Allgemeines Physikalisches Kolloquium im Wintersemester 2009/2010
Ort:    48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2,
Zeit:    Donnerstag, 14.01.2010 16:00 Uhr c.t.
Kolloquiums-Kaffee ab 15:45 Uhr vor dem Hörsaal

Controlling the spin of a single atom with non-equilibrium spin-polarized carrier
Prof. Dr. Joaquin Fernandez-Rossier, Departamento de Física Aplicada, Universidad de Alicante, Spanien

In this colloquium I will present two different systems that make it possible to control the spin orientation of a single Mn atom embedded in a nanostructure. In the first part of the talk I will consider a Mn atom placed on top of an insulating monolayer deposited on a metallic surface and under the influence of spin polarized current coming from a STM. I will show how depending on the direction of the current the spin of the Mn becomes polarized parallel or antiparallel to the STM magnetization. In addition, the relative orientation of the tip and the Mn spins affects the resistance of the system, which permits to map the spin dynamics into conductance.
The mechanism for spin exchange between the Mn spin and the transport quasiparticles [1] is able to account for existing inelastic STM experiments [2]. In the second part of the talk I will discuss the control of the spin of a single Mn atom as a single dopant in a CdTe quantum dot [3,4]. In this case, a circularly polarized laser field creates spin-polarized excitons in the dot which in turn interact with the Mn and result in its optical polarization. Two different strategies have been proposed, one with steady state pumping [5] and more recently with with ultrafast laser pulses [6]. In the talk I will show detailed simulations of the first strategy [7], and compare to recent experiments [8]. Finally, I will discuss the role played by the different spin relaxation mechanisms in this system and propose an new one, based on non-equilibrium phonons.

[1] J. Fernández-Rossier, Theory of single spin inelastic tunneling spectroscopy
Physical Review Letters 102, 256802 (2009)
[2] C. Hirjibehedin, et al., Large Magnetic Anisotropy of a Single Atomic Spin Embedded in
a Surface Molecular Network, Science 317, 1199 (2007)
[3] L. Besombes, et al.,Probing the Spin State of a Single Magnetic Ion in an Individual Quantum Dot Phys. Rev. Lett. 93, 207403 (2004)
[4] Y. Léger, L. Besombes, J. Fernández-Rossier, L. Maingault, and H. Mariette,
Electrical Control of a Single Mn atom in a Quantum Dot, Phys. Rev. Lett. 97, 107401, (2006)
[5] A. O. Govorov and A. V. Kalameitsev, Optical properties of a semiconductor quantum dot with a single magnetic impurity: photoinduced spin orientation, Phys. Rev. B 71, 035338 (2005)
[6] D. E. Reiter, T. Kuhn, and V. M. Axt, All-Optical Spin Manipulation of a Single Manganese Atom in a Quantum Dot, Phys. Rev. Lett. 102, 177403 (2009)
[7] C. L. Cao, L. Besombes, J. Fernández-Rossier, in preparation
[8] C. Le Gall, et al.,Optical Spin Orientation of a Single Manganese Atom in a Semiconductor Quantum Dot Using Quasiresonant Photoexcitation, Phys. Rev. Lett. 102, 127402 (2009)