Résumé des résultats (Abstract)
(Anglais)
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We have analysed two-parameter pumping for classical particles subject to a periodic potential and subject to thermal noise. We have investigated non-linear spin transport in diluted magnetic semiconductor quantum wells. The dynamic stability of field domains in ac-driven super-lattices was investigated.
Two-parameter pumping of classical particles
We have analysed two parameter pumping for classical Brownian particles subject to a periodic potential [1]. We treat the case of a spatially symmetric potential. To generate a current it is then necessary that the pumping potential breaks both the temporal and spatial symmetry. For the case of a small amplitude pumping potential no current is generated at zero temperature. At high temperature thermal agitation suppresses the pumping current. Thus the pumping current is maximal at some intermediate temperature. Our model describes therefore a pumping mechanism assisted by Brownian motion [1].
Spin transport in diluted magnetic semiconductor quantum wells
David Sanchez, in collaboration with researchers from the University of Madrid, and a collaborator from the University of Texas in Austin have analysed the spin dynamics in super-lattices containing magnetic impurities. Coulomb interaction, the negative differential conductance associated with resonant tunnelling and exchange interaction between the band spin electrons and the local moments provide for a rich behaviour of such systems.
Dynamical instability of electric field domains in ac-driven super-lattices
Rosa Lopez and David Sanchez, in collaboration with a researcher from the University of Madrid have provided a discussion of the stability of electric field domains in ac-driven super-lattices. For a THz signal it is found that it drives the system from a stationary current toward an oscillatory time dependence as the ac intensity increases. In the MHz regime, the current oscillates periodically reflecting an ac-induced motion and recycling of travelling domain walls.
General Situation
Since May of this year Rosa Lopez and David Sanchez are funded by this grant.
Other projects
M. Büttiker is also supported through a National Science Foundation grant for the investigation of 'Mesoscopic Physics, Electrical Transport and Non-equilibrium Statistical Mechanics'. M. Büttiker also participates in the NCCR on Materials with Novel Electronic Properties. Work carried out for these two projects will be reported separately.
References
[1] 'Noise-assisted classical adiabatic pumping in a symmetric periodic potential' O. Usmani, E Lutz and M. Büttiker, Phys. Rev. E66, 021111 (2002).
[2] 'Spin dynamics in diluted magnetic semiconductor super-lattices', Manuel Bejar, David Sanchez, Gloria Platero, and A.H. MacDonald, Phys. Rev. B (unpublished). cond-mat/0211557.
[3] Dynamical instability of electric field domains in ac driven super-lattices', Rosa Lopez (Geneva), David Sanchez, and Gloria Platero (unpublished).
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