Carbon-nanotube-based terahertz-to-optics rectenna (CANTOR-FP7-PEOPLE-IRSES-612285)

The main goal of the project is to combine the efforts of scientific teams from Britain, Israel and Belarus in developing a theoretical basis for the use of carbon nanotube antennas for rectification and detection of electromagnetic radiation in terahertz and optical ranges. To reach the main project goal, we will combine the efforts of the international consortium on the following objectives: - to extend the Landauer-Büttiker theory of electron transport to the case of photon-dressed electrons; - to analyze theoretically the rectenna performance with photon-dressed electrons as working substance; - to estimate thermodynamically the ultimate rectenna efficiency stipulated by the entropy transfer in photo-assisted tunneling. The Project Consortium joins representatives of different scientific communities under the common roof of interdisciplinary research in theoretical modeling of nanorectenna which contributes to the problem of the solar energy conversion to electricity. The combined effort of teams with the different background and experience provides the complementarity/synergy between the partners stimulating the generation of new knowledge directly related to quantum optics of carbon nanostructures and aimed towards the progress in sunlight conversion into electric power. The main scientific results obtained within the second two-year period of the project in accordance with the project tasks and deliverables are as follows: We analysed numerically and analytically the observable dc currents in a nanojunction within the density operator formalism. The dc conductivity was analyzed for different states of dressing light (photon vacuum, single-photon state, coherent state) and compared with the Landauer conductivity for free electrons. A proper description of the dressed electron transport through a nanogap contact has been elaborated and dessiminated among the researchers from different fields, such as physics and technology of semiconductor and carbon nanostructures, electromagnetics and optics, etc. The essential contribution of the low dimensionality into the conductivity of nanojunctions has been found to be benefecial for the optical rectification and of terahertz-to-optical radiation. We considered the effect of rectification related to the asymmetry inherent to the system. Application of a magnetostatic field is one of the possible mechanisms of the asymmetry. Contrary to the standard Landauer-Buttiker theory, where the magnetostatic field impact has been studied as a factor producing the spin effect influence on the quantum transport through a nanogap and the magnetic field is normal to nanojunction axis, we considered a homogeneous magnetic field directed axially with carbon nanotube. Applying electrical potential to be rectified to the contact points of the leads, we evaluated the dc current dependence on the magnetic flux through the carbon nanotube cross-section. This allowed us to analyze the possibility of rectification efficiency enhancement by varying the magnetic flux. This analysis show promissing results for carbon nanotubes applications in Vivaldy antennas when contact region exposed to a magnetic field of an arbitrary orientation. One of the main project achievements was developing of the model of electron transport through the nano-rectenna. The model is based on the quantum theory of open systems. We demonstrated theoretically and experimentally that such systems can perform optical equalization to smooth multimode light or act as a distributor, guiding it into selected channels. Quantum thermodynamically, these systems can act as catalytic coherent reservoirs. This opens the way of the entropy transfer and high-efficient generation of the heat flux. We also analyzed dynamics of coupled quantum systems. It has been found, noisy coupling between individual quantum systems leads to diffusive lossless energy transfer and retain quantum character of stationary states. Diffusive dynamics persists even in the case where additional noise suppresses all unitary excitation exchange: arbitrarily strong local dephasing, while destroying quantum correlations, does not affect energy transfer. The noisy coupling opens a new way of the high-efficient type of energy transfer, which makes it promising for applications in solar energetic. We showed that the observable values of the electromagnetic field in the far- and near-field zones emitted and absorbed by the quantum nanoantenna are coupled via uncertainty relations of the Heisenberg type. The similar uncertainty inequalities have been obtained for the electric currents in the different branches of the quantum networks. On this basis we determined the fundamental physical limitations of quantum antennas efficiency. We also carried out a physical analysis of the rectification mechanism and its relation to the process of generation of terahertz radiation by Rabi-Bloch oscillations in the chains of two-level real or artificial atoms coupled via inter-atomic tunneling. A a crucial step towards a mesoscopic nanorectenna theory was investigation of the problem of electromagnetic scattering by a finite-length nanowire with a number of embedded mesoscopic objects. The developed theory is based on combining the integral equations of the classical antenna theory (Hallén-type equations) with the quantum transport formalism equations comprise the integral operators of wire antennas and algebraic terms responsible for the mesoscopic systems. By means of this theory, it has been shown that stand-alone finite-length carbon tube with a short low-conductive section is promising for the realization of nanoantennas in the terahertz frequency range. Productive collaboration between the scientific teams has allowed to carry out preliminary experimental verification of a number of theoretical results. In particular, theoretical and experimental investigations of the electromagnetic parameters of single-walled carbon nanotube (SWCNT) from 30 GHz to 2 THz has been carried out. These investigations showed that screening effect in finite-length carbon nanotubes hinders significantly the electromagnetic response of canbon nanotube antenna and there is a strong frequency dependence of the electromagnetic response of CNT. We have also shown in experiment, that the CNT electron scattering rate in the terahertz range is directly proportional to the temperature for 300–500 K, revealing electron-acoustic phonon scattering as the main scattering mechanism in the individual CNTs. This mechanism should be taken into account as the main mechanism of energy dissipation in the CNT antenna. During the second two-year period of the project the Consortium organized a set of knowledge transfer events in accordance with project milestones. These events included four special sessions at major international conferences and a focused advance research workshop. Over the reported period CANTOR consortium members published three book chapters and over 25 papers in peer-reviewed journals and conference proceedings, delivered 38 oral presentations at international conferences and workshops. More than a half of all the talks [63% or 24 presentation] at the international conferences were invited ones. This is a clear evidence that consortium has managed to generate by its results a mass interest among the vast diversity of scientific communities. In summary, the project has made a significant contribution towards the fast developing area of science and engineering of new artificial materials for solar energy conversion. It has outlined new directions for technological development.