High-temperature Superconductor YBa2Cu3O7 Research Articles

Modification and nano-patterning of high-Tc superconducting thin films by masked ion beam irradiation

Ion irradiation of the high-temperature superconductor (HTS) YBa2Cu3O7 (Y-123) creates different types of defects depending on ion mass, energy and dose. Irradiation with helium ions of moderate energy (75 keV) primarily creates point defects. We measure in situ the modification of electrical transport properties of Y-123 thin films (thickness 310 nm) during ion irradiation. The He ions penetrate thin films and produce collision cascades with small lateral straggle that allow for patterning of nanostructures in the HTS layer. We present features smaller than 100 nm in size produced by masked ion beam irradiation of Y-123 films. Computer simulations indicate that nano-patterning of Y-123 thin films with 10 nm lateral resolution is achievable.

Magnetic properties and atomic structure of La2/3Ca1/3MnO3–YBa2Cu3O7 heterointerfaces

A heterostructure comprised of a 2.7 nm (7 unit cell) thick layer of the metallic ferromagnet La2/3Ca1/3MnO3 and two 50 nm thick layers of the high-temperature superconductor YBa2Cu3O7 epitaxially grown on (100) SrTiO3 by pulsed-laser deposition was characterized by magnetization measurements and spherical-aberration-corrected high-resolution transmission electron microscopy (HRTEM). The saturation magnetization is about half of that in bulk La2/3Ca1/3MnO3. A massive reduction in the magnetization previously inferred from sputter-deposited La2/3Ca1/3MnO3–YBa2Cu3O7 heterostructures can be ruled out. HRTEM image analysis, combined with image simulation and a focus series reconstruction, revealed atomically sharp epitaxial structures with stacking sequences –(La,Ca)O–CuO2– and –BaO–MnO– at the top and bottom interface.

Imaging of the power distribution of a circular oversized waveguide with a Josephsoncantilever at 762 GHz

The transmission of FIR (far-infrared) radiation with a Gaussian intensity profile throughoversized hollow metal waveguides and a quasi-optic HDPE lens system has beenstudied to determine the optimal conditions for analysis of THz antennas. Wepresent applications of our scanning THz electronics prober STEP. As a scanningsensor we employ a Josephson junction from the high-temperature superconductorYBa2Cu3O7 on a vibrating cantileverprepared from a LaAlO3 bicrystal. This superconducting detector is cooled to a temperature of about 50 K by acryocooler and the waveguides under investigation stay at room temperature. Based on thisset-up in a vacuum chamber we investigate the microwave power density at 762 GHz withhigh spatial resolution far below the corresponding wavelengths. Measurements have shownthat the multimodal radiation distribution in an oversized waveguide is not favorable forthe analysis of THz antennas.

Magnetic-Field-Enhanced Incommensurate Magnetic Order in the Underdoped High-Temperature SuperconductorYBa2Cu3O6.45

We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa2Cu3O6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift in the magnetic-excitation spectrum. A reconstruction of the Fermi surface driven by the field-enhanced magnetic superstructure may thus be responsible for the unusual Fermi surface topology revealed by recent quantum-oscillation experiments.

Mechanism of thermal decomposition of the nonstoichiometric compound YBa2Cu3O6.8

Thermal decomposition of the nonstoichiometric high-temperature superconductor YBa2Cu3O6.8 at a temperature of 200°C in air has been investigated using the full-profile analysis of X-ray diffraction lines. Two mechanisms of decomposition are revealed. The first mechanism, i.e., separation into two phases with a different oxygen content, occurs continuously. The second mechanism, i.e., disordering of the heavy atoms Y, Ba, Ba, Y along the crystallographic axis c, begins to occur after a 20- to 35-h annealing and progresses with a further annealing.

Strength of the spin-fluctuation-mediated pairing interaction in a high-temperature superconductor

Theories based on the coupling between spin fluctuations and fermionic quasiparticles are among the leading contenders to explain the origin of high-temperature superconductivity, but estimates of the strength of this interaction differ widely1. Here, we analyse the charge- and spin-excitation spectra determined by angle-resolved photoemission and inelastic neutron scattering, respectively, on the same crystals of the high-temperature superconductor YBa2Cu3O6.6. We show that a self-consistent description of both spectra can be obtained by adjusting a single parameter, the spin–fermion coupling constant. In particular, we find a quantitative link between two spectral features that have been established as universal for the cuprates, namely high-energy spin excitations2,3,4,5,6,7 and ‘kinks’ in the fermionic band dispersions along the nodal direction8,9,10,11,12. The superconducting transition temperature computed with this coupling constant exceeds 150 K, demonstrating that spin fluctuations have sufficient strength to mediate high-temperature superconductivity.

Dislocation description of twins in high-temperature superconductor YBa2Cu3O7−δ

The thin twins theory is consistently applied to the dislocation description of twins in the high-temperature superconductor YBa2Cu3O7−δ (YBCO). Quantitative analysis of the twin shape shows agreement with a theoretical analysis and gives a new method of evaluating the twin boundary energy γtw. The friction stress Sfr acting on a twinning dislocation is also determined. The formation of a twin and twin microstructures are analyzed. The principles of microstructure design by twinning in YBCO crystals for enhanced Jc at high magnetic fields are discussed.

Coherent Raman spectroscopy of YBa_2Cu_3O_7

We report preliminary results on the optical driving and spectroscopic detection of Raman-active features in thin films of the high-temperature superconductor YBa(2)Cu(3)O(7) in its normal phase by means of coherent Stokes and anti-Stokes Raman scattering, in a reflection geometry. Reference measurements on germanium are also reported. We observe phonon resonances which interfere coherently with a broad electronic resonance centered at zero frequency, giving rise to characteristic asymmetric spectral features. Our measurements provide a first step towards applying nonlinear optical wave-mixing spectroscopy to correlated electron systems.

Vibrational spectrum and structural features of the high-temperature superconductor YBa2Cu3O7

The structure of YBa2Cu3O7 has been represented as consisting of molecular ions CuO22− and described in space group P4m2. This structure provides a satisfactory interpretation of IR-and Raman-active bands. The calculated isotope shifts of the bands induced by the substitution of 18O for 16O are well consistent with the measured shifts. A possible mechanism of the motion of electron pairs is suggested.

Raman Study of Tb-doped YBCO and Ce-doped GdBCO

The phase formation and the variation of the normal phonon frequencies of high temperature superconductors YBa2Cu3O7−δ and GdBa2Cu3O7−δ upon doping Tb and Ce for Y and Gd, respectively, have been investigated using XRD and Raman spectroscopy measurements. It is found that the increase of doping content causes the formation of impurity phases that can be detected in the XRD and Raman spectra, and results in the suppression of superconductivity. Moreover, analysis of the Raman peaks reveals that substitutions of Tb and Ce for Y and Gd in the parent structure are restricted to low concentrations in favor of impurity island formation.

Josephson Network as a Model for Inhomogeneous Superconductor: a Microwave Power Absorption

We discuss the applied magnetic field dependence of the microwave absorption by a three-dimensional array of up to 30 × 30 × 30 Josephson junctions with random parameters including the resistivity, capacity, and inductance of each junction. The numerical simulation results for the networks show characteristic microwave absorption anomalies observed in the ceramic samples of high temperature superconductor YBa2Cu3O7−x. We also provide a discussion of the absorption in simple analytical terms of the Josephson loop instabilities.

Frequency dependence of the nonlinear response in YBa2Cu3O7−x transmission lines

The authors evaluate the frequency dependence of the nonlinear response in high-temperature superconductor YBa2Cu3O7−x thin films by simultaneously measuring the nonlinear intermodulation products and harmonic generation in broadband superconducting transmission lines at 76K. The frequencies of the two-tone incident signal are set to produce spurious signals from 1to21GHz. They extract a nonlinear term ∣ΔR2+jωΔL2∣ by applying a model of spurious signal generation in superconducting transmission lines to their measurement results. They found that this nonlinear term follows a linear dependence on frequency, indicating a dominant contribution of the nonlinear inductance ΔL2 over the nonlinear resistance ΔR2, (ωΔL2⪢ΔR2), for the superconducting nonlinear response.

Microwave and Terahertz Surface Resistance of MgB2 Thin Films

The knowledge of the surface resistance Rs of superconducting thin film at microwave and terahertz (THz) regions is significant to design, make and assess superconducting microwave and THz electronic devices. In this paper we reported the Rs of MgB2 films at microwave and THz measured with sapphire resonator technique and the time-domain THz spectroscopy, respectively. Some interesting results are revealed in the following: (1) A clear correlation is found between Rs and normal-state resistivity right above Tc, ρ0, i.e., Rs decreases almost linearly with the decrease of ρ0. (2) A low residual Rs ,l ess than 50µ� at 18 GHz is achieved by different deposition techniques. In addition, between 10 and 14 K, MgB2 has the lowest Rs compared with two other superconductors Nb3Sn and the high-temperature superconductor YBa2Cu3O7−δ(YBCO). (3) From THz measurement it is found that the Rs of MgB2 up to around 1 THz is lower than that of copper and YBCO at the temperature below 25 K. (4) The frequency dependence of Rs follows ω n ,w hereω is angular frequency, and n is power index. However, n changes from 1.9 at microwave to 1.5 at THz. The above results clearly give the evidences that MgB2 thin film, compared with other superconductors, is of advantage to make superconducting circuits working in the microwave and THz regions.

Formation of the magnetization loops of high‐Tc superconductors

AbstractWe have investigated the irreversibility magnetic field and the critical current density of the high temperature superconductor YBa2Cu3O7–δ single crystal. Vibrating sample magnetometer (V.S.M.) method was used for these measurements. Magnetization hysteresis loops scale and shape are strongly dependent on the temperature values and the angle θ between the direction of the applied magnetic field and c‐axis. For the large single crystals at very low temperature the loops present several flux jumps “saw‐tooth” and we observe the second peak “fish‐tail” for high temperature values but not with applied magnetic field perpendicular to the ab ‐planes. Beyond θ = 30°, the irreversibility field Hirr increases deviates from different temperature values. The variation of the critical current density Jc with applied magnetic field parallel to c‐axis for different temperatures was studied. Here, Jc is an effective critical current density deduced from the measured magnetization by the Bean formula. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of an external magnetic field and a trapped magnetic flux on the current-voltage characteristics of a granular high-temperature superconductor YBa2Cu3O7−δ

A comparative study of the current-voltage characteristics of the high-temperature ceramic superconductor YBa2Cu3O∼6.95 at T = 77.3 K is performed over wide ranges of external magnetic fields H ext and “treatment” fields H treat. It is found that the field dependences of the parameters a and j c involved in the exponential equation E = a(j − j c)v describing the current-voltage characteristics depend substantially on the method used for applying the magnetic field, whereas the exponent v ∼ 2 depends on neither the method of application nor on the magnetic field strength. The field dependence of the trapped magnetic field H trap is determined.

Room temperature near-field microwave imaging with an YBa2Cu3O7 Josephson cantilever

Josephson junctions from the high-temperature superconductor YBa2Cu3O7 operated in a temperature range of 40–80K cooled by a cryocooler can be deployed on a cantilever to detect microwave radiation. The spatial scanning step width used here is 15μm with operating distance of the cooled Josephson cantilever to the surface of the device under test (DUT) of about 150μm. The DUT is operated at room temperature. Due to the realization as an active cantilever a topographic image of the DUT as well as the microwave power distribution can be obtained.

Magnetism at the interface between ferromagnetic and superconducting oxides

Carefully controlled interfaces between two materials can give rise to novel physical phenomena and functionalities not exhibited by either of the constituent materials alone. Modern synthesis methods have yielded high-quality heterostructures of oxide materials with competing order parameters. Although magnetic correlations at the interface are expected to be important in determining the macroscopic properties of such systems, a quantitative determination of the interfacial magnetization profile has thus far not been reported. Here we examine superlattices composed of the half-metallic ferromagnet La2/3Ca1/3MnO3 and the high-temperature superconductor YBa2Cu3O7 by absorption spectroscopy with circularly polarized X-rays and by off-specular neutron reflectometry. The resulting data yield microscopic insight into the interplay of spin and orbital degrees of freedom at the interface. The experiments also reveal an extensive rearrangement of the magnetic domain structure at the superconducting transition temperature. This methodology establishes an incisive probe of the interplay between competing electronic order parameters in oxide heterostructures.

Reversible and irreversible magnetocaloric effect in theNdBa2Cu3O7 superconductor in relation to specific heat and magnetization

A recently developed technique for measuring the isothermal magnetocaloric coefficient(MT) is applied to the studyof a superconducting NdBa2Cu3O7 single crystal. Results are compared with magnetization(M) and specific heat(C). In the reversibleregion both C and MT follow the scaling law of the 3D-xy universality class. Theanomalies connected with flux-line lattice melting are visible onMT(B) curves as peaks andsteps, similar to C(T) curves yet with much smaller background. At lower temperature, in the irreversible region theMT(B) behaviour resemblesmore that of M(B), exhibiting the ‘fishtail’ effect. Our results confirm that the peculiaritiesof the phase diagram known from the high-temperature superconductorYBa2Cu3O7, e.g. vortex melting, dominance of critical fluctuations and absence of aBc2 critical field line, are a common property of RE-123 systems.

Evolution of the specific-heat anomaly of the high-temperature superconductorYBa2Cu3O7 under the influence of doping through application of pressure up to 10 GPa

The evolution of the specific-heat anomaly in the overdopedrange of a single crystal of the high-temperature superconductorYBa2Cu3O7 has been studied under the influence of pressure up to 10 GPa, using AC calorimetry in aBridgman-type pressure cell. We show that the specific-heat jump as well as the bulkTc are reduced with increasing pressure in accordance with a simple charge-transfer model.This new method enables us through pressure-induced charge transfer to study the dopingdependence of the superconducting transition, as well as the evolution of thesuperconducting condensation energy on a single stoichiometric sample without addingatomic disorder.

Thermal degradation of poly(acrylic acid) containing metal nitrates and the formation of YBa2Cu3O7−x

AbstractThe use of polymers containing metal salts as ceramic high‐temperature superconductor (HTSC) precursors may provide a relatively simple and rapid method for producing materials that can take advantage of advanced polymer processing and then be pyrolyzed to HTSCs. The mechanisms of thermal degradation in these precursors, which have not been characterized, can be used to optimize the pyrolysis conditions for HTSC production. This article describes the degradation of a precursor based on poly(acrylic acid) (PAAc) containing yttrium, barium, and copper nitrates in the proportions needed for the formation of the HTSC YBa2Cu3O7−x (YBCO). This article also describes the effects of the pyrolysis process on the resulting materials. The degradation of the precursor is a complex, multistage process. The presence of the metal ions and HNO3 reduces the thermal stability of PAAc and increases the degradation rate. The results indicate that the initial stages of the pyrolysis should be conducted in argon or nitrogen to inhibit BaCO3 formation and that the final stages should be conducted in air/oxygen to enhance oxidation. Optimization of the pyrolysis conditions produces a YBCO film with minimal contamination. © 2005 Wiley Periodicals, Inc. J PolymSci Part B: Polym Phys 43: 1168–1176, 2005