Researchers at Cornell University describe the ability to use graphene as a mediator between vibrational modes, allowing for direct energy transfer from one frequency to another. The team designed graphene “drums” with diameters ranging from 5 to 20 micrometers. Those drums can be set in motion either by an alternating electric field or by the random thermal vibrations of their constituent atoms (the same atomic vibrations that define an object’s temperature); the movement is detected through laser interferometry, a method devised several years ago at Cornell.
External voltage applied to the graphene membrane acts as a sort of “tuning peg” to control the membrane tension and engineer the coupling needed to control one oscillation mode by exciting the other. The team explains that it has shown that there is an effect that will convert energy from one mechanical mode to another mechanical mode. That allows to either damp out or amplify vibrations of one mode by activating the other mode, with an ability to change the fundamental frequency of this object’s motion.
The term “phonon cavity” was chosen, because the mechanical effect is similar to that of an optical cavity, which can be used to convert energy from laser light into mechanical motion. Phonons are quasi-particles used to describe vibrations in the same way that photons are particles of light. This discovery may pave the way for the application of graphene mechanical resonators in telecommunication applications – for instance, as frequency mixers.
In addition, when cooled to near absolute zero, these resonators can play a key role in detection of the faintest quantum signals and in identifying and developing new, secure telecommunication technologies.