Coupling light into graphene plasmons through surface acoustic waves

Researchers at the CIE Moncloa Campus have proposed a novel scheme for coupling laser light into graphene plasmons with the help of electrically generated surface acoustic waves (SAWs).

09/01/2014

Researchers at the Moncloa Campus within the Materials for the Future Cluster have proposed a novel scheme for coupling laser light into graphene plasmons with the help of electrically generated surface acoustic waves (SAWs).

Plasmons are electromagnetic waves confined to the interface between two materials and accompanied by collective oscillations of surface charges. The strong spatial confinement of the electromagnetic field and its coupling to charge carriers allow for the manipulation of light at subwavelength scales (beyond the diffraction limit of classical optics), opening the possibility to integrate electronics and optics at the nanoscale. Further promising plasmonic applications include single molecule detection, metamaterials, and light harvesting.

Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, forms a pure two-dimensional electron gas that supports plasmons in a broad frequency range from the midinfrared to the terahertz domain. Unlike conventional plasmons in noble metals, graphene plasmons can be tuned in situ through the modulation of the carrier density by electrostatic gating. However, in the experiments realized so far, graphene plasmon laser coupling required either complex near-field techniques or the patterning of micro- or nanoscale arrays for far-field coupling, where edge scattering reduces the plasmon lifetime, hindering the potential of the graphene plasmonic applications.

In the novel scheme proposed at the Moncloa Campus, far-field radiation is converted into graphene plasmons by deforming the graphene sheet with a SAW and thus forming a tunable optical grating without the need of any patterning. A interdigital transducer (IDT) on a piezoelectric film is used to launch the SAW across the graphene sheet, as shown in the figure. By diffraction at the grating, incident laser light can overcome the momentum mismatch and excite plasmons in the graphene sheet. Moreover, plasmons can be switched electrically, via the high frequency signal at the IDT, whereas the plasmon resonance can be tuned via electrostatic gating. In addition, the IDT technology allows for many different plasmon functionalities. For example, curved IDTs can create interfering SAWs for plasmon focusing. Thus, SAWs offer the possibility to tailor electrically switchable graphene-based metamaterials.

This work has been led by Jürgen Schiefele (Departamento de Física de Materiales, UCM) and Jorge Pedrós (Instituto de Sistemas Optoelectrónicos y Microtecnología, UPM), together with Fernando Sols (UCM), Fernando Calle (UPM) and Francisco Guinea (CSIC). Support from the Marie Curie ITN NanoCTM, the Campus de Excelencia Internacional (Campus Moncloa UCM-UPM), ERC Advanced Grant No. 290846, and MICINN Grants No. FIS2008-00124, FIS2010-21372, TEC2010-19511, and FIS2011-23713 is acknowledged.

Tag: Materials for the Future    Source: CEI Campus Moncloa

Event date:

09/01/2014