dot attached to ferromagnetic in the Kondo regime using a generalized numerical renormalization group technique. We extended Wilson’s numerical renormalization group method, extended to handle leads with a spin asymmetric density of states. We give an analytical description of our numerical results using perturbative scaling analysis and explain how the effect arises due to spin-dependent charge fluctuations. A conceivable realization of proposed system might be carbon nanotubes or other systems as quantum point contacts, semiconducting nanowires in contact to ferromagnetic leads (ferromagnetic single-molecule transistor) and doped ferromagnetic tunnel junctions. New experimental results confirm the theoretical predictions. 1. J. Martinek, Y. Utsumi, H. Imamura, J. Barnas, S. Maekawa, J. König, and G. Schön, Phys. Rev. Lett. 91, 127203 (2003); 2. A. N. Pasupathy, R. C. Bialczak, J. Martinek, J. E. Grose, L. A. K. Donev, P. L. McEuen, and D. C. Ralph, Science 306, 86 (2004). 3. M. Sindel, L. Borda, J. Martinek, R. Bulla, J. König, G. Schön, S. Maekawa, and J. von Delft, Phys. Rev. B 76, 045321 (2007). 4. J. R. Hauptmann, J. Paaske, and P.E. Lindelof, Nature Physics, (2008). 5. M. R. Calvo et al. Nature 458, 1150 (2009). 6. A. Halbritter, P. Makk, Sz. Mackowiak, Sz. Csonka, M. Wawrzyniak, and J. Martinek, Phys. Rev. Lett. 105, 266805 (2010). 7. H. Yang, S.-H. Yang, G. Ilnicki, J. Martinek, and S. S. P. Parkin, (submitted).

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