171 research outputs found
Superconducting fluctuations in organic molecular metals enhanced by Mott criticality
Unconventional superconductivity typically occurs in materials in which a
small change of a parameter such as bandwidth or doping leads to
antiferromagnetic or Mott insulating phases. As such competing phases are
approached, the properties of the superconductor often become increasingly
exotic. For example, in organic superconductors and underdoped
high- cuprate superconductors a fluctuating superconducting state
persists to temperatures significantly above . By studying alloys
of quasi-two-dimensional organic molecular metals in the
-(BEDT-TTF)X family, we reveal how the Nernst effect, a sensitive
probe of superconducting phase fluctuations, evolves in the regime of extreme
Mott criticality. We find strong evidence that, as the phase diagram is
traversed through superconductivity towards the Mott state, the temperature
scale for superconducting fluctuations increases dramatically, eventually
approaching the temperature at which quasiparticles become identifiable at all.Comment: 19 pages, 4 figures, 1 tabl
Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors
The phase diagram of the layered organic superconductor
-(ET)Cu[N(CN)]Cl has been accurately measured from a
combination of H NMR and AC susceptibility techniques under helium gas
pressure. The domains of stability of antiferromagnetic and superconducting
long-range orders in the pressure {\it vs} temperature plane have been
determined. Both phases overlap through a first-order boundary that separates
two regions of inhomogeneous phase coexistence. The boundary curve is found to
merge with another first order line related to the metal-insulator transition
in the paramagnetic region. This transition is found to evolve into a crossover
regime above a critical point at higher temperature. The whole phase diagram
features a point-like region where metallic, insulating, antiferromagnetic and
non s-wave superconducting phases all meet.Comment: 4 pages, 6 figures, Revte
Evaluation and design of multispecies cropping systems with perennials: are current methods applicable?
The existing methods are applicable to multispecies cropping systems with perennials. However, the particular features of these cropping systems highlight the drawbacks of each of them. Therefore, combining these approaches, where and when it is possible, should be preferred. Whatever the method, evaluation of the new systems requires new indicators development, to account for the multiple productions with very different timescales and serving varying objectives. Development of simple and effective sets of indicators adapted to these systems is a powerful tool to boost the design realm, for practitioners and researchers alike
Aperiodic quantum oscillations of particle-hole asymmetric Dirac cones
We report experimental measurements and theoretical analysis of Shubnikov-de
Haas (SdH) oscillations in a Dirac cone system: the a-(BEDT-TTF)2I3 organic
metal under hydrostatic pressure. The measured SdH oscillations reveal
anomalies at high magnetic fields B where the 1/B oscillations periodicity is
lost above 7 T. We interpret these unusual results within a theoretical model
that takes into account intrinsic distortions of the a-(BEDT-TTF)2I3 Dirac
cones such as a parabolic particle-hole asymmetric correction. Others possible
causes, such as a cone tilting or a Zeeman effect, are carefully ruled out. The
observations are consistent among a-(BEDT-TTF)2I3 samples with different Fermi
levels
Evaluation and design of multispecies cropping systems with perennials: are current methods applicable?
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The shock Hugoniot of hydroxy-terminated polybutadiene
The response of polymers to shock loading is becoming of increasing importance, both as binder systems in plastic-bonded explosives (PBXs) and as structural materials in their own right. In this paper, we report on the shock Hugoniot of hydroxy-terminated polybutadiene (HTPB), which is commonly used as a binder system in PBXs, but whose shock response has yet to be presented in the open literature. Results indicate that the shock velocity --- particle velocity relationship is linear, similar to some but not all polymer-based materials
A set of moment tensor potentials for zirconium with increasing complexity
Machine learning force fields (MLFFs) are an increasingly popular choice for
atomistic simulations due to their high fidelity and improvable nature. Here,
we propose a hybrid small-cell approach that combines attributes of both
offline and active learning to systematically expand a quantum mechanical (QM)
database while constructing MLFFs with increasing model complexity. Our MLFFs
employ the moment tensor potential formalism. During this process, we
quantitatively assessed structural properties, elastic properties, dimer
potential energies, melting temperatures, phase stability, point defect
formation energies, point defect migration energies, free surface energies, and
generalized stacking fault (GSF) energies of Zr as predicted by our MLFFs.
Unsurprisingly, model complexity has a positive correlation with prediction
accuracy. We also find that the MLFFs wee able to predict the properties of
out-of-sample configurations without directly including these specific
configurations in the training dataset. Additionally, we generated 100 MLFFs of
high complexity (1513 parameters each) that reached different local optima
during training. Their predictions cluster around the benchmark DFT values, but
subtle physical features such as the location of local minima on the GSFE
surface are washed out by statistical noise
Fruit-trees in agroforestry systems - review and prospects for the temperate and Mediterranean zones. Abstract number 33
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Haut parleur tout aimant guidé sur joint ferrofluide : caractérisation dynamique du guidage
Une étude expérimentale sur le comportement visqueux de ferrofluides, au sein d'une goutte insérée entre deux plans parallèles, en condition de cisaillement oscillatoire et sous champ magnétique homogène et stationnaire, permet d'alimenter un modèle pour les pertes d'un haut-parleur tout aimant guidé sur joint ferrofluide. Ces joints sont localisés dans les zones de fort gradient de champs magnétique. Le modèle de perte, fonction du volume, de la viscosité et de la saturation magnétique du ferrofluide, est alors validé par confrontation avec une expérience
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