Scientists have generated circularly polarized light and controlled its
direction without using clunky magnets or very low temperatures. The
findings, by Nagoya University researchers and colleagues in Japan, and
published in the journal Advanced Materials, show promise for the
development of materials and device methods that can be used in optical
quantum information processing.
Light particles called photons have interesting properties that can be
exploited for storing and transporting data, and show tremendous promise for
use in quantum computing.
For this to happen, information is first stored in electrons that then
interact with matter to generate data-carrying photons. Information can be
encoded in the direction of an electron's spin, just as it is stored in the
form of 0 and 1 in the 'bits' of computers . Data can also be stored when
electrons occupy 'valleys' found in the energy bands they move between while
they orbit an atom. When these electrons interact with specific
light-emitting materials, they generate twisting 'chiral' 'valley-polarized
light,' which shows potential for storing large amounts of data.
So far, however, scientists have only managed to generate this type of
circularly polarized light using magnets and very cold temperatures, making
the technique impractical for widespread use.
Nagoya University applied physicists Taishi Takenobu and Jiang Pu led a team
of scientists to develop a room-temperature, electrically controlled
approach for generating this chiral valley-polarized light.
First, they grew a monolayer of semiconducting tungsten disulfide on a
sapphire substrate and covered it with an ion-gel film. Electrodes were
placed on either end of the device and a small voltage was applied. This
generated an electric field and ultimately produced light. The team found
that chiral light was observed between -193 degrees Celsius and room
temperature from the portions of the device where the sapphire substrate was
naturally strained as a result of the synthetic process. It could only be
generated from the strain-free areas, however, at much colder temperatures.
The scientists concluded that strain played a crucial role in generating
room temperature valley-polarized light.
They then manufactured a bending stage on which they placed a tungsten
disulfide device on a plastic substrate. They used the bending stage to
apply strain to their material, driving an electric current in the same
direction of the strain and generating valley-polarized light at room
temperature. Applying an electric field to the material switched the chiral
light from moving in one direction to moving in the other.
"Our use of strained monolayer semiconductors is the first demonstration of
a light-emitting device that can electrically generate and switch right- and
left-handed circularly polarized light at room temperature," says Takenobu.
The team will next further optimize their device with the aim of developing
practical chiral light sources.
Reference:
Jiang Pu et al, Room‐Temperature Chiral Light‐Emitting Diode Based on
Strained Monolayer Semiconductors, Advanced Materials (2021).
DOI: 10.1002/adma.202100601
Tags:
Physics