Spin to charge conversion in the topological insulator HgTe and in STO-based two-dimensional electron gas

While classical spintronics has traditionally relied on ferromagnetic metals as spin generators and spin detectors, a new approach called spin-orbitronics exploits the interplay between charge and spin currents enabled by the spin-orbit coupling in non-magnetic systems, in particular using the spin Hall effect. However, the interconversion efficiency of the direct and inverse spin Hall effect is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronics.
In this contribution, we report the observation of spin-to-charge current conversion in strained mercury telluride, using spin pumping experiments at room temperature. We show high conversion rates due to the spin momentum locking property of HgTe surface states [1].

We then focus on the SrTiO₃ (STO)-based 2D electron system, presenting experiments performed on NiFe/Al/STO heterostructures. We investigate the nature of the spin-to-charge conversion through a combination of spin pumping, magnetotransport, spectroscopy and gating experiments, finding a very highly efficient spin-to-charge conversion. The conversion rate can be tuned in amplitude and rate by a gate voltage (cf. fig.1).
Finally, we harness the electric-field-induced ferroelectric-like state of SrTiO3 to manipulate the spin–orbit propertie of the two-dimensional electron gas, and efficiently convert spin currents into positive or negative charge currents, depending on the polarization direction [3]. This non-volatile effect opens the way to the electric-field control of spin currents and to ultralow-power spintronics, in which non-volatility would be provided by ferroelectricity rather than by ferromagnetism.

[1] P. Noel et al., Phys. Rev. Lett. 120, 167201 (2018)
[2] D. C. Vaz et al., Nature Materials 1-7 (2019)
[3] P. Noël et al., Nature, 580(7804), 483-486 (2020)