This illustration shows how the rotational direction of the electromagnetic field depends on the direction the light travels along a silver nanowire. Image: TU Delft/Scixel.Spintronics in materials that are just a few atoms thick is an emerging field in which the 'spin' of electrons is used to process data, rather than the charge. Unfortunately, the spin only lasts for a very short time, making it (as yet) difficult to exploit in electronics.
Researchers from the Kavli Institute of Nanoscience at Delft University of Technology (TU Delft) in the Netherlands, working with the Netherlands Organisation for Scientific Research's AMOLF Institute, have now found a way to convert the spin information into a predictable light signal at room temperature. This discovery brings the worlds of spintronics and nanophotonics closer together and might lead to the development of an energy-efficient way of processing data, which could prove of us in data centres, for example. The researchers report their findings in a paper in Science.
The research involves a nano-construction consisting of two components: an extremely thin silver thread attached to a two-dimensional (2D) material called tungsten disulfide just four atoms thick. Using circularly polarized light, the researchers can create what are known as 'excitons' with a specific rotational direction, controlled by the rotational direction of the laser light, in the tungsten disulfide.
Excitons are actually electrons that have bounced out of their orbit. The laser beam ensures that the electrons are launched into a wider orbit around a positively charged 'hole', in much the same way a single electron orbits around a single proton in a hydrogen atom. The excitons thus created want to return to their original state. On their return to the smaller orbit, they emit energy in the form of light. This light contains information about the electron’s spin, but it is emitted in all directions.
To allow the spin information to be put to use, the Delft researchers returned to an earlier discovery. They had shown that when light moves along a nanowire, it is accompanied by a rotating electromagnetic field very close to the wire. This field spins clockwise on one side of the wire and anti-clockwise on the other side. When the light moves in the opposite direction, the spin directions change too. So the local rotational direction of the electromagnetic field depends on the direction the light travels along the wire.
“We use this phenomenon as a type of lock combination,” explains Kuipers. “An exciton with a particular rotational direction can only emit light along the thread if the two rotational directions correspond.”
Thus, a direct link is created between the spin information and the propagation direction of the light along the nanowire. It works almost perfectly: the spin information is 'launched' in the right direction along the thread in 90% of cases. In this way, fragile spin information can be carefully converted into a light signal and transported over far greater distances.
This technique, which works at room temperature, could lead to the development of new optoelectronic circuitry. “You don't need a stream of electrons, and no heat is released. This makes it a very low-energy way of transferring information,” says Kuipers.
The discovery also clears the way for combining the worlds of spintronics and nanophotonics. “This combination may well result in green information processing strategies at the nanoscale,” adds Kuipers.
This story is adapted from material from TU Delft, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.