Scientists at the University of California at Berkeley and the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have exhibited a tunable graphene metamaterials-based tool kit for the long-wavelength terahertz light range.
Using the micro-scale device, the researchers demonstrated that graphene’s responsiveness to light at terahertz wavelengths can be tuned accurately. Research leader Feng Wang, who serves at Berkeley Lab's Materials Sciences Division as well as an assistant professor of physics at the University of California at Berkeley, stated that an array of graphene ribbons with a micro-scale width is the critical part of the equipment. The collective oscillations of the microribbons’ electrons can be monitored by altering the concentration of the charge carriers in them and changing the width of the ribbons, he said.
Graphene Ribbons and Plasmon Resonance
The concentration of graphene’s charge carriers can be augmented or lessened easily through the application of an intensified electric field called electrostatic doping. The collective oscillations of electrons are termed as plasmons. Wang stated that three-dimensional metal nanostructures demonstrate plasmons in high-frequency visible light. However, electrons in graphene shift in only two dimensions, as it has a merely one atom thickness, he said. Plasmons take place at relatively lower frequencies in two-dimensional systems, he added.
The researchers measured the terahertz light’s wavelength in hundreds of micrometers, while the width of the graphene ribbons utilized in the micro-scale device is merely1-4 µm. Wang said that a material whose structural dimensions are much smaller than the associated wavelength and whose optical properties are dissimilar to that of the bulk material is called a metamaterial.
The micro-scale device is a predecessor of the future instruments that can alter the intensity of the terahertz light and monitor the polarization and allow other electronic and optical components in two-dimensional applications from astronomy to medical imaging.
Wang concluded that his research team has not only studied plasmon coupling and light at terahertz wavelengths in graphene but also developed a prototype for upcoming graphene-based metamaterials at the terahertz range.