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Dive into the research topics where Uri Dai is active.

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Featured researches published by Uri Dai.


Applied Physics Letters | 1988

Preparation and patterning of YBaCuO thin films obtained by sequential deposition of CuOx/Y2O3/BaF2

Nir Hess; Leandro R. Tessler; Uri Dai; G. Deutscher

Superconducting thin films of YBaCuO were prepared by stacking layers of CuOx , Y2O3, and BaF2 onto substrates held at room temperature. The CuOx layer was obtained by oxidizing in air a previously deposited metallic Cu film. After deposition of the subsequent layers, the films were annealed at 880 °C in flowing oxygen. Samples 1 μm thick on sapphire showed an onset at Tonsetc =85 K and zero resistance at T0c =70 K; on yttria‐stabilized zirconia (YSZ), Tonsetc =90 K and T0c =80 K. Patterned films are easily obtained by applying conventional photolithographic methods to the Cu film.


Applied Physics Letters | 1990

Strong magnetic field dependence of the critical currents correlated to the microstructure of YBaCuO ceramics

Uri Dai; G. Deutscher; Claude Lacour; Francine Laher-Lacour; Philippe Mocaër; Michel Lagues

Critical currents of YBaCuO ceramics were measured at 77 K by transport measurements in an applied magnetic field H. A hysteretic behavior between 10 and 10 000 G was observed. For decreasing fields, the critical current Jc obeys a power law H−n with n ranging between 0.6 and 2.8. The exponent n is correlated with the microstructure and the average grain size of the ceramic. This power law behavior is discussed in terms of modified flux creep and flux flow regimes related to the microstructure.


Applied Physics Letters | 1987

Critical current of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ in strong applied fields

Uri Dai; G. Deutscher; Ralph Rosenbaum

Critical currents of the new high‐temperature superconductor Y1Ba2Cu3O7 have been measured in applied fields of up to 7 T and for temperatures down to 70 K. We find that the critical current is drastically reduced by the application of magnetic fields much smaller than the upper critical field of the samples, Hc2. This anomalous behavior might be due to very weak pinning, or to a very strong anisotropy of Hc2. Hc2 is found to follow a linear temperature dependence that however extrapolates to a critical temperature higher than that measured directly. This might result from the existence of a percolative structure, or from the presence of a small volume fraction of high critical temperature, high critical field regions.


Applied Physics Letters | 1987

Critical current of Y1Ba2Cu3O7 in strong applied fields

Uri Dai; G. Deutscher; Ralph Rosenbaum

Critical currents of the new high‐temperature superconductor Y1Ba2Cu3O7 have been measured in applied fields of up to 7 T and for temperatures down to 70 K. We find that the critical current is drastically reduced by the application of magnetic fields much smaller than the upper critical field of the samples, Hc2. This anomalous behavior might be due to very weak pinning, or to a very strong anisotropy of Hc2. Hc2 is found to follow a linear temperature dependence that however extrapolates to a critical temperature higher than that measured directly. This might result from the existence of a percolative structure, or from the presence of a small volume fraction of high critical temperature, high critical field regions.


Applied Physics Letters | 1990

Cathodoluminescence study of thin films of high Tc superconductors

Z. Barkay; Jacob Azoulay; Y. Lereah; Uri Dai; Nir Hess; D. Racah; E. Grünbaum; G. Deutscher

Cathodoluminescence (CL) of thin films of high Tc superconductors was studied in the scanning electron microscope. The depth and the lateral locations of the different phases can be revealed. In thin films, unlike the bulk superconductors, the CL information can be obtained either from the film itself or the substrate by varying the primary beam energy. At high beam energy, substrate defects and slight thickness variations of a single high Tc phase are observed. The resolution of the CL measurements improves at low temperatures.


Applied Physics Letters | 1989

Flux‐creep‐limited critical currents in YBa2Cu3O7−δ ceramics

Uri Dai; Nir Hess; Leandro R. Tessler; G. Deutscher; Geneviève Vetter; Francine Queyroux; Nicole Bontemps; Roger Mahoum; Michel Lagues; Philippe Mocaër

Critical currents of YBa2Cu3O7−δ bulk‐sintered samples were measured at and above 77 K in the presence of magnetic fields. In moderate magnetic fields a H−n dependence with n<1 was observed. Transport measurements give n≂0.5, indicating that critical currents are limited by flux creep rather than by field quenching of Josephson junctions.


Physica C-superconductivity and Its Applications | 1993

Long coherence lengths in c-axis oriented Y0.6Pr0.4Ba2Cu3O7 thin films determined by the resistive transitions under applied magnetic fields

D. Racah; Uri Dai; G. Deutscher

Abstract We report the measurement and analysis of the resistive transitions under applied magnetic fields for c axis oriented thin films of Y 0.6 Pr 0.4 Ba 2 Cu3O7 (PYBCO). We estimate the in-plane and out-of-plane coherence lengths to be much larger YBCO. Our data could not be fitted in a satisfactory way to the ‘giant flux-creep’ model. We also discuss the change in the superconducting properties of this system as compared to YBCO in terms of the double pair-breaking theory (both for magnetic impurities and magnetic field) and find it to be insufficient to explain the observed data. We discuss the large coherence lengths ξab ξc in PYBCO in terms of the van-Hove scenario for HTC.


Journal of Physics D | 1988

Contacts of very low resistivity to YBaCuO thin films

Leandro R. Tessler; Uri Dai; Nir Hess; G. Deutscher

The authors report a method for the preparation of contacts of very low surface resistivity (contact resistance multiplied by contact area) to polycrystalline YBaCuO thin films. The method provides contacts with resistivities smaller than 3*10-7 Omega cm2, which are obtained by the application of silver paint dots onto the film surface prior to annealing. Only one annealing procedure is required for the preparation of samples and contacts. Above the critical current both the four-terminal and two-terminal resistances obeyed Ohms law for several current decades.


Physica C-superconductivity and Its Applications | 1993

Electrochemical room temperature reduction and reoxydation of thin films and pellets of YBa2Cu3O7−x

Yosef Scolnik; M. L. Rappaport; Nir Hass; Uri Dai; David Cahen

Abstract YBa 2 Cu 3 O 7 (1237) was reduced and reoxydated quantitatively, in a controlled manner, at room temperature (RT), by way of extraction or insertion of oxygen, using an electrochemical set-up. RT reduction and reoxygenation of thin films, which led to homogeneous products, as judged by X ray diffraction. Since reduction leads to loss of superconductivity and re-oxidation restores it, this method allows room temperature control over superconducting properties of (parts of) films. This permits patterning of (1237) thin films. SNS-like structures were already prepared by this method. The method affords control not only over n(E F ) via [oxygen] bulk , but also over the quality of the intergranular contact, possibly via control of [oxygen] in the outermost layers of grains (in films and pellets).


Review of Scientific Instruments | 1991

Hall voltage measurements using ac lock‐in detection

Leandro R. Tessler; Meir Nissim; Uri Dai; Ralph Rosenbaum

The measurement of the Hall constant in insulating highly resistive films is a difficult and challenging task. Owing to the small currents that may be passed through the insulating films, the Hall voltages are often very small in magnitude. A simple electronic circuit using commercial lock‐in amplifiers is described which allows measuring these minute Hall voltages. Other practical measuring suggestions are also presented.

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Claude Lacour

Centre national de la recherche scientifique

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Francine Laher-Lacour

Centre national de la recherche scientifique

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M. Laguës

Centre national de la recherche scientifique

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Philippe Mocaër

Centre national de la recherche scientifique

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Michel Lagues

École Normale Supérieure

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