Resonant optical control of the electrically induced spin polarization by periodic excitation

We show that the electron spin polarization generated by an electrical current may have its direction controlled and magnitude amplified by periodic optical excitation. The electrical and optical spin control methods were combined and implemented in a two-dimensional electron gas. By Kerr rotation in an external transverse magnetic field, we demonstrate unexpected long-lived coherent spin oscillations of the current-induced signal in a system with large spin-orbit interaction. Using a single linearly polarized pulse for spin manipulation and detection, we found a strong dependence on the pulse optical power and sample temperature indicating the relevance of the hole spin in the electron spin initialization. The signal was mapped in a Hall bar as function of the position relative to the injection contact. Finally, the presence of an in-plane spin polarization was directly verified by rotating the experimental geometry.

Figure 1

(a) Resonant spin amplification. (b) Optical detection of the CISP. (c) Optical control of the CISP. (d) Components of the spin polarization in (c). The Kerr rotation angle (${\varphi }_K$) is detected at the pump modulation frequency ($f_p$) or at the applied voltage frequency ($f_2$).

Figure 2

Electrical dependence of the CISP manipulation. (a) $B_{\mathrm{ext}}$ scans (scaled for clarity) of the KR signal for different applied voltages. (b) Detail of the normalized zero-field peak with a fitted Lorentzian curve for several voltages. (c) KR amplitude dependence on the external voltage.

Figure 3

Power dependence of the CISP control. (a) $B_{\mathrm{ext}}$ scans of the KR signal for different optical power. The curves were scaled for clarity. (b) Detail of the normalized data fit for different power. (c) KR amplitude and spin lifetime dependence for the zero-field peak.

Figure 4

CISP optical amplification dependence on (a) magnetic field, (b) temperature, and (c) position relative to the current source and drain contacts.

Figure 5

Dependence of the RSA pattern on $B_{\mathrm{in}}$ for the configuration: (a) $B_{\mathrm{ext}}\perp E$ and (b) $B_{\mathrm{ext}}\parallel E$. (c) Direct measurement of the in-plane spin polarization.