THz and microwave properties of 3D-printed nanocarbon based multilayers

We propose a new type of light-weight conductive thin film material having good mechanical properties and electromagnetic shielding efficiency. For that 3D printing through layer-to-layer deposition of nanocarbon containing plastic layers and neat polymer layers was combined with hot pressing to obtain 10 μm thick films. We show that such composite has Re ε ≈ Im ε in very broad frequency range, 200GHz-0.6 THz

QED radiative correction to spin-density matrix elements in exclusive vector meson production

QED radiative effects are considered in the case of measurement of spin-density matrix elements of diffractive $\rho$-meson electroproduction. Large radiative correction for $r^5_{00}$ is found in the kinematics of collider experiments at HERA.Comment: 7 pages, 5 figure

Normal stress differences in non-Brownian fiber suspensions

International audienceIn this paper, we present an experimental study of the normal stress differences that arise in non-Brownian rigid fiber suspensions subject to a shear flow. While early measurements of the normal stress in fiber suspensions in Newtonian fluids measured only N 1 − N 2 , the recent work of Snook et al. J. Fluid Mech. 758 486 (2014) and the present paper provide the first measurements of N 1 and N 2 separately. Snook et al perform such measurements with a gap that is very wide compared with the fiber length, whereas the present paper explores the effects of confinement when the gap is 4-10 times the fiber length. The first and the second normal stress differences are measured using a single experiment which consists of determining the radial profile of the second normal stress, along the velocity gradient direction, Σ 22 , in a torsional flow between two parallel discs. Suspensions are made of monodisperse fibers immersed in a neutrally buoyant Newtonian fluid. Two fiber lengths and three aspect ratios a r = L/d, and a wide range of concentrations have been tested. N 1 is found to be positive while N 2 is negative and the magnitude of both normal stress differences increases when nL 2 d increases, n being the number fraction of fibers. The magnitude of N 2 is found to be much smaller than N 1 only for high aspect ratios and low fiber concentrations

Carbon nanotube array as a van der Waals two-dimensional hyperbolic material

We use an ab-initio approach to design and study a novel two-dimensional material - a planar array of carbon nanotubes separated by an optimal distance defined by the van der Waals interaction. We show that the energy spectrum for an array of quasi-metallic nanotubes is described by a strongly anisotropic hyperbolic dispersion and formulate a model low-energy Hamiltonian for its semi-analytical treatment. Periodic-potential-induced lifting of the valley degeneracy for an array of zigzag narrow-gap nanotubes leads to the band gap collapse. In contrast, the band gap is opened in an array of gapless armchair tubes. These unusual spectra, marked by pronounced van Hove singularities in the low-energy density of states, open the opportunity for interesting physical effects and prospective optoelectronic applications

Apparent yield stress in rigid fibre suspensions: the role of attractive colloidal interactions

International audienceThis work is focused on the modelling of the shear and normal stresses in fibre suspensions that are subjected to a simple shear flow in the presence of short-range lubrication forces, van der Waals and electrostatic forces, as well as solid friction forces between fibres. All these forces are weighed by the contact probability. The theory is developed for attractive fibres with van der Waals interaction dominating over electrostatic repulsion. The model predicts a simple Bingham law for both the shear stress and the first normal stress difference with the apparent shear and normal yield stresses proportional, respectively, to the second and the third power of particle volume fraction. The model is applied to the experimental data of Rakatekar et al. Adv. Mater 21, 874-878 (2009) and Natale et al. AIChE J. 60, 1476-1487 (2014) on the suspensions of carbon nanotubes dispersed in a Newtonian epoxy resin. It reproduces well the quadratic dependency of the apparent yield stress on particle volume fraction (σ Y ∝φ^2) for average particle aspect ratios of r=160 and 1200, while it underpredicts the power-law exponent for rD80 (always predictingφ^2 behaviour instead of φ^3.2

Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes

We measure the conductivity spectra of thin films comprising bundled single-walled carbon nanotubes (CNTs) of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed temperature-induced changes in the terahertz conductivity spectra are shown to depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which we obtain from Drude fits of the measured conductivity in the range 0.3-2 THz for 10 $\mu$m length CNTs. This increasing scattering rate with temperature results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS$_2$ nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8 figures. Supplementary material: 5 pages, 6 figure

Quantum entanglement in electric circuits: From anomalous crosstalk to electromagnetic compatibility in nano-electronics

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record..We show that the electromagnetic coupling at the nanoscale may be accompanied by another coupling mechanism, related to quantum entanglement. Consequently, a combined 'electromagnetic-quantum' coupling is created, which stipulates long-distance and long-living interactions in electric circuits. Manifestation of this effect in electromagnetic compatibility (EMC) is discussed. An efficient theoretical framework for EMC analysis in nanoelectronics is developed based on the generalized theory of electric circuits. It is shown that the action of quantum entanglement is equivalent to an addition of the supplementary elements in electric circuit with the effective admittances defined as general susceptibilities that can be calculated using the Kubo-technique.This work was supported in part by EU grants FP7-PEOPLE-2009-IRSES- 247007 CACOMEL and FP7-PEOPLE-2013-IRSES- 612285 CANTOR

Anomalous electromagnetic coupling via entanglement at the nanoscale

This is the final version of the article. Available from IoP Publishing via the DOI in this record.Understanding unwanted mutual interactions between devices at the nanoscale is crucial for the study of the electromagnetic compatibility in nanoelectronic and nanophotonic systems. Anomalous electromagnetic coupling (crosstalk) between nanodevices may arise from the combination of electromagnetic interaction and quantum entanglement. In this paper we study in detail the crosstalk between two identical nanodevices, each consisting of a quantum emitter (atom, quantum dot, etc), capacitively coupled to a pair of nanoelectrodes. Using the generalized susceptibility concept, the overall system is modeled as a two-port within the framework of the electrical circuit theory and it is characterized by the admittance matrix. We show that the entanglement changes dramatically the physical picture of the electromagnetic crosstalk. In particular, the excitation produced in one of the ports may be redistributed in equal parts between both the ports, in spite of the rather small electromagnetic interactions. Such an anomalous crosstalk is expected to appear at optical frequencies in lateral GaAs double quantum dots. A possible experimental set up is also discussed. The classical concepts of interference in the operation of electronic devices, which have been known since the early days of radio-communications and are associated with electromagnetic compatibility, should then be reconsidered at the nanoscale.This research was supported in part by the EU Horizon 2020 project H2020-MSCA-RISE-2014-644076 CoExAN and EU FP7 projects, FP7-PEOPLE-2012-IRSES-316432 QOCaN and FP7-PEOPLE-2013-IRSES-612285 CANTOR. Discussions of the basic ideas underlying this work with Dr S Starobinets and Dr D Mogilevtsev are acknowledged