Scientists from University of Regensburg, Massachusetts Institute of Technology, Moscow institute of Physics and Technology, and University of Kansas have discovered abnormally strong light absorption in graphene. The effect arises from the conversion of ordinary electromagnetic waves into super-slow surface waves running through graphene. The observation is of fundamental interest and shows in an impressive way how the interaction of Bernstein modes, collective excitations of electrons driven by their cyclotron motion and the smearing of electric fields at the smallest scales due to nonlocality can influence the radiation absorption of graphene. This behavior could serve as the basis for extremely sensitive infrared and terahertz detectors much smaller than existing ones, with similar absorption efficiency. The investigations were carried out in the framework of the Collaborative Research Centre 1277 and published in the journal Nature Physics.
Frozen light in graphene. Credit: Darya Sokol Everyday experience teaches us that the efficiency of light energy harvesting is proportional to the absorber area. The solar panel "fields" that dot many deserts are a clear indication of this. Can an object absorb radiation from an area larger than itself? It turns out yes, and it is possible when the frequency of light is in resonance with the movement of electrons in the absorber. In this case the absorption area of the radiation is on the order of the square of the wavelength of the light, although the absorber itself can be extremely small. In order to receive electromagnetic waves—from radio frequencies to the ultraviolet range—with the lowest possible losses, resonant absorption phenomena are used. Two classes of resonances are particularly promising for these applications: the first and most fundamental is called the cyclotron resonance and occurs when the frequency of the incoming electromagnetic wave matches the frequency at which the electron spins in a circular path in an applied magnetic field. The second resonance results from the synchronous movement of electrons and the electromagnetic field from one sample boundary to the other and is called plasmon resonance. Both resonances have been successfully investigated experimentally in different systems. However, the observed effect of absorption enhancement has been comparatively small in most of the semiconductors studied so far. The sketch of the studied sample. Graphene in perpendicular magnetic field B is illuminated by terahertz radiation. Multiple metal contacts (yellow) are used for read-out of the photosignal. Credit: Denis A. Bandurin In the present work,…