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Reduction in the field-dependent microwave surface resistance inYBa2Cu3O7-delta with submicrometric BaZrO3 inclusions as a function of BaZrO3 concentration

2011-12-22T13:34:56Z

Reduction in the field-dependent microwave surface resistance inYBa2Cu3O7-delta with submicrometric BaZrO3 inclusions as a function of BaZrO3 concentration Pompeo, Nicola; Rogai, Raffaella; Augieri, A.; Galluzzi, V.; Celentano, G.; Silva, Enrico 2009-01-15 Journal of applied physics 105 013927-013927-7 In order to study the vortex pinning determined by artificiallyintroduced pinning centers in the small-vortex displacement regime, wemeasured the microwave surface impedance at 47.7 GHz in the mixed stateof YBa2Cu3O7-delta thin films, where submicrometric BaZrO3 particleshave been incorporated. As a function of the BaZrO3 content, weobserved that the absolute losses slightly decrease up to a BaZrO3content of 5%, and then increase. We found that themagnetic-field-induced losses behave differently in that they are notmonotonic with increasing BaZrO3 concentration. At small concentration(2.5%) the field-induced losses increase, but large reduction in thelosses themselves, by factors up to 3, is observed upon furtherincreasing the BaZrO3 concentration in the target up to 7%. Usingmeasurements of both surface resistance and surface reactance, weestimate vortex pinning-related parameters. We found that BaZrO3inclusions introduce deep and steep pinning wells. In particular, theminimum height of the energy barrier for single vortices is raised. Atlarger BaZrO3 content (5% and 7%) the phenomenon is at its maximum, butit is unclear whether it shows a saturation or not, leaving room forfurther improvements. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3056179]

Effect of BaZrO3 Inclusions on the Microwave Surface Impedance of YBCOFilms in a Magnetic Field

2011-12-22T13:34:56Z

Effect of BaZrO3 Inclusions on the Microwave Surface Impedance of YBCOFilms in a Magnetic Field Pompeo, Nicola; Rogai, Raffaella; Galluzzi, Valentina; Augieri, Andrea; Celentano, Giuseppe; Ciontea, Lelia; Petrisor, Traian; Silva, Enrico 2009-07-15 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 19 2917-2920 We perform measurements of high-frequency (similar to 48 GHz) microwavesurface impedance with an applied magnetic field in YBa2Cu3O7-delta (YBCO) laser-ablated films with various amounts of BaZrO3 ( BZO)sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusionsare very effective in the reduction of the field-induced surfaceresistance in our experimentally accessible field range [ 0, 0.8] T. Attemperatures low enough, the application of a moderate (similar to 0.2T) field makes the YBCO/BZO films markedly less dissipative than pureYBCO. This result, examined in the light of the very high measuringfrequency ( very small vortex oscillation amplitude) shows that BZOinclusions are even more effective pinning centers than columnardefects. We study the dependence of the vortex parameters ( vortexviscosity, pinning constant) on the BZO concentration. We examine thecorrelation between the reduction of the microwave dissipation and theareal density of BZO-induced defects. We argue that the very improvedperformances in a magnetic field are due to individual pinning ofvortices on BZO inclusions.

Transport Property Improvement by Means of BZO Inclusions in PLD GrownYBCO Thin Films

2011-12-22T13:34:56Z

Transport Property Improvement by Means of BZO Inclusions in PLD GrownYBCO Thin Films Augieri, Andrea; Galluzzi, Valentina; Celentano, Giuseppe; Angrisani, Achille Armenio; Mancini, Antonella; Rufoloni, Alessandro; Vannozzi, Angelo; Silva, Enrico; Pompeo, Nicola; Petrisor, Traian; Ciontea, Lelia; Gambardella, Umberto; Rubanov, Sergey 2009-06-05 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 19 3399-3402 A detailed study on YBa2Cu3O7-delta (YBCO) films with BaZrO3 (BZO)inclusions (YBCO-BZO) deposited on SrTiO3 substrate with different BZOcontents is presented. X ray diffraction, SEM imaging andsuperconductive critical temperature (T-c) measurements were performedto evaluate film growth quality. Independently from the BZO content,all YBCO-BZO films showed T-c values close to that of pure YBCOindicating that the T-c reduction which is usually observed on YBCO-BZOfilms can be successfully recovered by changing the depositionconditions. All YBCO-BZO films showed an improved critical currentdensity (J(c)) dependence on magnetic field if compared to the typicalJ(c)(H) of YBCO, resulting in higher irreversibility fields up to 9 Tat 77 K. SEM observation on etched samples suggests a direct linkbetween the defect density measured in YBCO-BZO samples and thatcalculated from the observed in field performances. The analysis ofJ(c)(B) as a function of applied magnetic field direction revealed thatthe pinning due to isotropic pinning centers typical for YBCO iscoupled with a c-axis correlated pinning in YBCO-BZO which can beascribed to BZO induced columnar defects. J(c)(B) recorded at severaltemperatures down to 10 K revealed matching effect features.

Nonlinear c-axis transport in Bi2Sr2CaCu2O8+delta from two-barrier tunneling

2011-12-22T13:34:56Z

Nonlinear c-axis transport in Bi2Sr2CaCu2O8+delta from two-barrier tunneling Giura, Maurizio; Pompeo, Nicola; Silva, Enrico 2009-04-01 Physical Review B 79 144504 Motivated by the peculiar features observed through intrinsic tunneling spectroscopy of Bi2Sr2CaCu2O8+delta mesas in the normal state, we have extended the normal-state two-barrier model for the c-axis transport [M. Giura , Phys. Rev. B 68, 134505 (2003)] to the analysis of dI/dV curves. We have found that the purely normal-state model reproduces all the following experimental features: (a) the parabolic V dependence of dI/dV in the high-T region (above the conventional pseudogap temperature), (b) the emergence and the nearly voltage-independent position of the "humps" from this parabolic behavior by lowering the temperature, and (c) the crossing of the absolute dI/dV curves at a characteristic voltage V-x. Our findings indicate that conventional tunneling can be at the origin of most of the uncommon features of the c-axis transport in Bi2Sr2CaCu2O8+delta. We have compared our calculations to experimental data taken in severely underdoped and slightly underdoped Bi2Sr2CaCu2O8+delta small mesas. We have found good agreement between the data and the calculations, without any shift of the calculated dI/dV on the vertical scale. In particular, in the normal state (above T-*) simple tunneling reproduces the experimentaldI/dV quantitatively. Below T-* quantitative discrepancies are limited to a simple rescaling of the voltage in the theoretical curves by a factor similar to 2. The need for such modifications remains an open question, that might be connected to a change of the charge of a fraction of the carriers across the pseudogap opening.