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Modulation of THz Metamaterials Using Graphene Surface Plasmons

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If you have a question about this talk, please contact Teri Bartlett.

The THz portion of the electromagnetic spectrum bridges the gap between electronic and optical devices and provides a wealth of opportunity for technological exploitation in areas such as free space communication, security, bio-sensing and trace gas detection. Metamaterials provide a powerful tool for the manipulation of THz radiation, but the tunability required for active control is difficult to achieve in predominantly metal based devices. Plasmonics, on the other hand, offers the capability to confine light in subwavelength dimensions and in graphene, the ability to electrostatically control the charge density predicates tuneable and switchable devices.

In this talk, I will first introduce graphene plasmonics and demonstrate how the absorption resonances of graphene ribbons can be tuned dimensionally and with electrostatic gating. The importance of the substrate is then highlighted with experiments which show the coupling of the plasmonic resonances to surface phonons in the underlying silicon dioxide [1].

I will then move on to discuss hybrid metamaterials consisting of graphene plasmonic resonators, coupled to conventional split ring resonators [2]. With electrostatic gating of the graphene, up to 60% modulation of the transmission is achieved and the interaction of the two resonances reaches the strong coupling regime. Two peaks are observed in the transmission spectra, which exhibit a typical anti-crossing and exchange of oscillator strength. Numerical simulations provide an insight to the coupled system and reproduce well the experimental observations and reveal highly confined bonding and anti-bonding modes, which may find applications in chemical and/or biological sensing. Such hybrid metamaterials can be employed as switches and modulators, and provide a platform for exploring cavity-enhanced optical processes in graphene plasmonic structures for applications including sensing, photo-detection and nonlinear frequency generation.

[1] I. J. Luxmoore, C. H. Gan, P. Q. Liu, F. Valmorra, P. Li, J. Faist and G. R. Nash, ACS Photonics 1, 1151 (2014). [2] P. Q. Liu, I. J. Luxmoore, S. A. Mikhailov, S. A. Savostianova, F. Valmorra, J. Faist and G.R. Nash, arXiv 1501.05490 (2015).

This talk is part of the Semiconductor Physics Group Seminars series.

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