MOdulating Spin currents with Electrically driven Spin accumulation

Brief description of the proposal

The manipulation of spin currents for information and communication technologies is the goal of spintronics, as much as controlling charge currents is the key ingredient of electronics. However, the control of spin currents with external stimuli has insofar proven elusive. At variance with the electrical charge, spin is not a conserved physical quantity in solids and, furthermore, it weakly interacts with externally applied fields. Moreover, spin injection in solids is an inefficient process. In classical spintronic devices, spin-polarized currents are obtained by leveraging on the exchange interaction between conduction electron spins and magnetic materials. An innovative approach (spin-orbitronics) exploits instead the Spin-Orbit Coupling (SOC) in nonmagnetic materials to generate, detect, or exploit spin-polarized currents.

Positioning itself at the cutting edge of spin-orbitronics, the MOSES project aims at developing innovative spintronic devices using materials (Si, Ge, and SiGe) and manufacturing processes fully compatible with the mainstream silicon technology, in which SOC could be exploited for the efficient generation, detection, and manipulation of spin currents.

MOSES relies on a nonlocal spin-injection/spin-detection scheme established by the PI’s unit, where a very efficient spin injection is achieved at the source electrode through optical orientation, a phenomenon consisting in the SOC-mediated transfer of angular momentum from circularly polarized light to the photoexcited conduction electrons. The SOC-mediated spin-to-charge conversion, known as the inverse spin-Hall effect, is used for spin detection. Recently, we demonstrated that such approach can induce a sizeable spin voltage, the spin counterpart of an electrostatic voltage, at distances of few µm, compatible with multiterminal spintronic devices. MOSES will expand the functionality of the demonstrated spin injection/detection scheme by adding the electric modulation of spin currents. In our very recent work, we investigated a route to the spin-current modulation. We propose to selectively control the spin-voltage for currents carrying opposite spin by exploiting the spin accumulation resulting from the SOC-induced charge-to-spin conversion (spin-Hall effect, SHE). SHE is obtained by a charge current flowing in a nm-thick heavy-metal film in proximity of the channel where the spin current is confined. Preliminary work suggests that a detectable spin current modulation is possible. MOSES will thus investigate the device geometry and materials to boost such spin-by-spin modulation.

Adding such a functionality to our platform is clearly a high risk-high gain task that, on one hand, would unveil extremely promising possibilities for applications in the field of spin devices and on the other hand will enable us to investigate the fundamental laws of spin transport in the presence of external stimuli.