Generation and Detection of Spin Currents in Semiconductor Nanostructures with Strong Spin-Orbit Interaction

Storing, transmitting, and manipulating information using the electron spin resides at the heart of spintronics. Fundamental for future spintronics applications is the ability to control spin currents in solid state systems. Among the different platforms proposed so far, semiconductors with strong spin-orbit interaction are especially attractive as they promise fast and scalable spin control with all-electrical protocols. Here we demonstrate both the generation and measurement of pure spin currents in semiconductor nanostructures. Generation is purely electrical and mediated by the spin dynamics in materials with a strong spin-orbit field. Measurement is accomplished using a spin-to-charge conversion technique, based on the magnetic field symmetry of easily measurable electrical quantities. Calibrating the spin-to-charge conversion via the conductance of a quantum point contact, we quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of 34%.

Figure 1

(a) Schematic of the system used to generate spin currents. Charge currents are depicted as black lines, spin currents are depicted as red and blue lines. (b) Energy dependent, spin sensitive, transmission probability of ${\mathrm{QPC}}_3$. At zero field the transmission is tuned to $1/2$. A positive (negative) field suppresses (enhances) the transmission probability of one spin eigenstate. (c) Representation of spin and charge currents in ${\mathrm{QPC}}_3$ as a function of magnetic field. The net charge current in ${\mathrm{QPC}}_3$ varies with the magnetic field.

Figure 2

(a) Atomic force micrograph of our sample, where dark lines indicate insulating trenches. The frame size is $5\times 5\mu {\mathrm{m}}^2$. (b) ${\mathrm{QPC}}_3$ conductance as a function of the voltage applied to $g_4$ and $g_5$, for different values of magnetic field. (c) Cavity four-terminal resistance as a function of the voltage applied to $g_4$ and $g_5$ and magnetic field. (d) Line cut of (c) along the dashed line for different temperatures. (e) $V_3/I$ as a function of the voltage applied to $g_4$ and $g_5$ and magnetic field. (f) Line cut of (e) along the dashed line for different temperatures.

Figure 3

(a)–(d) Comparison between ${\partial }_B{V}_3/I$ (markers) and ${\partial }_V{G}_3/G_3$ (solid line) as a function of the side gate voltage for a different number of modes in ${\mathrm{QPC}}_1$ and ${\mathrm{QPC}}_2$, as indicated in each subfigure. Dots and squares in (a) represent two identical measurements performed in different cooldowns [22].

Figure 4

(a) Comparison between ${\partial }_B{V}_2/I$ acquired with two different cavity shapes (dots and squares) both having $N_1=N_3=4$ and ${\partial }_V{G}_2/G_2$ (solid line) as a function of the voltage applied to $g_3$. The electrical setup was modified to use ${\mathrm{QPC}}_2$ as detector. (b), (c), and (d) as in Fig. 3 but with the magnetic field aligned perpendicularly to ${\mathrm{QPC}}_3$.