Graphene Nano-Optics in the Terahertz Gap

Author(s)

Feres, Flavio H. ; Barcelos, Ingrid D. ; Cadore, Alisson R. ; Wehmeier, Lukas ; Noerenberg, Tobias ; Mayer, Rafael A. ; Freitas, Raul O. ; Eng, Lukas M. ; Kehr, Susanne C. ; Maia, Francisco C. B.

• Document type: Journal article
• Source: Nano Letters; v. 23, n. 9, p. 8-pg., 2023-05-01.

Abstract

Graphene nano-optics at terahertz (THz) frequencies (nu) is theoretically anticipated to feature extraordinary effects. However, interrogating such phenomena is nontrivial, since the atomically thin graphene dimensionally mismatches the THz radiation wavelength reaching hundreds of micrometers. Greater challenges happen in the THz gap (0.1-10 THz) wherein light sources are scarce. To surpass these barriers, we use a nanoscope illuminated by a highly brilliant and tunable free-electron laser to image the graphene nano-optical response from 1.5 to 6.0 THz. For nu < 2 THz, we observe a metal-like behavior of graphene, which screens optical fields akin to noble metals, since this excitation range approaches its charge relaxation frequency. At 3.8 THz, plasmonic resonances cause a field-enhancement effect (FEE) that improves the graphene imaging power. Moreover, we show that the metallic behavior and the FEE are tunable upon electrical doping, thus providing further control of these graphene nano-optical properties in the THz gap. (AU)

• FAPESP's process: 22/11987-0 - Multi-user equipment approved in grant 2019/14017-9: custom s-SNOM nanoscope optimized for operation with IR-THZ synchrotron
• Grantee: Raul de Oliveira Freitas
• Support Opportunities: Multi-user Equipment Program
• FAPESP's process: 22/02901-4 - Nano-optics of polaritons in two-dimensional crystals and at the metal/dielectric interface in the mid-to-far infrared
• Grantee: Francisco Carlos Barbosa Maia
• Support Opportunities: Research Grants - Initial Project
• FAPESP's process: 19/14017-9 - From excitons waves to THz-phonons: 2Ds materials nano-optics via synchrotron infrared nanospectroscopy
• Grantee: Raul de Oliveira Freitas
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 21/10487-0 - Multi-user equipment approved in grant 2019/14017-9: mid-IR-VIS illumination units for synchrotron s-SNOM
• Grantee: Raul de Oliveira Freitas
• Support Opportunities: Multi-user Equipment Program