Observation of well-defined Kohn-anomaly in high-quality graphene devices at room temperature. (1st October 2022)

• Record Type: Journal Article
• Authors: Gadelha, Andreij C; Nadas, Rafael; Barbosa, Tiago C; Watanabe, Kenji; Taniguchi, Takashi; Campos, Leonardo C; Raschke, Markus B; Jorio, Ado
• Is Part Of: 2D materials. Volume 9:Number 4(2022)
• Publication Date: 2022-10-01
• Subjects: devices -- room temperature -- graphene -- photodoping -- Raman -- optoelectronics -- Kohn-anomaly; Graphene -- Periodicals; Materials science -- Periodicals; Nanostructured materials -- Periodicals; 620.115
• DOI: 10.1088/2053-1583/ac8e7f
• Languages: English
• ISSNs: 2053-1583

Abstract

Abstract: Due to its ultra-thin nature, the study of graphene quantum optoelectronics, like gate-dependent graphene Raman properties, is obscured by interactions with substrates and surroundings. For instance, the use of doped silicon with a capping thermal oxide layer limited the observation to low temperatures of a well-defined Kohn-anomaly behavior, related to the breakdown of the adiabatic Born–Oppenheimer approximation. Here, we design an optoelectronic device consisting of single-layer graphene electrically contacted with thin graphite leads, seated on an atomically flat hexagonal boron nitride substrate and gated with an ultra-thin gold layer. We show that this device is optically transparent, has no background optical peaks and photoluminescence from the device components, and no generation of laser-induced electrostatic doping (photodoping). This allows for room-temperature gate-dependent Raman spectroscopy effects that have only been observed at cryogenic temperatures so far, above all the Kohn-anomaly phonon energy normalization. The new device architecture, by decoupling graphene optoelectronic properties from the substrate effects, allows for observing quantum phenomena at room temperature.