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

Les conducteurs ioniques LiMCl4 (M = Fe, Al) et Li1+xFeCl4 : etudes physicochimiques par spectroscopie Mossbauer et resonance magnetique nucleaire

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Quantitative Raman calibration of sulfate-bearing polymineralic mixtures: a S quantification in sedimentary rocks on Mars

International audienc

Bis(1-ethyl-3-methylimidazolium) 3,6-diselanylidene-1,2,4,5-tetraselena-3,6-diphosphacyclohexane-3,6-diselenolate

In the title compound, 2C6H11N2+·P2Se82− or [EMIM]2P2Se8 (EMIM = 1-ethyl-3-methylimidazolium), the anions, located about inversion centers between EMIM cations, exhibit a cyclohexane-like chair conformation. The cations are found in columns along the a axis, with centroid–centroid distances of 3.8399 (3) and 4.7530 (2) Å. The observed P—Se distances and Se—P—Se angles agree with other salts of this anion

Lead-antimony sulfosalts from Tuscany (Italy). XI. The new mineral species parasterryite, Ag4Pb20(Sb14.5As 9.5)Σ24 S58, and associated sterryite, Cu(Ag,Cu)3Pb19(Sb,As)22(As-As)S56, from the Pollone mine, Tuscany, Italy

The new mineral species parasterryite has been discovered in the Pollone barite - pyrite - (Pb-Zn-Ag) deposit at Valdicastello Carducci, near Pietrasanta, in the Apuan Alps, Tuscany, Italy. It forms acicular crystals up to 4 × 0.3 mm in vugs in quartz-barite veins. Sterryite (second world occurrence) also is present. The associated sulfides and sulfosalts are pyrite, sphalerite and various Sb-As sulfosalts. Parasterryite is black and metallic. Under the microscope, it is white with weak pleochroism; anisotropism is distinct with greenish and brownish tints. Data on maximum and minimum reflectances for the COM wavelengths are [λ (nm), Rair, R oil(%)]470: 35.1,40.8 and 19.4, 22.2,546: 33.5, 39.3 and 19.3, 21.7, 589: 32.7, 38.2 and 18.7, 21.1, 650: 31.4, 36.5 and 17.3, 19.5. Hardness VHN10 = 238 kg/mm2. An electron-microprobe analysis gave (in wt.%, mean result of 32 spot analyses): Cu 0.09(2), Ag 4.36(6), Hg 0.15(2), Pb 47.00( 18), Sb 19.57(30), As 7.73(21 ), S 20.56(7), total 99.46(23). A single-crystal X-ray study of parasterryite indicates monoclinic symmetry, space group P21/c, with a 8.3965(5), b 27.9540(4), c 43.8840(13) Å, β 90.061(12)°, V= 10300(3) Å3. The main powder-diffraction lines [d in Å(I)(hkl] are: 3.62(100)(075,0112,234,234), 3.42(45) (244, 244), 3.35(95)(0113), 3.23(65)(078), 3.01(45)(239, 239), 2.945(85)(088), 2.885(80), 1.916(45). The name parasterryite reflects its close structural relationship with sterryite. Sterryite is more abundant than parasterryite. Electron-microprobe analyses of two samples gave: 1) Sb-rich sterryite (wt.%): Cu 1.27(1), Ag 2.19(11), Hg 0.55(5), T1 0.56(8), Pb 44.76(25), Bi 0.26(7), Sb 24.71(11), As 5.33(9), S 20.47(11), total 100.10(39), and 2) Sb-poor sterryite: Cu 0.73(4), Ag 4.12(13), Pb 44.58(16), Sb 20.84(22), As 8.27( 12), S 20.92(7), total 99.47( 15). The unit cell of Sb-rich sterryite is: a 8.1891(1), b 28.5294( 13), c 42.98(2) Å, β 94.896(8)°, V = 10005(5) Å3 (space group P21/n). It presents a powder diagram close to that of sterryite from Madoc, Ontario, the type locality. The crystal structures of sterryite and parasterryite (not described here) are very similar, and represent a limiting case of homeotypy; they are also expanded homologues of owyheeite. The structural formula of parasterryite is based on 48 cations and 58 S, ideally Ag4Pb20(Sb 14.5As9.5)Σ24S58(z=4).The structural formula of sterryite is based on 47 cations and 56 S, with an (As-As)4+ dimer [d(As-As) = 2.64 Å] and a specific Cu site, ideally Cu(Ag,Cu) 3Pb19(Sb,As)22(As-As)S56 (Z=4). The presence of the As-As dimer in sterryite indicates its formation with a lower. f(S2) than parasterryite, which may also explain the formation of some rare Pb-Sb-As sulfosalts at Madoc

Synthesis, structural determination and magnetic properties of layered hybrid organic-inorganic, iron (II) propylphosphonate, Fe[(CH3(CH2)(2)PO3)(H2O)], and iron (II) octadecylphosphonate, Fe[(CH3(CH2)(17)PO3)(H2O)]

International audienceFe[(CH3(CH2)2PO3)(H2O)] (1) and Fe[(CH3(CH2)17PO3)(H2O)] (2) were synthesized by reaction of FeCl2·6H2O and the relevant phosphonic acid in water in presence of urea and under inert atmosphere. The compounds were characterized by elemental and thermogravimetric analyses, UV visible and IR spectroscopy. The crystal structure of (1) was determined from X-ray single crystal diffraction studies at room temperature: monoclinic symmetry, space group P21, a=5.707(1)Å, b=4.811(1)Å, c=11.818(2)Å, and β=98.62(3)°. The compound is lamellar and the structure is hybrid, made of alternating inorganic and organic layers along the c direction. The inorganic layers consist of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from the water molecule, separated by bi-layers of propyl groups. A preliminary structure characterization of compound (2) suggests a similar layered structure, but with an interlayer spacing of 40.3 Å. The magnetic properties of the compounds were both studied by a dc and ac SQUID magnetometer. Fe[(CH3(CH2)2PO3)(H2O)] (1) obeys the Curie Weiss law at temperatures above 50 K (C=3.81cmKmol, θ=-62K), indicating a Fe +II oxidation state, a high-spin d6 (S=2) electronic configuration and an antiferromagnetic exchange couplings between the near-neighbouring Fe(II) ions. Below T=22K, Fe[(CH3(CH2)2PO3)(H2O)] exhibits a weak ferromagnetism. The critical temperature of T=22K has been determined by ac magnetic susceptibility measurements. Compound (2) shows the same paramagnetic behaviour of the iron (II) propyl derivative. The values of C and θ were found to be 3.8cmKmol and ‑44 K, respectively, thus suggesting the presence of Fe +II ion in the S=2 spin state and antiferromagnetic interactions between Fe(II) ions at low temperatures. Zero-field and field cooled magnetic susceptibility vs. T plots do not overlap below T=30K, suggesting the presence of an ordered magnetic state. The critical temperature, T, has been located by the peaks at T=26K from the ac susceptibility (χ′and χ″) vs. T plots. Below T hysteresis loops recorded in the temperature region 1