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# Electrostatic control over polarized currents through spinorbital Kondo effect

### George Martins (Oakland University)

#### 01.08.2012 at 10:15

In this talk, a brief introduction to pioneering results in quantum-dot-based spin filters will be presented,1–4 followed by our numerical results5 indicating that by suitably controlling the individual gate voltages of a capacitively coupled parallel double quantum dot [Fig. 1(a)], where each quantum dot is coupled to one of two independent non-magnetic channels, this system can be set into a spin-orbital Kondo state by applying a magnetic field. This Kondo regime, closely related to the SU(4) Kondo, flips total spin from one to zero through cotunneling processes [Fig. 1(b)] that generate almost totally spin-polarized currents with opposite spin orientation along the two channels [Fig. 2(a)]. Moreover, by appropriately changing the gate voltages of both quantum dots, one can simultaneously flip the spin polarization of the currents in each channel [Fig. 2(b)]. As a similar zero magnetic field Kondo effect has been recently observed by Y. Okazaki et al.,6 we analyze a range of magnetic field values where this polarization effect seems robust [Fig. 2(c,d)], suggesting that the setup may be used as an efficient bipolar spin filter, which can generate electrostatically reversible spatially separated spin currents with opposite polarizations.

Financial support by NSF under Grants No. DMR-0710529, 0955707, 1107994 is gratefully acknowledged.

1 P. Recher, E. V. Sukhorukov, and D. Loss, Phys. Rev. Lett. 85, 1962 (2000).

2 R. Hanson, L. M. K. Vandersypen, L. H. Willems van Beveren, J. M. Elzerman, I. T. Vink, and L. P. Kouwenhoven, Phys. Rev. B 70, 241304(R) (2004).

3 L. Borda, G. Zarand,W. Hofsteter, B. I. Halperin, and J. von Delft, Phys. Rev. Lett. 90, 026602 (2003).

4 D. Feinberg and P. Simon, Appl. Phys. Lett. 85, 1846 (2004).

5 C. A. B¨usser, A. E. Feiguin, and G. B. Martins, Phys. Rev. B 85, 241310(R) (2012).

6 Y. Okazaki, S. Sasaki, and K. Muraki, Phys. Rev. B 84, (R)161305 (2011).

7 S. Amasha, A. J. Keller, I. G. Rau, J. A. Katine, H. Shtrikman, and D. Goldhaber-Gordon, arXiv:1207.0526v1 [cond-mat.mes-hall].

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