Showing papers on "High-temperature superconductivity published in 1999"
TL;DR: Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives.
Abstract: Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials.
304 citations
TL;DR: This work compares gap energies, measured by different experimental techniques, for the copper oxide superconductors and shows that these reveal the existence of two distinct energy scales: Δp and Δc, which, in the overdoped regime, converge to approximately the same value, as would be the case for a BCS superconductor where pairs form and condense simultaneously.
Abstract: The 'pseudogap' observed in the electron excitation spectrum of underdoped copper oxide superconductors has become the focus of considerable attention in the field of high-temperature superconductivity. In conventional superconductors, described by 'BCS' theory, an energy gap appears at the superconducting transition temperature (Tc); the pseudogap, in contrast, is observed well above Tc (ref. 1) and can be large compared to the conventional BCS gap. Here I compare gap energies, measured by different experimental techniques, for the copper oxide superconductors and show that these reveal the existence of two distinct energy scales: Δp and Δc. The first, determined either by angle-resolved photoemission spectroscopy or by tunnelling, is the single-particle excitation energy-the energy (per particle) required to split the paired charge-carriers that are required for superconductivity. The second energy scale is determined by Andreev reflection experiments, and I associate it with the coherence energy range of the superconducting state-the macroscopic quantum condensate of the paired charges. I find that, in the overdoped regime, Δp and Δc converge to approximately the same value, as would be the case for a BCS superconductor where pairs form and condense simultaneously. But in the underdoped regime, where the pseudogap is observed, the two values diverge and Δp is larger than Δc. Models that may provide a framework for understanding these results involve the existence of pairing above the condensation temperature, as might occur in a crossover from BCS to Bose-Einstein condensation behaviour or from the formation of striped phases.
291 citations
TL;DR: A detailed review of local magnetic probes is presented in this paper, including Lorentz, magnetic force microscopy, Bitter decoration, scanning Hall probe microscopy and magneto-optical imaging, and scanning superconducting quantum interference device microscopy.
Abstract: Investigations of the magnetic properties of high temperature superconductors (HTSs) have revealed the existence of striking new vortex phenomena due, in part, to their strong crystalline anisotropy, very short coherence lengths and the much larger thermal energies available at high temperatures Some of these phenomena, for example vortex lattice 'melting', pose serious problems for technological applications of the most anisotropic HTS materials and a fuller understanding of them is of considerable importance The most direct information regarding vortex structures and dynamics is obtained through local measurement of the magnetic field within or at the surface of a superconducting sample A detailed review of such local magnetic probes is presented here including Lorentz microscopy, magnetic force microscopy, Bitter decoration, scanning Hall probe microscopy, magneto-optical imaging, and scanning superconducting quantum interference device microscopy In each case the principles underpinning the techni
195 citations
TL;DR: In this paper, the authors reported the observation of microscopically coexisting ferromagnetism and superconductivity in a hybrid ruthenocuprate RuSr/sub 2/GdCu/Sub 2/O/sub 8/, with T/sub c/spl les/40 K.
Abstract: We report the observation of microscopically coexisting ferromagnetism and superconductivity in a hybrid ruthenocuprate RuSr/sub 2/GdCu/sub 2/O/sub 8/, with T/sub c//spl les/40 K. By means of various substituents it is established that the superconductivity originates in the CuO/sub 2/ planes and the ferromagnetism in the RuO/sub 2/ planes, as expected. Muon spin relaxation measurements show that the ferromagnetism, with Curie temperature T/sub M/=132 K, is microscopically uniform and originates from the entire sample bulk. This is probably the first confirmed example of uniform microscopic coexistence of superconductivity and atomic ferromagnetism. The material is determined from thermopower measurements to be an underdoped cuprate with a projected T/sub c,max/=90-100 K, typical of a two-layer cuprate. The oxygen isotope effect exponent of /spl alpha//sub Tc/=1.7 is the largest observed in the high-T/sub c/ cuprates. These materials are expected to provide a rich source of new physics and applications.
176 citations
TL;DR: The coupling strength inferred from results is sufficient to account for the high transition temperatures of the copper oxides, highlighting a prominent role for spin fluctuations in driving superconductivity in these materials.
Abstract: In conventional superconductors, the most direct evidence of the mechanism responsible for superconductivity comes from tunnelling experiments, which provide a clear picture of the underlying electron–phonon interactions1,2. As the coherence length in conventional superconductors is large, the tunnelling process probes several atomic layers into the bulk of the material; the observed structure in the current–voltage characteristics at the phonon energies gives1, through inversion of the Eliashberg equations, the electron–phonon spectral density α2F(ω). The situation is different for the high-temperature copper oxide superconductors, where the coherence length (particularly for c-axis tunnelling) can be very short. Because of this, methods such as optical spectroscopy and neutron scattering provide a better route for investigating the underlying mechanism, as they probe bulk properties. Accurate reflection measurements at infrared wavelengths and precise polarized neutron-scattering data are now available for a variety of the copper oxides3,4,5, and here we show that the conducting carriers (probed by infrared spectroscopy) are strongly coupled to a resonance structure in the spectrum of spin fluctuations (measured by neutron scattering). The coupling strength inferred from those results is sufficient to account for the high transition temperatures of the copper oxides, highlighting a prominent role for spin fluctuations in driving superconductivity in these materials.
153 citations
TL;DR: In this paper, phonon measurements for the YBa2Cu3O7-x high-temperature superconductors reveal the presence of charge fluctuations and the inferred periodicity is that expected if the charge is located in the domain walls separating spin stripes.
Abstract: Understanding the behaviour of the electrons in the high-temperature copper oxide superconductors remains a challenging problem An important class of models1,2,3,4,5 argues that the distribution of electronic charge and spin is not homogeneous: rather, spin and charge adopt a dynamic arrangement in which the spins on the copper form antiferromagnetic stripes, separated by domain walls containing the charge1,2,3,4,5 The dynamic behaviour of the spins has been extensively studied by neutron scattering, and recent results6 have shown that the low-frequency fluctuations for different classes of materials display a universal spatial behaviour that is consistent with the stripe picture But arguments for the existence of the stripe phases are difficult to sustain without a demonstration that charge is distributed in the domain walls Here we report phonon measurements for the YBa2Cu3O7-x high-temperature superconductors, which reveal the presence of charge fluctuations The inferred periodicity is that expected if the charge is located in the domain walls separating the spin stripes Our results therefore provide strong support for the existence of a dynamic stripe phase in the high-temperature superconductors
80 citations
Posted Content•
TL;DR: In this paper, the question of coexistence of superconductivity and ferromagnetism in the high temperature superconductor RuSr$_2$GdCu$_ 2$O$8-\delta$ using a field theoretical approach was addressed.
Abstract: In this paper we address the question of coexistence of superconductivity and ferromagnetism in the high temperature superconductor RuSr$_2$GdCu$_2$O$_{8-\delta}$. Using a field theoretical approach we study a one-fermion effective model of a ferromagnetic superconductor in which the quasiparticles responsible for the ferromagnetism form the Cooper pairs as well. We discuss the physical features which are different in this model and the standard BCS model and consider their experimental consequences.
70 citations
TL;DR: In this paper, the experimental trends in a database of specific heat measurements near T c in high magnetic fields for type-II superconductors with a large value of κ = λ/ξ, including mostly high-temperature supercondors, are considered.
Abstract: We consider the experimental trends in a database of specific heat measurements near T c in high magnetic fields for type-II superconductors with a large value of κ = λ/ξ, including mostly high-temperature superconductors. Whereas the BCS limiting case is well established in low-T c superconductors, the exact 3D-XY behavior illustrated by the λ-transition of 4 He applies only in the particular case of optimally doped YBa 2 Cu 3 O x . Otherwise, transitions are intermediate either between the BCS and the 3D-XY models (e.g., YBa 2 Cu 3 O 7.00 ), or between the 3D-XY model and the Bose-Einstein condensation (BEC) (e.g., Bi 2 Sr 2 CaCu 2 O 8 ). The key parameter in ordering this sequence appears to be the product k F ξ of the Fermi wave number by the coherence length, as evaluated from tunneling spectra in the vortex cores. Such a trend, which is consistent with theoretical descriptions of the strong coupling limit, is visible in the thermodynamics of the phase transition. Implications on the effective mass, the density of pairs just above T c , the pseudo-gap behavior, etc., are discussed.
56 citations
01 Jan 1999
TL;DR: In this article, the role of geometrical and surface barriers in high-temperature superconductors is investigated. And the effect of pinning sites on the Decay of the Orientational Order of a Vortex Lattice is examined.
Abstract: I: Flux Penetration And Pinning.- Vortex Pinning and Jc in High-Tc Superconductors: Advance from Understanding Toward Some Practical Issues.- Magnetic Flux Penetration Into the High-Temperature Superconductors.- Statics and Dynamics of the Flux-Line Lattice in Realistic Geometries.- Pinning Mechanisms in High-Tc Superconductors.- Microstructures and Critical Currents in High-Tc Superconductors.- Mechanical and Squid Measurements on Nb Thin Films: Learning from a Conventional Superconductor.- Flux Instabilities in Current-Carrying Type-II Superconductors.- Magneto-Optical Studies of Magnetization Processes in High-Tc Superconductors.- Experimental Evaluation of the Role of Geometrical and Surface Barriers in BSCCO-2212 Crystals.- Paul Flux Pinning in (RE) Ni2B2C Superconductors.- Scanning Squid Microscopy of Flux Distributions and Motion Near Surface Features in NbSe2.- Anisotropy Induced Crossover from Fractal to Non-Fractal Flux Penetration in High-Tc Thin Films.- Magnetic Flux Noise and Pinning in Low and High-Tc Superconducting Films.- Effect of Pinning Sites on the Decay of the Orientational Order of a Vortex Lattice.- Strong Pinning Mechanisms in High-Tc Superconducting YBa2Cu3O7-? Thin Films.- Influence of Columnar Defects on Critical Currents, Pinning Forces and Irreversibility Fields in (Tm1-xYx)Ba2Cu3O7 Single Crystals up to 50 T.- II: Vortex Dynamics.- Vortex Melting and the Liquid State in YBa2Cu30x.- Vortex Lattice and Dissipation Related Properties at High Frequency in Layered High Tc Superconductors.- The Susceptibility of the Vortex Lattice.- Statistical Mechanics of Vortex Lines.- Josephson Vortex Dynamics in Layered Structures.- High Resolution Specific Heat Experiments on the Vortex Melting Line in MBa2Cu3Ox (M=Y, Dy and Eu)Crystals: Observation of First- and Second-Order Transitions up to 16T.- On the Intermediate State and the Melting Transition in High-Tc BSCCO Single Crystal Superconductors.- Commensurability Oscillations and Smectic Vortex Phase Transition in YBa2Cu3Oy Single Crystals.- 19 F NMR Study of Vortex Lattice Evolution in Fluorinated YBCO System.- Evidence for Two Vortex Species in Niobium Films in Parallel Fields.- Vortex Lattice Melting Probed by Nernst Effect.- Emission of Radiation by Vortex Arrays Motion in DC Transformer.- Vortex Dynamics in Bulk HTS with Levitation Techniques.- Crossover From Pointlike to Linelike Vortex Creep in Superconducting Films with Columnar Defects.- What is the Vortex Lattice Melting, Reality or Fiction?.- III: General.- Extended Ginzburg-Landau Theory of HTS: The Coulping of the Superconducting to a Structural Phase Transition Strongly Enhances Tc.- Anisotropy and Transport Properties in Substituted and Intercalated High Temperature Superconductors Studied by Raman Spectroscopy.- Dynamics of the Phase Separation of LA 2CUO4+x Single Crystals.- Interpretation of the Non-Linear Inductive Response of Superconducting Films.- Magnetooptic Measurements of the Local AC Susceptibility in High-Temperature Superconductors in a Wide Frequency Range.- Plasmons in Nanotube Bundles.- IV: Applcations.- Applications of High Temperature Superconductors.
52 citations
TL;DR: In this paper, the authors discuss the possibility of a superconducting bulk magnet for a Maglev train and present a preliminary design of the bulk magnet and also melt processing for REBaCuO and LREBa-CuO bulk superconductors.
Abstract: One of the prospective applications of high critical temperature superconductors is a superconducting magnet for the magnetically levitated (Maglev) train. Development shows that RE (rare earth) BaCuO and LRE (light rare-earth) BaCuO superconductors prepared by melt processes have a high critical current density at 77 K and high magnetic fields. LRE-Ba-Cu-O bulk superconductors melt-processed in a reduced oxygen atmosphere, named oxygen-controlled-melt-growth (OCMG) process, are very promising for high field application as a superconducting permanent magnet with liquid nitrogen refrigeration. Compared to good quality melt-grown REBaCuO bulks, LREBaCuO bulks exhibit larger critical current densities in high magnetic fields and much improved irreversibility field at 77 K, implying that more effective flux pinning can be realized in a commercially feasible way. In this study, we discuss the possibility of a superconducting bulk magnet for a Maglev train. A preliminary design of the bulk magnet and also melt processing for REBaCuO and LREBaCuO bulk superconductors and their characteristic superconducting properties are presented.
47 citations
TL;DR: In this article, a compositional-controlled melt-processing technique in air and postannealing in Ar was used to construct high quality binary (Nd0.33Sm0.67)Ba2Cu3O7−δ monodomain superconductors.
Abstract: High-quality binary (Nd0.33Sm0.67)Ba2Cu3O7−δ monodomain superconductors were fabricated by the combination of a compositional-controlled melt-processing technique in air and postannealing in Ar. Critical current densities over the whole field range were observed strongly dependent on Ar postannealing while holding superconducting transition temperatures as high as 96 K. The suppressed chemical variation between the rare-earth element (RE: Nd, Sm) and Ba associated with disperse RE2BaCuOy (RE211) precipitate due to the decomposition occurring in Ar postannealing was attributed to the modified flux pinning. This makes Ar postannealing promising to process superconductors with desired properties for various applications.
TL;DR: In this article, the authors systematically investigated the influence of both pressure and intrisic effects on Tc in high-temperature superconductors and found that Tc is influenced not only by a pressure-induced increase in charge carrier density, but also by intisic effects in Tl0.5Pb 0.5Sr2Ca 1−xYxCu2O7.
Abstract: The pressure dependence of Tc in high-temperature superconductors is experimentally found to be influenced not only by a pressure-induced increase in charge carrier density but also by intrisic effects. The influence of both contributions was systematically investigated in Tl0.5Pb0.5Sr2Ca1−xYxCu2O7. The behavior of superconductors with three or four CuO2-layers is further complicated by the inequivalence of the inner and outer CuO2-layers. High-pressure experiments up to 46 GPa are analyzed in view of the above.
TL;DR: In this article, the effect of fluctuation induced conductivity (FIC) on polycrystalline superconductors was investigated and compared with the theoretically obtained values from the model proposed.
Abstract: We have investigated the fluctuation induced conductivity (FIC) of two high-Tc superconductors (HTSC) namely Bi2Sr2Ca1Cu2O8+δ and Y1−xCaxBa2Cu3Oy. The effective medium theory is used to formulate the Aslamazov–Larkin type equations for these polycrystalline superconductors. For the three dimensional case the temperature exponent remains unaltered since both the exponents for the ab plane and c direction FICs in the crystal are same. But the situation is more complex in the two dimensional case where the counterparts in the crystal have different temperature dependencies. The FIC is evaluated and compared with the theoretically obtained values from the model proposed. We have also evaluated the exponents, the coherence lengths, and the crossover temperature. The analysis based on the present model reveals that these two superconductors are similar concerning their nature of fluctuations. The extent of a particular fluctuation region of course differs from one HTSC to another.
TL;DR: In this paper, the magnetic relaxation rate was calculated for the vortex-glass or collective-creep model and the thermal activated model considering backward hopping, and it was found that the former models were in good agreement with the experiment at relatively low temperature regions, while the latter were at higher temperatures near Tc.
Book•
28 May 1999TL;DR: In this paper, the structure and electronic structure of cuprates are discussed. But the results from selected other techniques are not presented, as shown in Table 1 : Table 1.1.
Abstract: 1. Introduction 2. Structure and electronic structure of cuprates 3. Photoemission - theory 4. Photoemission - experimental 5. Examples 6. Early photoelectron studies of cuprates 7. Bi2212 and other Bi-cuprates 8. Y123 and related compounds 9. NCCO and other cuprates 10. Surface chemistry 11. New techniques in photoelectron spectroscopy 12. Results from selected other techniques.
TL;DR: In this paper, a three-dimensional numerical analysis of electromagnetic force characteristics in the mixed-magnet type mixed-spl mu/levitation system is carried out and the results of the analysis are compared with experiments.
Abstract: A permanent-magnet type mixed-/spl mu/ levitation system, which only needs an iron, permanent magnets and bulk superconductors, can realize an advantageous levitation system-for example, for transportation over a relatively long distance because of its simple structure and stable levitation without active control. A three-dimensional numerical analysis of electromagnetic force characteristics in the mixed-/spl mu/ levitation system is carried out and the results of the analysis are compared with experiments. From these results, the authors have confirmed that the three-dimensional structure of the magnetic field and the electromagnetic performance of superconductors strongly influence the characteristics of the electromagnetic force acting on the iron, which become unstable in some cases.
TL;DR: In this article, the case is made for solving the problem of extrinsic nonlinearity through the use of localized measurements of microwave surface impedance and electromagnetic fields, and a brief introduction is given to the work on scanning near-field microwave microscopy.
Abstract: This paper discusses some of the major experimental features of microwave nonlinearity in high temperature superconductors, both intrinsic and extrinsic. The case is made for solving the problem of extrinsic nonlinearity through the use of localized measurements of microwave surface impedance and electromagnetic fields. Along these lines, a brief introduction is given to our work on scanning near-field microwave microscopy.
TL;DR: In this article, the flux pinning behavior of ternary melt-processed (Nd-Eu-Gd)Ba2Cu3Oy superconductors is studied with varying defect concentrations using magnetotransport and magnetization measurements.
Abstract: The flux pinning behavior of ternary melt-processed (Nd–Eu–Gd)Ba2Cu3Oy superconductors is studied with varying defect concentrations using magnetotransport and magnetization measurements. A huge field-induced bump feature in the resistivity with increasing defect density, field-induced magnetization kink and linear voltage-current (V-I) characteristics over the whole transition temperature regime favor the phenomenon of vortex entanglement in the liquid phase. The Nd/Ba substitution sites along with the fine second-phase particles are one of the possible reasons for the vortex entanglement and these defects give rise to high critical current density and reduced dissipation at low temperature with significant enhancement in pinning.
01 Jan 1999
TL;DR: The physics of superconductivity and superfluidity, macroscopic quantum phenomena found in many conductors at low temperatures and in liquid helium 4 and helium 3, are described in this paper.
Abstract: This 1998 book describes the physics of superconductivity and superfluidity, macroscopic quantum phenomena found in many conductors at low temperatures and in liquid helium 4 and helium 3. In the first part of the book the author presents the mean field theory of generalized pair condensation. This is followed by a description of the properties of ordinary superconductors using BCS theory. The book then proceeds with expositions of strong coupling theory and the Ginzberg-Landau theory. The remarkable properties of superfluid helium 3 are then described, as an example of a superfluid with internal degrees of freedom. The topics covered are dealt with in a coherent manner, with all necessary theoretical background given. Recent topics in the field, such as the copper-oxide high temperature superconductors and exotic superconductivity of heavy fermion systems are discussed in the final chapter. This book will be of interest to graduate students and researchers in condensed matter physics, especially those working in superconductivity and superfluidity.
TL;DR: In this paper, the epitaxial thin films of the TI cuprate superconductors were studied with x-ray photoemission spectroscopy, and the results showed that the TI superconductor is a superconducting superconductor.
Abstract: Epitaxial thin films of the TI cuprate superconductors are studied with x-ray photoemission spectroscopy.
01 Jan 1999
TL;DR: In this paper, the authors reported the observation of superconductivity in the lanthanum copper oxides with transition temperatures up to 38K and the first discovery of YBa2Cu3O7) a superconducting material with a transition temperature of 92K.
Abstract: Perhaps one of the greatest discoveries of this century was the phenomenon of superconductivity. A Dutch physicist, Haike Kamerlingh Onnes at the University of Leiden first made this discovery in 1911 [1] when examining the current carrying properties of metallic mercury at low temperatures, with the aid of his newly acquired ability to liquify helium. Seventy five years later in 1986, two physicists J. George Bednorz and K. Alex Muller at the IBM research laboratory in Zurich, Switzerland discovered the first of a new class of High Temperature Superconductors (HTS) [2]. They reported the observation of superconductivity in the lanthanum copper oxides with transition temperatures up to 38K. The real excitement began less than one year later with the discovery of YBa2Cu3O7) a superconducting material with a transition temperature of 92K [3], well above the temperature of liquid nitrogen. This indicates the beginning of the era of high-temperature superconductivity. As a snowy ball rolls from the top of a hill, this achievement generated an enormous new interest in superconductivity, and as a result many new compounds have been synthesized since 1988. These include bismuth lead strontium calcium copper oxides with Tc ~ 105K [4], thallium barium calcium copper oxide with Tc=125K [5] and the mercury compounds [6] with an upper Tc=133K.
TL;DR: The search for a different type of pairing mechanism for the copper oxides is revealing that an excitation of the electrons themselves may provide the glue.
Abstract: An explanation of high-temperature superconductivity in the copper oxides has been more elusive than for conventional superconductivity -- in which crystal lattice vibrations help bind electrons into pairs. The search for a different type of pairing mechanism for the copper oxides is revealing that an excitation of the electrons themselves may provide the glue.
TL;DR: In this paper, the effects of Ag addition both on trapped field capability and mechanical properties of bulk RE-Ba-Cu-O (RE: Y, Sm) superconductors were studied.
Abstract: Bulk superconductors can function as quasi-permanents with generating magnetic fields much higher than those of conventional permanent magnets. However, a large electromagnetic force acts on such bulk superconductors, which sometimes leads to fracture. It is known that Ag addition is effective in improving the fracture toughness of bulk Y-Ba-Cu-O superconductors. Therefore, in this paper, we have studied the effects of Ag addition both on trapped field capability and mechanical properties of bulk RE-Ba-Cu-O (RE: Y, Sm) and have found that Ag addition is indeed effective in improving the mechanical properties of a large single-grain RE-Ba-Cu-O.
TL;DR: In this article, the photoelectron escape depth in the high-temperature superconductor Bi2212 was calculated by use of electron energy-loss spectroscopy data, and it was shown that the escape depth is only 3 Angstrom for photon energies typically used in angle-resolved photoemission measurements.
Abstract: We calculate the photoelectron escape depth in the high-temperature superconductor Bi2212 by use of electron energy-loss spectroscopy data. We find that the escape depth is only 3 Angstrom for photon energies typically used in angle-resolved photoemission measurements. We then use this to estimate the number of inelastic secondaries, and find this to be quite small near the Fermi energy. This implies that the large background seen near the Fermi energy in photoemission measurements is of some other origin. [S0163-1829(99)08017-0].
TL;DR: In this paper, the influence of bending of the electronic band structure on the superconducting and normal state transport characteristics of interfaces involving high-T/sub c/ superconductors is discussed.
Abstract: Influences of the predominant d(x/sup 2/-y/sup 2/)-symmetry of the order parameter and of bending of the electronic band structure on the superconducting and normal state transport characteristics of interfaces involving high-T/sub c/ superconductors are discussed. It will be shown that these generic properties of the high-T/sub c/ cuprates are important factors for many characteristic aspects of interfaces in these materials, such as the angular dependencies of the critical current density, the normal state resistivity and consequently the I/sub c/R/sub n/-product of grain boundaries, the comparatively large contact-resistances between superconductors and normal-metals, and the small values of the Stewart-McCumber parameter /spl beta//sub c/ leading to the overdamped current-voltage characteristics.
TL;DR: In this article, a unified theory to explain the sign reversal of the mixed-state Hall resistivity rho(xy) in both high-T (c) and low-T(c) superconductors was developed.
Abstract: Taking into account pinning, thermal fluctuations, and vortex-vortex interactions, we develop a unified theory to explain the sign reversal of the mixed-state Hall resistivity rho(xy) in both high-T(c) and low-T(c) superconductors. Molecular dynamics simulations show that besides the pinning forces, either the thermal fluctuations in the high-T(c) superconductors or the vortex-vortex interactions in the low-T(c) ones play an important role in the sign reversal of rho(xy). From a calculated phase diagram for vortex motion, we find that the abnormal Hall effect always occurs in the plastic flow state of vortices. [S0163-1829(99)11629-1].
TL;DR: In this paper, an angle-resolved high-resolution photoemission study of strongly overdoped Bi2Sr2CaCu2O8+x single crystals with T-c similar to 60 K was performed.
Abstract: We report results of an angle-resolved high-resolution photoemission study of strongly overdoped Bi2Sr2CaCu2O8+x single crystals with T-c similar to 60 K. We find a nonzero superconducting (SC) gap along all three high symmetry directions in the Brillouin zone, in contrast with a d-wave scenario of high temperature superconductivity. Our data indicate that both the maximum gap value and the gap anisotropy decrease with overdoping. (C) 1999 Elsevier Science B.V. All rights reserved.
TL;DR: A group of complex cubic perovskite oxides REBa2NbO6 (RE=La and Dy) have been synthesized and developed for their use as substrates for both YBa2Cu3O7-δ and Bi(2223) superconductors as discussed by the authors.
Abstract: A group of complex perovskite oxides REBa2NbO6 (RE=La and Dy) have been synthesized and developed for their use as substrates for both YBa2Cu3O7-δ and Bi(2223) superconductors. These materials have a complex cubic perovskite (A2BB′O6) structure with lattice constants,a=8·48−8·60 A. REBa2NbO6 did not show any phase transition in the temperature range 30–1300°C. The thermal expansion coefficient, thermal diffusivity and thermal conductivity values of REBa2NbO6 are favourable for their use as substrates for highT c superconductors. The dielectric constant and loss factor of REBa2NbO6 are in a range suitable for their use as substrates for microwave applications. Both YBa2Cu3O7-δ and Bi(2223) superconductors did not show any detectable chemical reaction with REBa2NbO6 even under extreme processing conditions. Dip coated YBa2Cu3O7-δ thick films on polycrystalline REBa2NbO6 substrate gave aT c(0) of 92 K and a current density of ∼1·1×104 A/cm2 and Bi(2223) thick film on polycrystalline REBa2NbO6 substrate gave aT c(0) of 110 K and a current density of ∼ 4×103 A/cm2 at 77 K and zero magnetic field. A laser ablated YBa2Cu3O7-δ thin film deposited on polycrystalline REBa2NbO6 substrate gave aT c(0) of 90 K and a current density of ∼5×105 A/cm2.