Scanning electron microscope image of the chimney-shaped nanopillars used as a spin-light interface. Credit: (Shula Chen, Creative Commons Attribution 4.0 International License)A new device concept able to efficiently transfer the information carried by electron spin to light at room temperature has been devised by scientists at Linköping University and the Royal Institute of Technology in Sweden. The concept, which is based on nanoscale chimney-shaped pillars where light can be guided easily and more efficiently coupled in and out, could help new information technology and future spin–photonic applications.
There is much in research being carried out into developing faster, smaller and more energy-efficient information technology based around the spin and the charge of electrons, a field known as “spintronics”. The direction of electron spin carries encoded information that could theoretically be converted into light that can transfer the information through optic fibres. This transfer of quantum information could lead to technology that exploits electron spin and light and their interaction: “opto-spintronics”.
Opto-spintronics uses the principle that an electron’s spin state is what determines the properties of the emitted chiral light, light where the electric field rotates in one direction when seen in the direction of travel of the light, with rotation being determined by the direction of the electron’s spin. Electrons can easily lose their spin orientations as temperature rises, so efficient quantum information transfer at room temperature is crucial. However, at room temperature the electron spin orientation is nearly randomized, with the encoded information either lost or too vague for reliable conversion.
“It paves the way for a new design of spin-light interfaces that bridge between the electron spin and chiral light – the two main media for information processing and communications. It provides a building block for future quantum information technology based on polarized spin and light.”Weimin Chen
The aim for this study, published in Nature Communications [Chen et al. Nat. Commun (2018) DOI: 10.1038/s41467-018-06035-1], was to examine if spin-filtering remains effective in 1D semiconductor nanostructures, viewed as building blocks for nano-photonics, and also to explore such 1D nanostructures as a spin–photon interface at room temperature. The new interface was found to enhance the electron spin signals at room temperature, and also convert these spin signals to corresponding chiral light signals moving in a particular direction.
The proposed device – using very small stacked disks of gallium nitrogen arsenide a couple of nanometres high with a thin film of gallium arsenide between to form them into nanopillars – could improve spin signals because of the minimal defects of the material. As lead researcher Weimin Chen told Materials Today, “It paves the way for a new design of spin-light interfaces that bridge between the electron spin and chiral light – the two main media for information processing and communications. It provides a building block for future quantum information technology based on polarized spin and light.”
The study demonstrates that the defect-engineered spin filtering is efficient even in nanostructures, making the approach viable for future nanoscale spintronics and opto-spintronics. The team are now looking to further improve the efficiency of polarized spin-light conversion by optimizing the structural designs, and to integrate it with other spintronic building blocks for multifunctional devices.