Acoustic terahertz graphene plasmons revealed by photocurrent nanoscopy

Alonso-Gonz�lez, Pablo; Nikitin, Alexey Y.; Gao, Yuanda; Woessner, Achim; Lundeberg, Mark B.; Principi, Alessandro; Forcellini, Nicol�; Yan, Wenjing; V�lez, Sa�l; Huber, Andreas. J.; Watanabe, Kenji; Taniguchi, Takashi; Casanova, F�lix; Hueso, Luis E.; Polini, Marco; Hone, James; Koppens, Frank H. L.; Hillenbrand, Rainer

Abstract

© 2017 Macmillan Publishers Limited, part of Springer Nature. Terahertz (THz) fields are widely used for sensing, communication and quality control. In future applications, they could be efficiently confined, enhanced and manipulated well below the classical diffraction limit through the excitation of graphene plasmons (GPs). These possibilities emerge from the strongly reduced GP wavelength, λ p, compared with the photon wavelength, λ 0, which can be controlled by modulating the carrier density of graphene via electrical gating. Recently, GPs in a graphene/insulator/metal configuration have been predicted to exhibit a linear dispersion (thus called acoustic plasmons) and a further reduced wavelength, implying an improved field confinement, analogous to plasmons in two-dimensional electron gases (2DEGs) near conductive substrates. Although infrared GPs have been visualized by scattering-type scanning near-field optical microscopy (s-SNOM), the real-space imaging of strongly confined THz plasmons in graphene and 2DEGs has been elusive so far - only GPs with nearly free-space wavelengths have been observed. Here we demonstrate real-space imaging of acoustic THz plasmons in a graphene photodetector with split-gate architecture. To that end, we introduce nanoscale-resolved THz photocurrent near-field microscopy, where near-field excited GPs are detected thermoelectrically rather than optically. This on-chip detection simplifies GP imaging as sophisticated s-SNOM detection schemes can be avoided. The photocurrent images reveal strongly reduced GP wavelengths (λ p ≈ λ 0 /66), a linear dispersion resulting from the coupling of GPs with the metal gate below the graphene, and that plasmon damping at positive carrier densities is dominated by Coulomb impurity scattering.

Citation

Alonso-González, P., Nikitin, A. Y., Gao, Y., Woessner, A., Lundeberg, M. B., Principi, A., …Hillenbrand, R. (2017). Acoustic terahertz graphene plasmons revealed by photocurrent nanoscopy. Nature Nanotechnology, 12(1), 31-35. https://doi.org/10.1038/nnano.2016.185

• Journal Article Type: Article
• Acceptance Date: Aug 23, 2016
• Online Publication Date: Oct 24, 2016
• Publication Date: 2017-01
• Deposit Date: Nov 14, 2019
• Journal: Nature Nanotechnology
• Print ISSN: 1748-3387
• Electronic ISSN: 1748-3395
• Publisher: Nature Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 12
• Issue: 1
• Pages: 31-35
• DOI: https://doi.org/10.1038/nnano.2016.185
• Keywords: Electrical and Electronic Engineering; General Materials Science; Atomic and Molecular Physics, and Optics; Bioengineering; Condensed Matter Physics; Biomedical Engineering
• Public URL: https://nottingham-repository.worktribe.com/output/3084590
• Publisher URL: https://www.nature.com/articles/nnano.2016.185
• Additional Information: Received: 13 January 2016; Accepted: 23 August 2016; First Online: 24 October 2016; : R.H. is a co-founder of Neaspec GmbH, a company producing scattering-type scanning near-field optical microscope systems such as the one used in this study. All other authors declare no competing financial interests.