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

arXiv:2006.10837v2
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 tunneling. A recently reported mechanism combining resonant quantum dot transitions and tunneling barrier 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 simulations together with scanning tunneling spectroscopy studies of a defect-induced metallic zigzag single-walled carbon nanotube quantum dot, that breaking simultaneously 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.
This work has been partially supported by the Spanish Ministry of Science and Innovation with PID2019-105488GB-I00 and PCI2019-103657 (A.A.) and FIS2017-82804-P (D.B.). The work of D.B. is partially supported by by the Transnational Common Laboratory QuantumChemPhys. The Basque Government supported this work through Project No. IT-1246-19 (A.A.). J.W.G. acknowledges financial support from FONDECYT: Iniciación en Investigación 2019 Grant N. 11190934 (Chile). A.A. acknowledge financial support by the European Commission from the NRG-STORAGE project (GA 870114). K.E., C.P. and D.P. acknowledge the Swiss National Science Foundation under Grant No. 200020_182015 and No. 200021_172527, and the NCCR MARVEL funded by the Swiss National Science Foundation (51NF40-182892). The Swiss National Supercomputing Centre (CSCS) under project ID s746 and s904 is acknowledged for computational resources.