Resonant Terahertz Detection Using Graphene Plasmons

Plasmons, collective oscillations of electron systems, can efficiently couple light and electric current, and thus can be used to create sub-wavelength photodetectors, radiation mixers, and on-chip spectrometers. Despite considerable effort, it has proven challenging to implement plasmonic devices operating at terahertz frequencies. The material capable to meet this challenge is graphene as it supports long-lived electrically-tunable plasmons. Here we demonstrate plasmon-assisted resonant detection of terahertz radiation by antenna-coupled graphene transistors that act as both plasmonic Fabry-Perot cavities and rectifying elements. By varying the plasmon velocity using gate voltage, we tune our detectors between multiple resonant modes and exploit this functionality to measure plasmon wavelength and lifetime in bilayer graphene as well as to probe collective modes in its moir\'e minibands. Our devices offer a convenient tool for further plasmonic research that is often exceedingly difficult under non-ambient conditions (e.g. cryogenic temperatures and strong magnetic fields) and promise a viable route for various photonic applications.Comment: 19 pages, 12 figure

Terahertz photomixing spectroscopy of two-dimensional semiconductor plasmons

This thesis reports the findings of terahertz photomixer spectroscopy performed on plasmonic grating-gate detectors made from high mobility two-dimensional electron gas (2DEG) material. In recent years, these detectors have seen significant improvements in sensitivity and currently exhibit a noise equivalent power of 10^-8 W/sqrt(Hz) However, further improvements are essential for these detectors to become truly useful; the ultimate goal being a NEP \u3c 10^-10 W/sqrt(Hz) To this end, it is necessary to understand the physical properties of the mechanism underlying the detectors photoresponse, namely plasmons. Although two-dimensional plasmons were first observed in semiconductors in 1978, to date, their physical properties, for example scattering and absorption cross section, are relatively unknown. The primary purpose of this work is to develop a measurement system capable of revealing these properties and utilize this system to understand the absorption of radiation by two-dimensional plasmons. By no means will the study of plasmonic properties using this system end when this work is completed. Rather, this work lays the foundation for years of future research in this field