1,608 research outputs found
Anomalies in Universal Intensity Scaling in Ultrarelativistic Laser-Plasma Interactions
Laser light incident on targets at intensities such that the electron
dynamics is ultrarelativistic gives rise to a harmonic power spectrum extending
to high orders and characterized by a relatively slow decay with the harmonic
number m that follows a power law dependence, m^{-p}. Relativistic similarity
theory predicts a universal value for p = 8/3 up to some cut-off m = m*. The
results presented in this work suggest that under conditions in which plasma
effects contribute to the emission spectrum, the extent of this contribution
may invalidate the concept of universal decay. We report a decay with harmonic
number in the ultrarelativistic range characterised by an index 5/3 < p < 7/3,
significantly weaker than that predicted by the similarity model.Comment: 5 pages, 4 figure
Solvable Leibniz algebras with triangular nilradical
A classification exists for Lie algebras whose nilradical is the triangular
Lie algebra . We extend this result to a classification of all solvable
Leibniz algebras with nilradical . As an example we show the complete
classification of all Leibniz algebras whose nilradical is .Comment: arXiv admin note: text overlap with arXiv:1307.844
Tuning crystal ordering, electronic structure, and morphology in organic semiconductors: Tetrathiafulvalenes as a model case
Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF-derivatives are ideal candidates to perform molecule-property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state-of-the-art of the field-effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure-performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p-channel, n-channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source-drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications. Tetrathiafulvalenes are promising active materials in organic field-effect transistors (OFETs), in which they exhibit high performances. An overview is provided of the use of this family of materials as a model building block for OFETs to highlight general concepts of organic semiconductors and their use in devices.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with projects BE-WELL CTQ2013-40480-R and MAT2012-30924, and the Generalitat de Catalunya (2014-SGR-17, 2014SGR97 and XRQTC).Peer Reviewe
Exchange coupling inversion in a high-spin organic triradical molecule
The magnetic properties of a nanoscale system are inextricably linked to its
local environment. In ad-atoms on surfaces and inorganic layered structures the
exchange interactions result from the relative lattice positions, layer
thicknesses and other environmental parameters. Here, we report on a
sample-dependent sign inversion of the magnetic exchange coupling between the
three unpaired spins of an organic triradical molecule embedded in a
three-terminal device. This ferro-to-antiferromagnetic transition is due to
structural distortions and results in a high-to-low spin ground state change in
a molecule traditionally considered to be a robust high-spin quartet. Moreover,
the flexibility of the molecule yields an in-situ electric tunability of the
exchange coupling via the gate electrode. These findings open a route to the
controlled reversal of the magnetic states in organic molecule-based
nanodevices by mechanical means, electrical gating or chemical tailoring
Multi-Orbital Molecular Compound (TTM-TTP)I_3: Effective Model and Fragment Decomposition
The electronic structure of the molecular compound (TTM-TTP)I_3, which
exhibits a peculiar intra-molecular charge ordering, has been studied using
multi-configuration ab initio calculations. First we derive an effective
Hubbard-type model based on the molecular orbitals (MOs) of TTM-TTP; we set up
a two-orbital Hamiltonian for the two MOs near the Fermi energy and determine
its full parameters: the transfer integrals, the Coulomb and exchange
interactions. The tight-binding band structure obtained from these transfer
integrals is consistent with the result of the direct band calculation based on
density functional theory. Then, by decomposing the frontier MOs into two
parts, i.e., fragments, we find that the stacked TTM-TTP molecules can be
described by a two-leg ladder model, while the inter-fragment Coulomb energies
are scaled to the inverse of their distances. This result indicates that the
fragment picture that we proposed earlier [M.-L. Bonnet et al.: J. Chem. Phys.
132 (2010) 214705] successfully describes the low-energy properties of this
compound.Comment: 5 pages, 4 figures, published versio
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