After the plasmon-exciton hybrid device is excited with green laser light (green), coherent fluorescence occurs (red) due to the silver sawtooth nanoslit (right panel). The scale bar is 500nm. Image: Han and Ye, University of Groningen.Scientists at the University of Groningen in the Netherlands have used a silver sawtooth nanoslit array to produce valley-coherent photoluminescence in two-dimensional (2D) tungsten disulfide flakes at room temperature. Until now, this could only be achieved at very low temperatures.
Coherent light can be used to store or transfer information in quantum electronics. As such, the novel plasmon-exciton hybrid device created by the scientists is promising for use in integrated nanophotonics (light-based electronics). The scientists report their work in a paper in Nature Communications.
Tungsten disulfide has interesting electronic properties and is available as a 2D material. “The electronic structure of monolayer tungsten disulfide shows two sets of lowest energy points or valleys,” explains associate professor Justin Ye, head of the Device Physics of Complex Materials group at the University of Groningen.
One possible application for 2D tungsten disulfide is in photonics, as it can emit light with valley-dependent circular polarization, which offers a new way to store and manipulate digital information. But valleytronics requires coherent and polarized light, and previous work showed that the photoluminescence polarization in tungsten disulfide is almost random at room temperature.
“Tungsten disulfide is unique in that these two valleys are not identical,” explains Ye. This means that to create linearly polarized light via photoluminescence, both valleys must respond coherently. “But the intervalley scattering at room temperature largely destroys the coherence, so appreciable coherence is only achieved at very low temperatures that are close to zero.”
Ye and his postdoctoral researcher Chunrui Han (now working at the Institute of Microelectronics, Chinese Academy of Sciences) tried a different approach to creating linearly polarized light. This involved using a plasmonic metasurface, in the form of a silver sawtooth nanoslit array. The array interacts strongly with tungsten disulfide and can transfer the electromagnetic field induced by the light to the metal. “It enhances the light-material interaction,” says Ye.
By adding a thin layer of silver metasurface on top of a monolayer of tungsten disulfide, Ye and Han were able to increase the linear polarization induced by the valley coherence to around 27% at room temperature. “This room temperature performance is even better than the valley polarization obtained in many previous reports measured at very low temperatures,” says Ye.
They could further increase the linear polarization to 80% by adding the anisotropy of plasmonic resonance, in the form of the sawtooth pattern, to the optical response of the tungsten disulfide. This means that Ye and Han can now induce linearly polarized photoluminescence in 2D tungsten disulfide.
This accomplishment will make it possible to use both the valley coherence of tungsten disulfide and the plasmonic coherence of metasurfaces in optoelectronics at ambient temperatures. The next step is to replace the laser light that induced photoluminescence with an electrical input.
This story is adapted from material from the University of Groningen, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.