Y Jaccard

Origin of Cu‐rich precipitate formation on superconducting films: A competition between nucleation, oxidation, and growth kinetics

We have unraveled the growth mechanism of Cu‐rich precipitates on the surface of c‐axis‐oriented DyBa2Cu3O7 thin films. Despite the strong oxidation conditions present, the surface of c‐axis DyBa2Cu3O7 acts as an ideal nucleation site for Cu2O crystallites, whose (110) planes are parallel to the substrate surface. Once nucleated, they act as effective sinks for the rest of the deposited copper and form large crystals that revert to monoclinic CuO upon cooling. This result has important implications for all currently used thin film growth processes and indicates that smooth surfaces can only be prepared under stringent composition control.

Electrochemical oxidation of La2CuO4 thin films grown by molecular beam epitaxy

Thin insulating and c-axis oriented films of La2CuO4 are grown using a molecular beam epitaxy technique. Subsequently, these films are oxidized electrochemically using a 1N KOH solution. This approach is used to induce superconductivity, leading to a maximum Tc0 of 31 K,, measured both resistively and inductively. The surface morphology, lattice constants and the resistivity before and after the electrochemical treatment are compared.

Dynamical conductivity of an MBE-grown La1.84Sr0.16CuO4 thin film at frequencies from 5 to 36 cm(-1)

We present the first wide-band (5–400 cm−1) measurements of the dynamical conductivity and the dielectric permittivity spectra of La2−xSrxCuO4 (x ≈ 0.16). A narrow Drude-like band is observed in the spectra, which is consistent with a d-wave pairing state. We determine the plasma frequency, scattering rate, and mean free path of the unpaired charge carriers responsible for this band. For the first time, “coherence peak”-like behavior is observed in the temperature dependence of the submillimeter conductivity of La2−xSrxCuO4, associated with the temperature evolution of the band in the superconducting state.

Anomalous millimeter-wave absorption in the superconducting phase of La2−xSrxCuO4

Direct measurements of the complex conductivity spectra of thin-film La2−2xSrxCuO4 are made at frequencies of 5–40 cm−1. Narrow, intense Drude-type excitation is observed in the superconducting phase.

Characterization of MBE-grown ultrathin films in the La2-xSrxCuO4±δ system

Using a molecular beam epitaxy deposition technique, c-axis La2-xSrxCuO4+/- (delta ) ultrathin films have been prepared on (001) SrTiO3 substrates. Several superconductive properties such as the critical temperature Tc, the penetration depth (lambda) ab(0), the activation energy for flux flow (Delta) U and the Hall coefficient RH are reported for the same set of films. As the dopant content is increased, maximum values for Tc and (Delta) U are observed near the optimum doping while RH decreases continuously.

Transmission electron microscopy investigations of defects in molecular beam epitaxy-grown oxide films

Abstract With a view to increasing the superconductive transition temperature of thin films of La 2 CuO 4 grown by molecular beam epitaxy, films were grown on substrates of lattice parameters such that the film-substrate misfit became small and tensile, or compressive. The microstructure of these films was investigated using transmission electron microscopy and qualitative correlations with physical properties suggested.

3D-XY critical behavior in La2−xSrxCuO4 thin films probed by penetration depth measurement

We sketch the evidence for anisotropic 3D-XY critical behavior in La2−xSrxCuO4 thin films and explore the implications of this scenario, supplemented by the experimental phase transition line.

La2−xSrxCuO4 thin films and multilayers prepared by MBE

We report on the realization of La2−xSrxCuO4/La2−ySryCuO4 multilayers and on a study of the superconducting transitions in magnetic field parallel and perpendicular to the c-axis. Measuring the activation energies for thermally activated flux flow, which give information on the correlation volume involved in flux jumps, allows to make an estimate of the interdiffusion at the interfaces.

Strontium concentration dependence of the in-plane penetration depth of superconducting La2−xSrxCuO4±δ very thin films☆

Using a Molecular Beam Epitaxy deposition technique, c-axis oriented La2−xSrxCuO4±δ thin films (50nm thick) were prepared 001) SrTiO3 substrates. Measurements of the acsheet impedance Z = R + iωLk performed with a two coil mutual inductance technique were used to determine the temperature dependent in-plane penetration depth λab(T) of the layers for various values of their Sr content x. Values of λab(0) deduced from the kinetic inductance Lk(T) and from the vortex pinning activation energy ΔU show an increase of λab(0) with growing carrier density n in the overdoped regime in sharp contrast with the simple Londons prediction λab−2(0) ∼ n.

The problem of Sr doping and interface abruptness in La2−xSrxCuO4 multilayers; the application of transmission electron microscopy

Abstract This represents an attempt to use the local investigative properties of transmission electron microscopy to examine the content and distribution of strontium in La 2− x Sr x CuO 4 thin films grown by molecular beam epitaxy on (001) strontium titanate substrates.