0000000000073246
AUTHOR
J.c. Martinez
showing 11 related works from this author
Temperature and magnetic-field dependence of quantum creep in various high-Tcsuperconductors
1999
To investigate the quantum tunneling of almost macroscopic vortex segments we measured the normalized relaxation rate Q of superconducting currents for various high-T{sub c} superconductors (HTS's) down to 100 mK in magnetic fields up to 7 T. At fields below {approx_equal}0.5 T, Q is essentially independent of T in the temperature regime between thermally activated and quantum motion as theoretically expected. However, at higher fields, we find an unexpected linear T dependence of Q persisting down to the lowest temperatures in all investigated samples. Since these compounds were chosen to represent the distinct classes of dirty and clean HTS's, the extrapolated Q(T=0) values are used to di…
Relation between microstructure and transport properties of epitaxial YBa2Cu3O7-d thin films.
1997
Abstract In order to understand the origin of the high critical current densities observed in thin superconducting films compared to single crystals we measured in several epitaxial YBa 2 Cu 3 O 7−δ thin films the magnetic field and temperature dependence of the superconducting current density j s and the dynamical relaxation rate Q ≡ d ln j s / d ln( d B/ dt ). For all samples we found that (i) the superconducting current density j s is independent of magnetic field up to a certain field B Φ . The value of this field, which is sample dependent, decreases with increasing temperature; (ii) for fields B>B Φ , the superconducting current density falls off as B −1/2 over several decades; (iii) …
Ferroelectricity and structure of BaTiO grown on YBa Cu O thin films
2000
We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O \(_{7 - \delta }\) as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O \(_{7 - \delta }\) and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction. The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indica…
Ferroelectric Properties and Crystal Structure of YBa2Cu3O7/BaxSr(1−x)TiO3 Heterostructures
1997
ABSTRACTEpitaxial YBa2Cu3O7/Ba0.5Sr0.5TiO3 (YBCO/BST) and YBCO/BaTiO3 (BTO) heterostructures were prepared by dc and rf sputtering on SrTiO3 and MgO substrates. The YBCO/BTO bilayers exhibit an inductive superconducting transition temperature of 85 K and the ferroelectric phase transition of BST shows a Curie-Weiss temperature of 310 K. Microstructure was investigated by x-ray-diffraction and atomic force microscopy. In this work we also studied the insulator's conductivity and the contribution of domain walls to permittivity.
Investigations on the c-axis transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-δ//PrBa/sub 2/Cu/sub 3/O/sub 7-δ/ thin film superlattices
1997
In this paper we report on the c-axis transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superlattices. We describe the preparation, characterisation and patterning of thin film superlattices into suitable mesa structures via standard photolithography. Resistive measurements were carried out which point towards an inhomogenous current distribution in the normal state resistance. Below T/sub c/, the c-axis properties determine the temperature dependent resistance. Resonant tunneling is observed with no Josephson current.
Fast and compact data acquisition for gas-filled detectors with delay line
2004
This article describes the functionality, implementation and performance of a PCI data acquisition board that can be used in conjunction with gas-filled detectors with delay line readout. The board combines a large on-board 256-MByte histogramming memory with a maximum 10-MHz count rate in continuous operation and integrates the time frame generation, histogram building and buffering functionalities in a single PCI board, resulting in a fast, compact and cost-effective data acquisition solution for the Spanish beamline BM16 at ESRF.
Influence of micro-structure in the low temperature critical currents of YBa2Cu3O7?? thin films
1996
Epitaxial YBa2Cu3O7−δ films nucleate in c-axis oriented single-crystalline islands. The surface of the single-crystalline SrTiO3 substrates exhibit steps of one third of the YBa2Cu3O7−δ c-axis. These steps generate a mismatch in the island boundaries between the CuO2 superconducting blocks. We show that these defect regions are strong candidates for being the pinning centers responsible for the large critical currents observed in Laser Ablated and Sputtered thin films.
Origin of high critical currents in YBa2Cu3O7−δ superconducting thin films
1999
Thin films of the high-temperature superconductor YBa2Cu3O7−δ exhibit both a large critical current (the superconducting current density generally lies between 1011 and 1012 A m−2 at 4.2 K in zero magnetic field) and a decrease in such currents with magnetic field that point to the importance of strong vortex pinning along extended defects1,2. But it has hitherto been unclear which types of defect—dislocations, grain boundaries, surface corrugations and anti-phase boundaries—are responsible. Here we make use of a sequential etching technique to address this question. We find that both edge and screw dislocations, which can be mapped quantitatively by this technique, are the linear defects t…
Josephson junctions and superconducting field effect transistors based on epitaxial Bi2Sr2Can-1CunO2(n+2) thin films
1998
Abstract Josephson junctions based on thin films of the Bi2Sr2Ca2Cu3O10+δ compound show IcRn products compatible with YBa2Cu3O7−δ samples. Using quasiparticle tunneling experiments we found evidence for a superconductor–insulator–superconductor tunneling process via localized states in the barrier. The Bi2Sr2CaCu2O8+δ compound is investigated regarding possible applications in superconducting field effect devices. We present thin films of four unit cells thickness that are superconducting at 58 K. An inverted metal–insulator–superconductor structure was prepared. From the modulation of the normal state resistance we estimate a carrier density of 7×1019 cm−3 for a superconducting sample. The…
Perpendicular transport properties of YBa_2Cu_3O_{7-\delta}/PrBa_2Cu_3O_{7-\delta} superlattices
2000
The coupling between the superconducting planes of YBa2Cu3O{7-\delta}/ PrBa2Cu3O{7-\delta} superlattices has been measured by c-axis transport. We show that only by changing the thickness of the superconducting YBa2Cu3O{7-\delta} layers, it is possible to switch between quasi-particle and Josephson tunneling. From our data we deduce a low temperature c-axis coherence length of 0.27 nm.
Critical currents and micro-structure in YBa2Cu3O7−δ thin films
1996
In an attempt to clarify the origin of the large critical current densitiesJ c observed in Laser Ablated and Sputtered YBa2Cu3O7−δ (YBCO) thin films, we make a systematic study of the low temperatureJ c in samples carefully analysed using STM and AFM.J c (B) is determined from torque-magnetometry performed in ring-patterned thin films. Epitaxial YBCO films nucleate in c-axis oriented single-crystalline islands with sizes ranging between 200 and 700 nm. We show thatJ c can be mainly explained by vortex pinning localised in the island boundaries.