Observation of well-defined Kohn-anomaly in high-quality graphene devices at room temperature

TL;DR

This study demonstrates a novel graphene device architecture enabling room-temperature observation of a well-defined Kohn-anomaly, previously only seen at cryogenic temperatures, by decoupling substrate effects.

Contribution

The paper introduces a new device design that isolates graphene from substrate interactions, allowing room-temperature observation of quantum phenomena like the Kohn-anomaly.

Findings

Room-temperature gate-dependent Raman effects observed in graphene.

Decoupling substrate effects enables quantum phenomena detection at ambient conditions.

Device shows no background optical peaks or photodoping effects.

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 (hBN) substrate and gated with an ultra-thin gold (Au) 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 the observation of quantum phenomena at room temperature.