Single Electron Tunneling through Quantum Dots:

Spin and Interaction Effects

Rolf J. Haug

Institut für Festkörperphysik,

Universität Hannover, Appelstr. 2, 30167 Hannover, Germany

Spin effects are currently discussed to have possible applications in quantum computing or spintronics concepts, but many details and parameters about spin dependent properties are unknown or poorly understood.

Single electron tunneling in high magnetic fields allows us to study the spin dependent electronic properties of semiconducting heterostructures in detail. For our experiments asymmetric double barrier tunneling structures were used. We studied tunneling through GaAs/AlAs heterostructures with InAs quantum dots embedded in the AlAs barriers. The presence of the dots is reflected in discrete steps in the I-V characteristics at finite bias voltages. The steps are due to resonant tunneling through quantized energy levels in individual InAs quantum dots [1,2]. Fluctuations in the tunneling current can be attributed to fluctuations in the local density of states of the emitter (see e.g. [3]).

In these systems we were able to study spin dependent tunneling. We measured the g-factors of the quantum dot states and found a pronounced anisotropy. In high magnetic fields when only the lowest Landau level in the 3d emitter remains occupied the current steps evolve into strongly enhanced peaks. These peaks are interpreted as resulting from a Fermi edge singularity, i.e. the interaction of the states in the leads with the charge on the quantum dot. A pronounced increase of the strength of the singularity is observed with increasing spin polarization for the tunneling with the majority spin [2].

[1] I. Hapke-Wurst, U. Zeitler, H.W. Schuhmacher, R.J. Haug, K. Pierz
and F.J. Ahlers, Semicond. Sci. Techn. **14**, L41 (1999).

[2] I. Hapke-Wurst, U. Zeitler, H. Frahm, A.G.M. Jansen, R.J. Haug
and K. Pierz, Phys. Rev. B **62**, 12621 (2000).

[3] T. Schmidt, P. König, E. McCann, V.I. Falko, and R.J. Haug,
Phys. Rev. Lett. **86**, 276 (2001).