C-axis Josephson Tunneling Between YBCO and Pb: Direct Evidence for Mixed Order Parameter Symmetry in a High-T_c Superconductor

We report a new class of $c$-axis Josephson tunneling experiments in which a conventional superconductor (Pb) is deposited across a single twin boundary of a YBa_2Cu_3O_{7-\delta} crystal. We measure the critical current as a function of magnitude and angle of magnetic field applied in the plane of the junction. In all samples, we observe a clear experimental signature of an order parameter phase shift across the twin boundary. These results provide strong evidence for mixed $d$- and $s$-wave pairing in YBCO, with a reversal in the sign of the $s$-wave component across the twin boundary.Comment: 4 pages RevTex, 4 postscript figures included, submitted to Phys. Rev. Let

A mossbauer study of phonon and electron anomalies in perovskite superconductor La₁.₈₅Sr.₁₅Cu.₉₅Sn.₀₅O₄

Temperature-dependent Mossbauer measurements have been carried out on the high T[sub c] oxide superconductor (La₁.₈₅Sr₀.₁₅) CuO₄ (T[sub c] = 37 K) doped with tin. Using the 23.88 keV Mossbauer resonance at ¹¹⁹Sn, the valency state of tin ions in the superconductor has been characterized and hyperfine interactions studied. The temperature dependence of the mean-squared displacement shows phonon softening near 75 and 170 K. Above 180 K the data fit to a harmonic model with 0[sub D] ~ 403K; between 77 and 160 K, 0[sub D] = 383K; and below 77 K, 0[sub D] is temperature dependent. Below 250 K, the temperature dependence of the shift indicates that, in addition to a temperature dependent 0[sub D], there are electronic changes characteristic of a phase transformation. The valency of tin is found to be 4+.M.S. (Master of Science

Evidence of Biorealistic Synaptic Behavior in Diffusive Li-based Two-terminal Resistive Switching Devices

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Binary and analog resistive switching in LiCoO2-based, two-terminal, devices driven by reversible Li-ion migration

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Aerial Oxidation of a VIV-Iminopyridine Hydroquinonate Complex: A Trap for the VIV-Semiquinonate Radical Intermediate

The reaction of 2,5-bis[N,N′-bis(2-pyridyl-aminomethyl)aminomethyl]-p-hydroquinone (H2bpymah) with VO2+ salts in acetonitrile or water at a low pH (2.2-3.5) results in the isolation of [{VIV(O)(Cl)}2(μ-bpymah)], the p-semiquinonate complex [{VIV(O)(Cl)}2(μ-bpymas)](OH), the cyclic mixed-valent hexanuclear compound [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3, and [(VVO2)2(μ-bpymah)]. [{VIV(O)(Cl)}2(μ-bpymas)](OH) is an intermediate of the radical-mediated oxidation of [{VIV(O)(Cl)}2(μ-bpymah)] from O2. At lower pH values (2.2), a reversible intramolecular electron transfer from the metal to the ligand of [{VIV(O)(Cl)}2(μ-bpymas)](OH) is induced with the concurrent substitution of chlorine atoms by the oxygen-bridging atoms, resulting in the formation of [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3. The metal complexes were fully characterized by X-ray crystallography, infrared (IR) spectroscopy, and magnetic measurements in the solid state, as well as by conductivity measurements, UV-vis spectroscopy, and electrochemical measurements in solution. The oxidation states of the metal ions and ligands were determined by the crystallographic data. The [{VIV(O)(Cl)}2(μ-bpymah)]-[{VIV(O)(Cl)}2(μ-bpymas)](OH) redox process is electrochemically reversible. The VIV ion in the semiquinonate compound exhibits a surprisingly low oxophilicity, resulting in the stabilization of OH- counterions at acidic pH values. An investigation of the mechanism of this reaction reveals that these complexes induce the reduction of O2 to H2O2, mimicking the activity of enzymes incorporating two redox-active centers (metal-organic) in the active site

Growth and transport properties of HT-LixCoO2 thin films deposited by pulsed laser deposition

International audienceThe successful in situ growth of single phase, c-axis oriented, layered structured LixCoO2 thin films on (0 0 0 1) Al2O3 substrates by pulsed laser deposition is reported. Thin films were grown in an oxygen pressure of 1 mbar and substrate temperatures varying from 300 up to 600 °C. It is found that the surface roughness and electrical resistance of the films depends strongly on the deposition temperatures

Resistive switching phenomena in HT-LixCoO2 thin films deposited by PLD

LGEP 2012 ID = 1035International audienc

Send Orders for Reprints to [email protected] Mn III 2 Ln III 2 (Ln = Gd, Dy, Ho) Complexes From The Initial Employment of 1,3-Propanediol In Mixed 3d/4f Metal Cluster Chemistry

Abstract: The initial employment of 1,3-propanediol (pdH 2 ) in the synthesis of 3d/4f metal clusters has afforded a new family of tetranuclear [Mn 2 Ln 2 O 2 {(CH 3 ) 3 CCO 2 } 8 {(CH 3 ) 3 CCO 2 H} 2 (pdH 2 ) 2 ] (Ln = Dy, 1; Gd, 2; Ho, 3) complexes. Compounds 1-3 represent new additions to the small family of Mn III 2 Ln 2 clusters possessing planar or diamond-like cores. Variable-temperature, dc and ac magnetization measurements were performed on compounds 1-3 and revealed the existence of very weak antiferromagnetic exchange interactions between the metal centers leading to a ground state spin value S = 5 in case of 2·2(CH 3 ) 3 CCO 2 H·2H 2 O

Synthesis, structure, magnetic properties and aqueous solution characterization of p-hydroquinone and phenol iminodiacetate copper(ii) complexes

The reaction of Cu2+ acetate monohydrate with 2-[N,N′-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H 4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H 4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl] hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 . The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discusse