&Bullet; physics 14, p37

In a two-dimensional material, the orbital motion of electrons, and not their spin, is the dominant contribution to an effect used by spintronic devices.

Spintronic devices – those that use the spin of electrons instead of their charge – are based on effects that generate, control and recognize spin-polarized currents. Many of these schemes use the gemstone effect, in which an electrical current flowing through a material induces spin polarization. Recent studies have shown a weakness in most models of the gemstone effect: They neglect contributions from the orbital motion of an electron, since they are much smaller than those from the spin of an electron. However, calculations showed that these contributions in bulk solids and on metal surfaces can sometimes overshadow the spin contributions. Now a theory developed by Annika Johansson from the Physikalisches Institut in Halle (Germany) and colleagues shows that orbital contributions also dominate the gemstone effect in a two-dimensional metal oxide [1] .

Build a layered structure of a nanometer-thick oxide film deposited on a strontium titanate (STO) substrate, and a two-dimensional electron gas (2DEG) forms at the interface between the two materials. Previous studies have shown that this 2DEG has a number of promising properties for spintronics, including high mobility, tunable carrier density, huge spin-orbit coupling, and immunity to scattering. But in order to use STO in devices, researchers need a better understanding of the gemstone effect in these structures, and this is where the results of Johansson and her colleagues come into play.

The team examined the detailed band structure of the 2DEG at an STO interface. They found that the orbital contribution to the gemstone effect is more than ten times greater than the spin contribution. They say this great orbital gem effect could be used to demonstrate a recently proposed spintronic magnetoelectric device that could offer an energy efficient alternative to the traditional transistors used in electronics today.

Correction (April 1, 2021): In an earlier version, earlier calculations that suggest a dominant orbital contribution to the gemstone effect in bulk solids and on metal surfaces were not mentioned.

– Matteo Rini

Matteo Rini is the editor of physics.

## References

1. A. Johansson et al., “Spin and Orbital Gem Effects in a Two-Dimensional Electron Gas: Theory and Application to
${\text{SrTiO}}_{3}$

Interfaces “, Phys. Rev. research3, 013275 (2021).

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