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 Pulse Induced Resistive Switching, Electronic Phase Separation, and Possible Superconductivity in a Mott insulator

Metal-insulator transitions (MIT) belong to a class of fascinating physical phenomena, which includes superconductivity, and colossal magnetoresistance (CMR), that are associated with drastic modifications of electrical resistance. In transition metal compounds, MIT are often related to the presence of strong electronic correlations that drive the system into a Mott insulator state. In these systems the MIT is usually tuned by electron doping or by applying an external pressure. However, it was noted recently that a Mott insulator should also be sensitive to other external perturbations such as an electric field. We report here the first experimental evidence of a non-volatile electric-pulse-induced insulator-to-metal transition and possible superconductivity in the Mott insulator GaTa4Se8. Our Scanning Tunneling Microscopy experiments show that this unconventional response of the system to short electric pulses arises from a nanometer scale Electronic Phase Separation (EPS) generated in the bulk material.Comment: Highlight in Advanced Functional Materials 18, 1-4 (2008) doi : 10.1002/adfm.20080055

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

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

Defects and localization in chemically-derived graphene

We have performed electron spin resonance (ESR) measurements on a large assembly of graphene oxide (GO) and reduced graphene oxide (RGO) flakes. In GO samples the Curie tail is coming from 1.4 x 10(18) cm(-3) of localized spins. Although reduction of GO was expected to reestablish the pristine properties of graphene, no Pauli-like contribution was detected and only a low concentration of 1.2 x 10(16) cm(-3) spin carrying defects were measured. Our study, completed by resistivity measurements, shows that the carrier transport in RGO samples is dominated by hopping. The incomplete reduction of GO leaves behind a large number of defects, presumably the majority of which are ESR silent, causing the Anderson localization of the electronic states. Slight doping with potassium indicates the appearance of a Pauli contribution in the spin susceptibility

Synthesis, electrical resistivity, thermo-electric power and magnetization of cubic ZnMnO3

Cubic ZnMnO3 powder in the form of well-crystalline nanoflakes have been synthesized at low temperatures from a nitrate precursor. The electrical properties of cubic ZuMnO(3) samples have been established by DC resistivity (rho) and thermo-electric power (Seebeck coefficient) measurements on a pressed pellet. The material exhibits insulator behavior with 0.7 eV acceptor ionization energy in the measured temperature range of 170-300 K. The thermo-electric power indicates a positive sign of the charge carriers. The obtained material exhibits a superparamagnetic signature with a blocking temperature of 9 K and the ZFC-FC splitting temperature of 15 K. (C) 2010 Elsevier Ltd. All rights reserved

Structural and magnetic behaviour of SmCo4/alpha-Fe nanocomposites obtained by mechanical milling and subsequent annealing

International audienceSmCo5+20%Fe magnetic nanocomposites have been obtained by mechanical milling in a planetary mill and subsequent annealing. The influence of the milling and annealing conditions on the magnetic and structural behaviour of SmCo5/alpha-Fe has been studied by X-ray diffraction, electron microscopy, magnetic measurements and Mossbauer spectrometry

Evidence from thermodynamic measurements for a singlet crystal-field ground state in pyrochlore Tb2Sn2O7 and Tb2Ti2O7

The magnetic entropy variation for the ordered spin-ice Tb2Sn2O7 and the spin-liquid Tb2Ti2O7 measured up to similar to 20 K shows that the crystal-field ground state for both systems is a singlet split from the first excited level by a thermal energy of similar to 2 K. It is the superexchange interactions between the Tb3+ spins which induce the terbium magnetic moments. Our results are analyzed in terms of a tetragonal perturbation for Tb2Ti2O7 and this perturbation plus a molecular field for Tb2Sn2O7

Half-Metallic Ferromagnetism and Large Negative Magnetoresistance in the New Lacunar Spinel GaTi3VS8

International audienceThe lacunar spinel compounds GaTi4-xNxS8 (0 < x < 4), consisting of Ti4-xVx tetrahedral clusters, were prepared and their structures were determined by powder X-ray diffraction. The electronic structures of GaTi4-xVxS8 (x = 0, 1, 2, 3) were examined by density functional calculations, and the electrical resistivity and magnetic susceptibility of these compounds were measured. Our calculations predict that GaTi3VS8 is a ferromagnetic half-metal, and this prediction was confirmed by magnetotransport experiments performed on polycrystalline samples of GaTi3VS8. The latter reveal a large negative magnetoresistance (up to 22% at 2 K), which is consistent with the intergrain tunnelling magnetoresistance expected for powder samples of a ferromagnetic half-metal and indicates the presence of high spin polarization greater than 53% in GaTi3VS8