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 Y$_{2-x}$Ca$_x$BaNiO$_5$ (x $\\leq$ 0.15) is investigated in the 50-300 K temperature range. The resistivity temperature dependence is characterized by a constant activation energy $E_{a}/k_{B}\\sim$ 1830 K at room temperature while $E_{a}$ decreases upon cooling. We suggest that $E_{a}$ 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

Electric pulse induced electronic patchwork in the Mott insulator GaTa4Se8

Following a recent discovery of the Insulator-to-Metal Transition induced by electric field in GaTa4Se8, we performed a detailed Scanning Tunneling Microscopy/Spectroscopy study of both pristine (insulating) and transited (conducting) crystals of this narrow gap Mott insulator. The spectroscopic maps show that pristine samples are spatially homogeneous insulators while the transited samples reveal at nanometer scale a complex electronic pattern that consists of metallic and superinsulating patches immersed in the pristine insulating matrix. Surprisingly, both kinds of patches are accompanied by a strong local topographic inflation, thus evidencing for a strong electron-lattice coupling involved in this metal-insulator transition. Finally, using a strong electric field generated across the STM tunneling junction, we demonstrate the possibility to trig the metal-insulator transition locally even at room temperature

Electric field Assisted Nanostucturing of a Mott Insulator

Accepted for Advanced Functional Materials Published as : Adv Funct Mat Vol 19 p 2800 (2009)International audienceWe report the first experimental evidence for a strong electromechanical coupling in the Mott insulator GaTa4Se8 allowing a highly reproducible nano-writing with a Scanning Tunneling Microscope (STM). The local electric field across the STM junction is observed to have a threshold value above which the clean (100) surface of GaTa4Se8 becomes mechanically instable: At voltage biases V > 1.1V the surface suddenly inflates and comes in contact with the STM tip, resulting in nanometer size craters. The formed pattern can be indestructibly “read” by STM at lower voltage bias, thus allowing a 5 Tdots/inch2 dense writing/reading at room temperature. The discovery of the electromechanical coupling in GaTa4Se8 might give new clues in the understanding of the Electric Pulse Induced Resistive Switching recently observed in this stoechiometric Mott insulator

Ultrafast filling of an electronic pseudogap in photoexcited (LaS) 1.196 VS 2

We investigate by angle and time resolved photoemission spectroscopy the unusual insulating state of strongly distorted triangular V slabs in (LaS)1.196VS2. We show that the electronic structure is dominated by the lowest band of the V t2g manifold, which disperses over 0.7 eV and is nearly filled. Hence, (LaS)1.196VS2 is not a Mott insulator. The spectra are strongly temperature dependent, shifting by 100 meV upon cooling to 50 K. The sudden photoexcitation at 50K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable timescale. We conclude that a very strong electron-phonon coupling makes this state extremely sensitive to small perturbations of the V clusters distortions

New Trends in Beverage Packaging Systems: A Review

New trends in beverage packaging are focusing on the structure modification of packaging materials and the development of new active and/or intelligent systems, which can interact with the product or its environment, improving the conservation of beverages, such as wine, juice or beer, customer acceptability, and food security. In this paper, the main nutritional and organoleptic degradation processes of beverages, such as oxidative degradation or changes in the aromatic profiles, which influence their color and volatile composition are summarized. Finally, the description of the current situation of beverage packaging materials and new possible, emerging strategies to overcome some of the pending issues are discussed

Dielectric breakdown and current switching effect in the incommensurate layered compound (LaS)(1.196)VS2

International audienceA current switching effect of several orders of magnitude was observed in the incommensurate misfit layered compound (LaS)(1.196)VS2. This effect involves correlated vanadium t(2g) states in a hexagonal [VS2] layer. Application of moderate electric fields (similar to 50 V/cm) induces a dielectric breakdown and restores a metallic state. The large pretransitional nonlinearities are consistent with a Poole-Frenkel mechanism which highlights the role of Coulomb interactions. This behavior and the strong modulation of the vanadium atom positions, revealed by single crystal x-ray structure determination, are in favor of a heterogeneous charge distribution. With respect to recent theoretical works, we suggest that the current switching effect observed in (LaS)(1.196)VS2 is related to the breakdown of a remaining Mott insulator state

Control of the Electronic Properties and Resistive Switching in the New Series of Mott Insulators GaTa(4)Se(8-y)Te(y) (0 <= y <= 6.5)

International audienceWe report here the substitution of Se by Te in the Mott insulator GaTa4Se8-yTey, a lacunar spinel compound containing Ta4 tetrahedral clusters. Our synthetic and crystallographic works show that Te atoms occupy successively two different crystallographic sites and that the substitution reaches a limit for GaTa4Se1.5Te6.5. Band structure calculations and transport measurements demonstrate that this substitution induces for low Te doping (0 ≤ y ≤ 4) an increase of the band gap related to a narrowing of the d bands (i.e., a negative chemical pressure effect). Conversely, for higher Te doping (y ≥ 4), a decrease of the band gap is observed, while the bandwidth of the d bands stays almost constant. This result suggests that the partial declusterization of Ta4 tetrahedra observed at high Te doping (y ≥ 4) leads to a very unusual reduction of the electronic repulsion energy (U) that opens the gap between the lower and upper Hubbard bands. The GaTa4Se8-yTey compounds therefore provide, to our knowledge, the first example of a U-controlled tuning of electronic properties in a Mott insulator. Moreover, we show that the substitution of Se by Te in GaTa4Se8-yTey does not affect drastically the reversible and nonvolatile electric pulse-induced resistive switching phenomena discovered recently in the nonsubstituted compound GaTa4Se8

Ba 2 F 2 Fe 1.5 Se 3 : An Intergrowth Compound Containing Iron Selenide Layers

International audienc

Élaboration de couches minces de GaV4S8 par pulvérisation magnétron (du matériau au premier dispositif pour mémoire à transition résistive (RRAM))

Les composés de la famille des spinelles lacunaires AM4X8 (A = Ga, Ge ; M = V, Ta, Nb ; X = S, Se) sont des isolants de Mott à faible gap dans lesquels l'application de pulses électriques induit une chute de résistance électrique. Cette "transition résistive" non-volatile et réversible, observée sur mono-cristaux, est potentiellement intéressante dans des applications de type mémoire RRAM. Pour cela, un des principaux challenges consiste à obtenir ces matériaux chalcogénures sous forme de couches minces. Dans ce travail, nous avons synthétisé, par pulvérisation RF magnétron et pour la première fois, des couches minces du composé GaV4S8. Cette technique, compatible avec les étapes technologiques de la microélectronique, a nécessité la réalisation de cibles de pulvérisation de compacité supérieure à 90%. L'étude paramétrique des conditions de dépôt et de recuit a permis d'obtenir des couches minces cristallines et stoechiométriques ayant des propriétés électroniques identiques à celles du matériau massif. À température ambiante, les couches minces présentent les propriétés de transition résistive et de cyclage induits par pulses électriques. L'étude de la transition résistive révèle l'existence d'un champ électrique seuil, ce qui suggère que celle-ci est liée à un effet de champ électrique. L'ensemble des études réalisées indique d'une part que le mécanisme de la transition résistive diffère de ceux répertoriés jusqu'ici dans la littérature et d'autre part que les principales caractéristiques du cyclage (amplitude, temps, tension de commutation) se comparent très favorablement à celles des autres types de mémoires non-volatiles émergentesThe compounds of the lacunar spinel family AM4X8 (A = Ga, Ge ; M = V, Ta, Nb ; X = S, Se) are small gap Mott insulators which undergo a resistive switching under electric pulses. This non-volatile and reversible switching, discovered on single crystals, has potential applications in the field of RRAM non-volatile memories. To unlock this potential, a major challenge, the deposition of these chalcogenide materials in thin layers, remains. In this work, GaV4S8 thin layers were synthesized for the first time, using RF magnetron sputtering. This technique is compatible with the current technological fabrication steps used in microelectronics. We first prepared sputtering targets with a compacity higher than 90%. Through a thorough parametric study of the deposition and annealing conditions, crystallized and stoichiometric thin layers have been obtained with electronic properties identical to the bulk material. At room temperature, the thin layers exhibit both the resistive switching and cycling property induced by electric pulses. The study on the resistive switching reveals the existence of a threshold electric field, which suggests that it is related to an electric field effect. Our entire study demonstrates, on the one hand, that the mechanism behind the resistive switching differs from those identified in other systems reported so far and, on the other hand, that the cycling characteristics (amplitude, switching time and voltage) of GaV4S8 are competitive with respect to those encountered in other kind of emerging non-volatile memoriesNANTES-BU Sciences (441092104) / SudocSudocFranceF

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 Y$_{2-x}$Ca$_x$BaNiO$_5$ (x $\\leq$ 0.15) is investigated in the 50-300 K temperature range. The resistivity temperature dependence is characterized by a constant activation energy $E_{a}/k_{B}\\sim$ 1830 K at room temperature while $E_{a}$ decreases upon cooling. We suggest that $E_{a}$ 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