Spin Transport in Double Quantum Dots

Spin Blockade has been recently observed in transport experiments in semiconductor double quantum dots [1-4]. It occurs as a consequence of the Pauli exclusion principle and it produces the quenching of the tunneling current. Thus, these devices could behave as externally controllable spin-Coulomb rectifiers with potential applications in spintronics.
However, spin flip scattering induced by Hyperfine interaction gives rise to a finite current leakage which has been measured.
We have analyzed the electronic transport through a double quantum dot in dc magnetic fields in the regime where spin blockade occurs. Our model consists on rate equations for the electronic occupations and for the nuclei spin polarizations in the quantum dots in the presence of Hyperfine interaction. We discuss the current hysteretic behavior as a function of magnetic field, which is due to dynamical nuclear polarization induced by Hyperfine interaction [5].
Recent experiments of Electron Spin Resonance [6] show coherent spin rotations of a single electron in double quantum dots. Motivated by these experiments, we have analyzed as well the charge and spin dynamics in these systems under crossed ac and dc magnetic fields. The ac field produces coherent electron spin rotations within each quantum dot which compite with Rabi oscillations due to inter-dot tunnel, giving rise to a complicated time dependent behavior of the tunnelling current. We show that when the Zeeman splitting has the same value in both dots and spin flip is negligible, the electrons remain in the triplet subspace (dark subspace) performing coherent spin rotations and inter-dot tunnel Rabi oscillations and the current does not flow. This electronic trapping is removed either by finite spin relaxation or in the case where Zeeman splittings are different for each quantum dot [7].
Then, manipulating ac and dc magnetic fields electrons are driven to perform coherent spin rotations which can be detected by direct measurement of the tunneling current.


[1] K. Ono, et al., Science, 297, 1313 (2002).
[2] K. Ono et al., Phys. Rev. Lett., 92, 256803 (2004).
[3] A. Pfund et al., Phys. Rev. Lett., 99, 036801 (2007).
[4] F. H. L. Koppens et al., Science, 309, 1346 (2005).
[5] J. Iñarrea et al., Appl Phys. Lett.,91, 252112 (2007).
[6] F. H. L. Koppens et al., Nature, 442, 766 (2006).
[7] R. Sánchez et al., Phys. Rev. B, 77, 165312 (2008).