Metallic carbon nanotube quantum dots with broken symmetries as a platform for tunable terahertz detection

Abstract

Generating and detecting radiation in the technologically relevant range of the so-called terahertz gap (0.1 − 10 THz) is challenging because of a lack of efficient sources and detectors. Quantum dots in carbon nanotubes have shown great potential to build sensitive terahertz detectors usually based on photon-assisted tunnelling. A recently reported mechanism combining resonant quantum dot transitions and tunnelling barriers asymmetries results in a narrow linewidth photocurrent response with a large signal-to-noise ratio under weak THz radiation. That device was sensitive to one frequency, corresponding to transitions between equidistant quantized states. In this work we show, using numerical together with scanning tunnelling spectroscopy studies of a defect-induced metallic zigzag single-walled carbon nanotube quantum dot that simultaneously breaking various symmetries in metallic nanotube quantum dots of arbitrary chirality strongly relaxes the selection rules in the electric dipole approximation, and removes energy degeneracies. This leads to a richer set of allowed optical transitions spanning frequencies from 1 THz to several tens of THz, for a ∼10 nm quantum dot. Based on these findings, we propose a terahertz detector device based on a metallic single-walled carbon nanotube quantum dot defined by artificial defects. Depending on its length and contacts transparency, the operating regimes range from a high-resolution gate-tunable terahertz sensor to a broadband terahertz detector. Our calculations indicate that the device is largely unaffected by temperatures up to 100 K, making carbon nanotube quantum dots with broken symmetries a promising platform to design tunable terahertz detectors that could operate at liquid nitrogen temperatures.

Optical modulation of hole doping via atomically thin fluorine-functionalized graphene endowed transparent and flexible UV-photodetector

“…In CQD cases, on the other hand, the effective suppression of hole mobility (23.7 cm 2 /Vs) is identi ed due to defect-induced coulomb scattering of transported holes con gured by abundant oxygencontaining groups and surface-bound defective states. 20 When incorporating CQDs with FF-Gra as heterostructures, we barely observe the signi cant modulation of dark-current characteristics where the involved I-T behaviors resemble to that of bare CQDs. In fact, the associated band diagram of incorporated CQD/FF-Gra essentially points out the charge transfer across the created heterojunction from the consequence of leveraging the difference of Fermi level (φ, φ of FF-Gra = 4.81 eV and φ of CQD = 5.67 eV) at both sides, as evidenced in Figure S6; yet the contradicted result in viewing the hole transport stands against such normal circumstances.…”

Modification of the optical properties of molecular chains upon coupling to adatoms

“…Coupling the adatom may result in symmetry breaking of the structure leading to a modification of its electronic properties and optical response [37]. Here, we aim to identify the parameters in the system that-if altered-influence these properties most sensitively.…”