ELFT HÍRADÓ

[Halbritter András <halbritt AT freemail.hu>]

                                        MEGHIVO
                        a BME Fizikai Intezet, Fizika Tanszek
                                     szeminariumara:


                                     Jan Martinek
                           Institute of Molecular Physics,
                              Polish Academy of Sciences,
                                 60-179 Poznan, Poland


                     "Kondo effect in the presence of ferromagnetism
                      in quantum dots coupled to ferromagnetic leads"

Abstract:
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 [1-3]. 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 [2,3]. We extended Wilson’s numerical 
renormalization group method, extended to handle leads with a spin 
asymmetric density of states, to identify the effects of (i) a finite 
spin polarization in the leads at the Fermi surface, (ii) a Stoner 
splitting in the bands governed by the band edges, and (iii) an 
arbitrary shape of the lead 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 molecular systems in contact to ferromagnetic leads 
(ferromagnetic single-molecule transistor) [4]. New experimental results 
for a single carbon nanotube attached to nickel electrodes confirm the 
theoretical predictions [5].

1. J. Martinek, Y. Utsumi, H. Imamura, J. Barnas, S. Maekawa, J. König, 
and G. Schön,     Phys. Rev. Lett. 91, 127203 (2003);
2. J. Martinek, M. Sindel, L. Borda, R. Bulla, J. König, G. Schön, S. 
Maekawa, and J. von Delft, Phys. Rev. Lett. 91, 247202 (2003); Phys. 
Rev. B 72, 121302 (2005).
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. 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).
5. J. R. Hauptmann, J. Paaske, and P.E. Lindelof, Nature Physics, (2008).

        Helye: BME Fizikai Intezet, Fizika Tanszek
                  Budafoki ut 8.
                  F-epulet, III. lepcsohaz, 2. em. 13. előadóterem
                

        Ideje: 2010. februar 2. kedd, 10:15.

        Minden erdeklodot szivesen latunk.

                                                                              
  Halbritter András

Budapest University of Technology and Economics
Department of Physics
1111 Budapest Budafoki út 8.
Tel: +36 1 4631650
Fax: +36 1 4634180