Non-volatile spin-charge conversion with “ferroelectric” two-dimension electron gases

A promising approach for beyond CMOS electronics is spintronics, which relies on ferromagnets to provide non-volatility and to generate and detect spin currents. Despite its numerous advantages, spintronics still requires the application of intense electrical currents for magnetization switching. This has been driving research on multiferroics for over a decade, with a view to achieve low-power electric-field control of magnetization. However, practical materials are scarce and magnetoelectric switching remains difficult to control. In a recent paper published in Nature, we demonstrate an alternative strategy to achieve low-power spin detection, in a non-magnetic system. We harnessed the electric-field-induced ferroelectric-like state of SrTiO3 to manipulate the spin–orbit properties of a two-dimensional electron gas – 2DEG (formed by depositing a few Å of Al onto SrTiO3). This led to the efficient conversion of spin currents into positive or negative charge currents, depending on the ferroelectric polarization direction. 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.
In another article just out in Phys. Rev. Materials, we also showed that a 2DEG could be formed by depositing Al onto Ca-substituted SrTiO3 (here Ca stabilizes the material into a ferroelectric ground state). The 2DEG showed signatures of a ferroelectric transition in its transport properties and its resistance shows a hysteretic dependence on electric field as a consequence of ferroelectricity.
With these two papers, we propose a new approach to bridge ferroelectricity and spintronics beyond magnetoelectricity and multiferroics, as envisioned in the ERC Advanced Grant FRESCO funding this research.

The work published in Nature was performed in collaboration with Spintec and that published in Phys. Rev. Mater. in collaboration with Spintec, the MPQ lab from Université de Paris and the SPMS lab of Centrale/Supélec.

Non-volatile electric control of spin–charge conversion in a SrTiO3 Rashba system
Paul Noël, Felix Trier, Luis M. Vicente Arche, Julien Bréhin, Diogo C. Vaz, Vincent Garcia, Stéphane Fusil, Agnès Barthélémy, Laurent Vila, Manuel Bibes & Jean-Philippe Attané
Nature, 580, 483 (2020)

See also the News and Views by S. Gariglio, the press release by CNRS, the article in Le Monde and the perspective in Physics World.

Switchable two-dimensional electron gas based on ferroelectric Ca:SrTiO3
Julien Bréhin, Felix Trier, Luis M. Vicente-Arche, Pierre Hemme, Paul Noël, Maxen Cosset-Chéneau, Jean-Philippe Attané, Laurent Vila, Anke Sander, Yann Gallais, Alain Sacuto, Brahim Dkhil, Vincent Garcia, Stéphane Fusil, Agnès Barthélémy, Maximilien Cazayous, and Manuel Bibes
Phys. Rev. Mater. 4, 041002(R) (2020)

See also the Synopsis in Physics.