Temperature dependence of electron properties of Sn doped nanobelts

This paper reports on the measurements of transport properties of high crystalline quality Sn doped In₂O₃ nanobelts. The samples presented metallic conduction in a large range of temperatures; however, at low temperatures, the resistivity showed a slight increase and the current–voltage curves showed a tendency to saturate even in the low-voltage range. From these observations, we discuss some arguments on the possibility of low dimensional conducting channels as the main responsible for the conduction at low temperatures. Additionally, we present an alternative technique for production of low resistance ohmic contacts, which can be further used in devices’ construction.     

Possible manifestation of spin fluctuations in the temperature behavior of the resistivity of Sm<Subscript>1.85</Subscript>Ce<Subscript>0.15</Subscript>CuO<Subscript>4</Subscript> thin films

A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm_1.85Ce_0.15CuO₄ thin films around T _sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm³⁺ moments with the energy ħω_sf = k _B T _sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρ_res, electron-phonon ρ_e-ph(T) = AT, and electron-electron ρ_e-e(T) = BT ² contributions in addition to the fluctuation-induced contribution ρ_sf(T) due to thermal broadening effects (of the width ω_sf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi energy are estimated as ω_p = 2.1 meV, τ ₀ ⁻¹ = 9.5 × 10⁻¹⁴ s⁻¹, λ = 1.2, and E _F = 0.2 eV, respectively. The text was submitted by the authors in English.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Structural characterization and Curie temperature determination of a sodium strontium niobate ferroelectric nanostructured powder

The Curie temperature and its correlation with the magnitude of the displacement of the niobium atom from the center of [NbO₆] octahedra in NaSr₂Nb₅O₁₅ nanostructured powder were investigated. A single powder was prepared by high-energy ball milling. A powder with an average crystallite size of 37 nm was prepared by calcining the precursor at 1423 K. The refinement of the structural parameters was carried out by the Rietveld method. NaSr₂Nb₅O₁₅ exhibits tetragonal symmetry with the tungsten bronze structure (a=b=12.3495 (6) Å, c=3.8911 (2) Å, V=593.432 (5) Å³, and Z=2). The site occupancy of the Na⁺ and Sr²⁺ cations and the interatomic distances between the niobium and oxygen atoms were derived. The [NbO₆] octahedron undergoes both rotation and tilting depending on the crystallographic site. The Curie temperature of the powder was derived using both the impedance and infrared spectroscopy methods.     

Effect of quantum entanglement on Aharonov-Bohm oscillations, spin-polarized transport and current magnification effect

We present a simple model of transmission across a metallic mesoscopic ring. In one of its arm an electron interacts with a single magnetic impurity via an exchange coupling. We show that entanglement between electron and spin impurity states leads to reduction of Aharonov-Bohm oscillations in the transmission coefficient. The spin-conductance is asymmetric in the flux reversal as opposed to the two-probe electrical conductance which is symmetric. In the same model, in contradiction to the naive expectation of a current magnification effect, we observe enhancement as well as suppression of this effect depending on the system parameters. The limitations of this model to the general notion of dephasing or decoherence in quantum systems are pointed out.     

The crystal and molecular structure of diaquadichlorotheophyllinecopper(II)

Summary The crystal structure of CuCl₂(C₇H₈N₄O₂)(H₂O)₂ has been determined from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R=0.067 for 2123 observed reflections. Unit cell constants are:a=9.930(8),b=9.987(8),c=7.483(6) Å,=123.2(1),=94.5(1),= 83.9(1)°. The space group is P¯1 withZ=2. The structure consists of diaquadichlorotheophyllinecopper(II) complexes linked by hydrogen bonds. The coordination polyhedron of copper is a square pyramid whose base, severely tetrahedrally distorted, is formed by a water molecule [Cu-Ow=2.025(7) Å], two chlorines [Cu-Cl=2.273(4), 2.296(4) Å] and an imidazole nitrogen [Cu-N=1.983(9) Å] from the theophylline ligand. A second water molecule is at the apex of the pyramid [Cu-Ow=2.292(7) Å]. Coordination is completed to a distorted octahedral one by a long Cu ... O=3.164(7) Å contact involving the exocyclic oxygen at C₆ of the theophylline ligand.     

X-ray crystal structure of the copper(II)bis(2,2′-dipyridyl)dithiocarbamate,produced by an unusual reaction of CS2 with Cu−N bonds

The title compound was obtained from a CS₂ solution of bis(2,2-dipyridylamido)copper(II), by insertion of solvent into this complex. In the structure of the dithiocarbamate the metal atom is approximately square-planar coordinated by four S atoms from two chelating ligands. Considering the long interactions between the metal center and the S(2) atom from a centrosymmetrically related complex [Cu(1)...S(2)=3.230 Å], double bridged dimers are formed with the copper atoms in an elongated square-pyramidal coordination. The crystals are monoclinic, space groupP2 ₁/n witha=14.549(3),b=11.662(3)c=15.329(4) Å and =114.79(2)°.     

Eigenvalue Asymptotics of the Stokes Operator for Fractal Domains

The leading asymptotic term for the function that counts theeigenvalues of the Stokes operator is determined for fairlygeneral underlying bounded domains. Moreover, the remainderis estimated in terms of the fractality of the boundary of thedomain. The results obtained resemble corresponding ones forthe Dirichlet Laplacian. 1991 Mathematics Subject Classification:35P20.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.