472 research outputs found
Resistive switching induced by electronic avalanche breakdown in GaTaSeTe narrow gap Mott Insulators
Mott transitions induced by strong electric fields are receiving a growing
interest. Recent theoretical proposals have focused on the Zener dielectric
breakdown in Mott insulators, however experimental studies are still too scarce
to conclude about the mechanism. Here we report a study of the dielectric
breakdown in the narrow gap Mott insulators GaTaSeTe. We find
that the I-V characteristics and the magnitude of the threshold electric field
(E) do not correspond to a Zener breakdown, but rather to an avalanche
breakdown. E increases as a power law of the Mott Hubbard gap (E),
in surprising agreement with the universal law E E
reported for avalanche breakdown in semiconductors. However, the delay time for
the avalanche that we observe in Mott insulators is over three orders of
magnitude longer than in conventional semiconductors. Our results suggest that
the electric field induces local insulator-to-metal Mott transitions that
create conductive domains which grow to form filamentary paths across the
sample
First-Order Insulator-to-Metal Mott Transition in the Paramagnetic 3D System GaTa4Se8
The nature of the Mott transition in the absence of any symmetry braking
remains a matter of debate. We study the correlation-driven insulator-to-metal
transition in the prototypical 3D Mott system GaTa4Se8, as a function of
temperature and applied pressure. We report novel experiments on single
crystals, which demonstrate that the transition is of first order and follows
from the coexistence of two states, one insulating and one metallic, that we
toggle with a small bias current. We provide support for our findings by
contrasting the experimental data with calculations that combine local density
approximation with dynamical mean-field theory, which are in very good
agreement.Comment: 5 pages and 4 figures. Supplemental material: 2 pages, 2 figure
Dietary lipid level affects growth performance and nutrient utilisation of Senegalese sole (Solea senegalensis) juveniles
Over the last few years, several aspects of Senegalese sole (Solea senegalensis) culture have been developed and optimised but the dietary lipid level for optimal growth has never been determined. Hence, five isonitrogenous diets (56 % dietary protein) with increasing dietary lipid levels (4, 8, 12, 16 and 20 % DM) were fed to satiation to triplicate groups of twenty fish (mean initial weight 10 g). Fifteen tanks were randomly assigned one of the five diets. Feed was distributed using automatic feeders, and fish were fed over a 16-week period. At the end of the experiment the fish fed on diets containing the two lowest dietary lipid levels (4 and 8 %) showed a 3-fold body-weight increase with a significantly higher daily growth index than fish fed higher lipid levels (1-2 v. 0-8). Moreover, these fish displayed a significantly lower dry feed intake (12g/kg per d) and feed conversion ratio (1-0) compared with fish fed higher lipids levels (16-19 g/kg per d; feed conversion ratio 2-0). Low dietary lipid levels (< 12 %) significantly improved nutrient retention and gain and hence growth, without major effects on whole-body composition. Despite the slight alteration in n-3 PUFA muscle content in the fish fed low-fat-diets, this fish fed low dietary lipid still remains a rich n-3 PUFA product and generally maintained its nutritional value. These results evidenced a low lipid tolerance of Senegalese sole juveniles and suggest a maximal dietary inclusion level of 8 % lipids for both optimal growth and nutrient utilisation without compromising flesh quality.IDEIA; European fund FEDERinfo:eu-repo/semantics/publishedVersio
Universal electric-field-driven resistive transition in narrow-gap Mott insulators
One of today's most exciting research frontier and challenge in condensed
matter physics is known as Mottronics, whose goal is to incorporate strong
correlation effects into the realm of electronics. In fact, taming the Mott
insulator-to-metal transition (IMT), which is driven by strong electronic
correlation effects, holds the promise of a commutation speed set by a quantum
transition, and with negligible power dissipation. In this context, one
possible route to control the Mott transition is to electrostatically dope the
systems using strong dielectrics, in FET-like devices. Another possibility is
through resistive switching, that is, to induce the insulator-to-metal
transition by strong electric pulsing. This action brings the correlated system
far from equilibrium, rendering the exact treatment of the problem a difficult
challenge. Here, we show that existing theoretical predictions of the
off-equilibrium manybody problem err by orders of magnitudes, when compared to
experiments that we performed on three prototypical narrow gap Mott systems
V2-xCrxO3, NiS2-xSex and GaTa4Se8, and which also demonstrate a striking
universality of this Mott resistive transition (MRT). We then introduce and
numerically study a model based on key theoretically known physical features of
the Mott phenomenon in the Hubbard model. We find that our model predictions
are in very good agreement with the observed universal MRT and with a
non-trivial timedelay electric pulsing experiment, which we also report. Our
study demonstrates that the MRT can be associated to a dynamically directed
avalanche
Magnetoelastic polarons in the hole-doped quasi-one dimensional model system Y2-xCaxBaNiO5
October 4th, 2004Charge transport in the hole-doped quasi-1D model system YCaBaNiO (x 0.15) is investigated in the 50-300 K temperature range. The resistivity temperature dependence is characterized by a constant activation energy 1830 K at room temperature while decreases upon cooling. We suggest that measures the binding energy of the doped holes which form magneto-acoustic polarons when polarizing the neighboring Ni spins. A semi-classical model is proposed which allows to relate the electrical measurements and the bulk magnetic susceptibility. This model gives a picture of the spin-charge-lattice relation in this inhomogeneously doped quasi-1D system and explains its unusual one-particle charge excitation spectrum close to the Fermi level
Magnetoelastic polarons in the hole-doped quasi-one dimensional model system Y2-xCaxBaNiO5
Charge transport in the hole-doped quasi-1D model system
YCaBaNiO (x 0.15) is investigated in the 50-300 K
temperature range. The resistivity temperature dependence is characterized by a
constant activation energy 1830 K at room temperature while
decreases upon cooling. We suggest that measures the binding
energy of the doped holes which form magneto-acoustic polarons when polarizing
the neighboring Ni spins. A semi-classical model is proposed which allows to
relate the electrical measurements and the bulk magnetic susceptibility. This
model gives a picture of the spin-charge-lattice relation in this
inhomogeneously doped quasi-1D system and explains its unusual one-particle
charge excitation spectrum close to the Fermi level.Comment: October 4th, 200
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