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Bruynseraede, Y., E. Osquiguil, M. Maenhoudt, B. Wuyts, G. Nieva, J. Guimpel, D. Lederman, and I. K. Schuller. "New Properties of Oxygen Depleted YBa2Cu3Ox Films." Proceedings of the II International Conference on Macroscopic Quantum Phenomena ICMQP-2 (1992): 253.
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Osquiguil, E., Z. X. Gao, M. Maenhoudt, B. Wuyts, S. Libbrecht, and Y. Bruynseraede. "YBa2Cu3Ox: A natural multilayer system with tunable anisotropy." Journal of Physics: Condensed Matter 5, no. 33 A (1993).
Abstract: The authors report on magnetoresistivity rho ab( theta ,H,T) measurements below Tc in YBa2Cu3Oxn films with differing oxygen content x. The observed variations in the angular and field dependence of rho ab with reduced x indicate a gradual dimensional crossover from an anisotropic 3D to a quasi-2D behaviour. The increasing anisotropy is related to a decrease of the coupling between the Cu2O2 bilayers when oxygen is removed from the Cu1Ox chain-planes.
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Nieva, G., E. Osquiguil, J. Guimpel, M. Maenhoudt, B. Wuyts, Y. Bruynseraede, M. B. Maple, and I. K. Schuller. "Photoinduced changes in the transport properties of oxygen-deficient YBa2Cu3Ox." Physical Review B 46, no. 21 (1992): 14249–14252.
Abstract: We show that illumination of oxygen-deficient metallic YBa2Cu3Ox films produces a change in the Hall coefficient, an increase in the critical temperature, and a decrease in the electrical resistivity. These changes relax to equilibrium with characteristic times of the order of days, and are due to variations in both the carrier density and mobility. The relaxation times are of the same order of magnitude as the ones measured in nonilluminated oxygen-deficient films immediately after quenching.
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Wuyts, B., E. Osquiguil, M. Maenhoudt, S. Libbrecht, Z. X. Gao, and Y. Bruynseraede. "Influence of the oxygen content on the normal-state Hall angle in YBa2Cu3Oxn films." Physical Review B 47, no. 9 (1993): 5512–5515.
Abstract: We report on measurements of in-plane resistivity ?ab(T) and Hall coefficient RH(T) in c-axis-oriented oxygen-deficient YBa2Cu3Oxn thin films. Independent of the changes induced in RH(T) and ?ab(T) by the oxygen depletion, a quadratic temperature dependence is observed for the Hall angle ?H. The slope of cot?H versus T2 decreases as the oxygen content xn is reduced and saturates in the Tc(xn)=60 K plateau region. The results are discussed in the framework of the two-dimensional Luttinger liquid theory as proposed by Anderson.
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Osquiguil, E., M. Maenhoudt, B. Wuyts, Y. Bruynseraede, D. Lederman, and I. K. Schuller. "Photoexcitation and oxygen ordering in YBa2Cu3Ox films." Physical Review B 49, no. 5 (1994): 3675–3678.
Abstract: We report on the photoinduced enhancement of the critical temperature ?Tc and the in-plane conductivity ??ab measured in a c-axis-oriented YBa2Cu3Ox film as a function of oxygen concentration (6.4?x?7). Both ?Tc and ??ab decrease with the oxygen content, display a plateaulike behavior for 6.6?x?6.75, and become zero at x=7. This dependence of ?Tc on x is similar to that observed for the Tc enhancement due to ordering effects in oxygen-deficient YBa2Cu3Ox single crystals. We propose that the persistent photoinduced changes in YBa2Cu3Ox films are due to photoassisted oxygen ordering.
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Nieva, G., E. Osquiguil, J. Guimpel, M. Maenhoudt, B. Wuyts, Y. Bruynseraede, M. B. Maple, and I. K. Schuller. "Photoinduced enhancement of superconductivity." Applied Physics Letters 60, no. 17 (1992): 2159–2161.
Abstract: We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa 2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak-link devices with in situ tunable superconducting characteristics.
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Osquiguil, E., M. Maenhoudt, B. Wuyts, and Y. Bruynseraede. "Controlled preparation of oxygen deficient YBa2Cu 3Ox films." Applied Physics Letters 60, no. 13 (1992): 1627–1629.
Abstract: We describe a simple method based on the oxygen pressure-temperature phase diagram to prepare oxygen deficient YBa2Cu3Ox thin films. Systematic critical temperature and x-ray diffraction experiments clearly show that films with different oxygen contents (6.6?x?7) are obtained in a controlled, reproducible, and reversible way.
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Gao, Z. X., E. Osquiguil, M. Maenhoudt, B. Wuyts, S. Libbrecht, and Y. Bruynseraede. "3D-2D dimensional crossover in YBa2Cu3O7 films." Physical Review Letters 71, no. 19 (1993): 3210–3213.
Abstract: We show that, in fully oxidized YBa2Cu3O7 c-axis oriented films, the changes induced in the angular and field dependence of the magnetoresistivity ?ab by increasing the temperature towards Tc are similar to those caused by a lowering in oxygen content. This remarkable behavior can be interpreted as due to a crossover from a three-dimensional to a two-dimensional system as T approaches Tc. Moreover, our critical current data mimic the behavior observed by Qi Li et al. in YBa2Cu3O7/(PrxY1-x)Ba2Cu3O7 multilayers, suggesting the possibility that chain planes are superconducting.
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Osquiguil, E., M. Maenhoudt, B. Wuyts, Y. Bruynseraede, D. Lederman, G. Nieva, J. Guimpel, and I. K. Schuller. "Photoexcitation effects in YBa2Cu3Ox." Journal of Alloys and Compounds 195, no. C (1993): 667–670.
Abstract: We show through photoexcitation experiments carried out on YBa2Cu3Ox c-axis oriented films that photoinduced phenomena are not restricted to insulating samples. Superconducting films with critical temperatures varying between 2 K and 40 K show a clear enhancement of the superconducting transition after illumination. The increase in Tc is accompanied by a corresponding decrease in the resistivity ?, and an increase in the Hall coefficient RH, indicative of an increased carrier density. Furthermore, the carrier mobility is also affected by illumination.
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Vanacken, J., S. Libbrecht, M. Maenhoudt, C. Van Haesendonck, E. Osquiguil, and Y. Bruynseraede. "The magnetic moment relaxation in oxygen-deficient YBa2Cu3Ox." Physica C: Superconductivity and its applications 197, no. 1-2 (1992): 9–14.
Abstract: The magnetic moment relaxation in polycrystalline YBa2Cu3Oxmaterial has been studied using zero-field-cooled measurements. The temperature dependence of the relaxation rate shows a field-dependent maximum. When the oxygen content is reduced, the maximum shifts towards lower temperatures. This shift is directly related to a decrease of the intragrain critical current density in the oxygen-deficient material, inducing a decrease of the field H* for complete flux penetration. The characteristic activation energies for depinning in the oxygen-deficient material are below 20 meV.
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