Irradiating a quantum ring to regulate spin-dependent transport of electrons

Spin-current generation and manipulation are intrinsic to spintronics, technologies that exploit both electron spin and charge for ultrafast computing applications.

Using ferromagnetic electrodes is the most common generation method. Spin direction control is conducted either by applying a magnetic field or tuning spin-orbit coupling to manipulate the degree of spin polarization. Still, poor current intensity and high magnetic flux hamper advances.

To address these challenges, Sudin Ganguly and Santanu K. Maiti explore an approach where they regulate the spin-dependent transport externally by irradiating a quantum ring that bridges the contact electrodes in a two-terminals bridge system. The theoretical approach is based on time-periodic fields produced by light that can dynamically control material and topological properties.

For their hexagonal-shaped conducting quantum ring, the researchers assumed a diameter of about 0.2 nanometer, roughly the size of a benzene molecule, which has served as a good model for charge transport and spin polarization through single molecule junctions.

When the ring is irradiated, electron hopping between pairs of atoms can be tailored to a high degree to significantly influence the probability that the electron spin will be up or down.

Based on the assumption the energy of the incident light must be greater than four times the hopping strength, the researchers used near-ultraviolet/extreme ultraviolet regime. They also considered a much bigger ring, with 40 lattice sites, and found almost 100% spin polarization.

“Our analysis can be generalized to any other loop conductors and interferometric geometries as well, and our findings may provide a boost in the field of spintronics at the nanoscale level,” Ganguly said. “We strongly believe our proposal can be examined experimentally in a suitable laboratory.”

Source: “Selective spin transmission through a driven quantum system: A new prescription,” by Sudin Ganguly and Santanu K. Maiti, Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0045566 .