Spin-orbit interaction in semiconductors

Spin-orbit interaction can be observed as a coherent spin precession of moving electron spins. Using optical pump-probe measurements, the spin precession frequency has been measured as a function of the electron’s velocity in semiconductor quantum-well structures. The velocity is controlled by a current that flows through lateral electrical contacts. In this way, the size and symmetry of the spin-orbit interaction can be determined for a wide range of semiconductor materials [1].

We have recently established an all-optical method to determine spin-orbit interaction where no electrical contacts and no lithographical patterning of the semiconductor is needed. A diffusive spin current is induced by exciting spin polarization with an optical pump pulse. By mapping the dependence of the spin precession frequency on the spatial position relative to the pump pulse, a precise measurement of spin-orbit interaction is made possible [2].

Typically, the energy of the spin-orbit interaction (Rashba and Dresselhaus) scales linearly with electron momentum. However, there is also a contribution that depends on the cube of the momentum. This leads to additional spin dephasing, but also allows us to control the precession phase of an electron by an electrical current [3]. This is relevant for applications and enables a direct determination of the cubic Dresselhaus interaction.


Publications

[1] L. Meier, G. Salis, I. Shorubalko, E. Gini, S. Schön and K. Ensslin, “Measurement of Rashba and Dresselhaus spin-orbit magnetic fields,” Nature Phys. 3, 650 (2007).

[2] M. Kohda, P. Altmann, D. Schuh, S. D. Ganichev, W. Wegscheider and G. Salis, “All-optical evaluation of spin-orbit interaction based on diffusive spin motion,” Appl. Phys. Lett. 107, 172402 (2015).

[3] P. Altmann, F. G. G. Hernandez, G. J. Ferreira, M. Kohda, C. Reichl, W. Wegscheider and G. Salis, “Current-Controlled Spin Precession of Quasistationary Electrons in a Cubic Spin-Orbit Field,” Phys. Rev. Lett. 116, 196802 (2016).

Spin polarization

(a, b) Spin polarization as a function of position y and time t drifts in an applied electric field (dashed violet lines). The precession phase of the helical mode pattern shifts with time (green lines).
(c,d) The phase is characterized by a wave number q and a precession frequency w. The precession frequency depends linearly on the drift velocity with a slope that is characterized by cubic Dresselhaus spin-orbit interaction. For more details, see [3].