Yasuhiro Tokura, NTT Research Laboratories

Spin-orbit interaction (SOI) in semiconductors provides a unique knob for electrical control of the spin qubits in quantum dots (QDs). In contrast to the effect of SOI on the flying spins, where an effective magnetic field appears in orthogonal to the electric field and its momentum, SOI affects localized spins in a QD in a different manner. Recently, we have systematically studied the SOI matrix elements of weakly coupled InAs QD depending on the direction of external magnetic field.[1] Noticing a magic-angle of the in-plane magnetic field where the SOI matrix element vanishes, we evaluate the symmetry of the relevant electronic states. For a QD strongly coupled to the leads, the splitting of the Kondo peak shows the amount of SOI. It is shown that the side gate voltage controls the SOI matrix element, which enables an efficient coherent control of spins by electric field.[2] Finally, the electron spin g-tensor is also shown to be controlled by the side gate, which suggests a possible realization of g-tensor magneto resonance (g-TMR),[3] which had only been demonstrated for ensemble spins in a quantum well.
In collaboration with S. Takahashi, R. S. Deacon, A. Oiwa and S. Tarucha, Dep. of Appl. Phys., Univ. of Tokyo.
References
[1] S. Takahashi, R. S. Deacon, K. Yoshida, A. Oiwa, K. Shibata, K. Hirakawa, Y. Tokura and S. Tarucha,
Phys. Rev. Lett. 104, 246801 (2010).
[2] Y. Kanai, R. S. Deacon, S. Takahashi, A. Oiwa, K. Yoshida, K. Shibata, K. Hirakawa, Y. Tokura, and
S. Tarucha, Nature Nanotechnology, 6, 511 (2011).
[3] R. S. Deacon, Y. Kanai, S. Takahashi, A. Oiwa, K. Yoshida, K. Shibata, K. Hirakawa, Y. Tokura and
S. Tarucha, Phys. Rev. B 84, 041302(R) (2011).