Showing papers on "High-temperature superconductivity published in 1990"
TL;DR: In this paper, a model for high T c superconductors was proposed by using the self-consistent renormalization theory and the electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state were calculated.
Abstract: Spin fluctuations in antiferromagnetic and nearly antiferromagnetic two dimensional (square lattice) itinerant electron systems, as a possible model for high T c superconductors, are investigated by using the self-consistent renormalization theory. The electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state are calculated. The results in the nearly antiferromagnetic regime as applied to high T c oxides seem to explain the experimental results both in their temperature dependence and in their orders of magnitudes. By using the same spin fluctuations we discuss superconductivity due to the spin fluctuation mechanism within a weak coupling theory. The order parameter is shown to have B 1 g or A 2 g symmetry and the critical temperature is evaluated to be of the right order of magnitude.
450 citations
TL;DR: In this article, the voltage-current characteristics of YBa2Cu3O7−δ epitaxial films within the flux creep model were described in a manner consistent with the resistive transition behavior.
Abstract: We describe the voltage‐current characteristics of YBa2Cu3O7−δ epitaxial films within the flux creep model in a manner consistent with the resistive transition behavior. The magnitude of the activation energy, and its temperature and magnetic field dependences, are readily derived from the experimentally observed power law characteristics and show a (1−T/Tc)3/2 type of behavior near Tc. The activation energy is a nonlinear function of the current density and it enables the determination of the shape of the flux line potential well.
331 citations
TL;DR: The current relaxation law in the regime of single-vortex pinning is obtained and the theory of pinning in the presence of thermal fluctuations is developed.
Abstract: Thermal fluctuations of vortex lines are shown to be capable of strongly reducing the value of the critical current in the mixed state of high-${\mathit{T}}_{\mathit{c}}$ superconductors. The theory of pinning in the presence of thermal fluctuations is developed. The current relaxation law in the regime of single-vortex pinning is obtained.
229 citations
TL;DR: It is concluded that although intercell coupling may enhance {ital T}{sub {ital c}0}, it is necessary for superconductivity of single-cell-thick YBCO layers in PrBCO matrix.
Abstract: We have fabricated epitaxial, nonsymmetric M\ifmmode\times\else\texttimes\fi{}N superlattices in which ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ (YBCO) layers either M=1, 2, 3, 4, or 8 c-axis unit cells thick are separated by insulating ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ (PrBCO) layers N unit cells thick (N=1 to \ensuremath{\sim}16). The zero-resistance transition temperature, ${\mathit{T}}_{\mathit{c}0}$, initially decreases rapidly with increasing PrBCO thickness but saturates at ${\mathit{T}}_{\mathit{c}0}$\ensuremath{\sim}19 K or ${\mathit{T}}_{\mathit{c}0}$\ensuremath{\sim}54 K for 1- and 2-cell-thick YBCO layers, respectively. We conclude that although intercell coupling may enhance ${\mathit{T}}_{\mathit{c}0}$, it is necessary for superconductivity of single-cell-thick YBCO layers in PrBCO matrix.
219 citations
TL;DR: High-resolution angle-resolved photoelectron spectroscopic measurements were made of the Fermi edge of a single crystal of Bi{sub 2}Sr{ sub 2}CaCu{sub 3}O{sub 8} at 90 K along several directions in the Brillouin zone, finding the shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons.
Abstract: High-resolution angle-resolved photoelectron spectroscopic measurements were made of the Fermi edge of a single crystal of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} at 90 K along several directions in the Brillouin zone. The resultant Fermi-level crossings are consistent with local-density band calculations, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250 K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level the spectra show correlation effects in the form of an increased effective mass, but the essence of the single-particle band structure is retained. The shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons. The effective inverse photohole lifetime is linear in energy.
215 citations
TL;DR: In this article, the authors reported the successful synthesis and preliminary physical characterization of superconducting (La, Sr)2CaCu2O6, which is a uniquely simple double-layer superconductor.
Abstract: STARTING with the pioneering work of Bednorz and Muller1, many copper-oxide-based superconductors with high transition temperatures (Tc) have been discovered. All contain layers of copper-oxygen squares, pyramids or octahedra as their electronically active structural components2,3. One structure type, first reported for La2SrCu2O6 and La2CaCu2O6 (ref. 4), has stood as an enigma since the beginning of high-Tc research. This crystal structure4-7 (Fig. 1) is the least complex of all the structures with the double layers of copper oxide pyramids common to the compounds with highest Tc, yet despite considerable effort, both published8,9 and unpublished, it has not until now been made superconducting. Here we report the successful synthesis and preliminary physical characterization of superconducting (La, Sr)2CaCu2O6. The highest transition temperature observed is 60 K at the composition La1.6Sr0.4CaCu2O6. This is a uniquely simple double-layer superconductor, which, like its single-layer analogue (La, Sr)2CuO4, becomes superconducting through the introduction of carriers in an unambiguous manner—by straightforward atomic substitution without the intervention of charge reservoir layers with flexible valence states.
215 citations
TL;DR: In this article, the effect of thermal fluctuations on collective flux-pinning and creeps is investigated for thin-film superconductors and layers with weak Josephson coupling between the layers in a field normal to the layers and much less than B c2.
Abstract: The effect of thermal fluctuations on collective flux-pinning and creeps is investigated for thin-film superconductors and layered superconductors with weak Josephson coupling between the layers in a field normal to the layers and much less than B c2 . Temperature and field dependences of the critical current j c in a two-dimensional (2D) system are obtained. The activation barriers for 2D flux-creep are shown to grow infinitely as U ( j )∝ j -μ at j ⪡ j c , which is characteristics for the vortex-glass state. At very small currents this behaviour is cut off by the plastic motion of edge-dislocation pairs which are either induced by disorder or thermally created, leading to linear current-voltage behaviour inhibiting the existence of a vortex-glass state in 2D systems. The Josephson coupling in layered superconductors changes the dimensionality of the vortex lattice. It is shown that a sufficiently large field when the lattice constant a o becomes less than the characteristic length of the interlayer coupling a 0 r 3D =( R j a 0 ) 1 2 or B > B 2D =Ф 0 / R 2 J , ( R J =Г 1 2 s is the effective Josephson length, s is the interlayer spacing and Г= m z / m is the mass anisotropy), the fluctuations of the vortex lines become of 2D nature. This means in particular that 3D-lattice melting will take place at T = T m , T m is the dislocation-mediated melting temperature of a 2D vortex-lattice. The mixed state at B > B 2D is studied and the possibility of different regimes of pinning and creep is demonstrated. The crossover from 2D to 3D pinning is found when the pinning length R c exceeds r 3D . The crossover conditions are derived and displayed in a schematic phase diagram.
209 citations
TL;DR: A new experiment is proposed: Andreev scattering, i.e., scattering of low-energy normal quasiparticles off the spatially varying order parameter when the qu asiparticles approach a normal-metal--superconductor interface from the normal side.
Abstract: Three new classes of superconductors have been discovered in the past decade: the organic superconductors, the heavy-fermion superconductors, and the oxide superconductors. All of them show characteristic anomalies that point to the possibility that they are anisotropic superconductors with a directionally dependent (k-dependent) gap function that vanishes in points or lines on the Fermi surface. The problem to identify the symmetry type of an anisotropic superconductor has not found a satisfactory solution yet. Although a number of experiments have been proposed that allow one in principle to distinguish between different symmetry types, most of them are ambiguous because they do not couple to the order parameter directly. Here we propose a new experiment: Andreev scattering, i.e., scattering of low-energy normal quasiparticles off the spatially varying order parameter when the quasiparticles approach a normal-metal--superconductor interface from the normal side.The idea is investigated in detail for anisotropic even-parity superconductors. To describe the quasiparticle dynamics, the Bogoliubov--de Gennes equations for anisotropic superconductors are introduced and approximated by the Andreev equations. The nonideality of the interface is taken into account by an interface potential parametrized by a reflection coefficient. This leads to a boundary condition for the Andreev equations at the interface. The pair potential \ensuremath{\Delta}(k^,r), i.e., the directionally and space-dependent order parameter that occurs as a scattering potential in the Andreev equations, is determined self-consistently for various nonideal interfaces to d-wave superconductors. This is equivalent to solving the proximity effect for interfaces with a finite reflection coefficient, and it is done using the quasiclassical formalism. Once \ensuremath{\Delta}(k^,r) has been obtained, the Andreev equations are integrated numerically, and the k-dependent Andreev reflection and transmission coefficients as well as the corresponding conductivities are computed.The theory predicts a directional dependence of the conductivities from which the k dependence of the order parameter can be reconstructed. For this effect to be a useful tool, new experiments will have to be devised. A double-point-contact experiment is proposed for an experimental realization of the idea.
206 citations
TL;DR: Reversible flux penetration in uniaxial layered superconductors is studied, taking into account the possible trapping of vortex cores between layers to induce high intrinsic critical currents parallel to the layers.
Abstract: Reversible flux penetration in uniaxial layered superconductors is studied, taking into account the possible trapping of vortex cores between layers. This is found to induce high intrinsic critical currents parallel to the layers. In low and intermediate fields, the flux lines experience a lock-in transition towards the layer plane, as a function of the field direction or intensity. Application to anisotropic high-{Tc} materials is discussed.
202 citations
TL;DR: A model combining thermally activated motion of flux lines, viscous flux flow at high current density, and distribution of activation energies is shown to reproduce the characteristic features of current-voltage curves of high-{ital T}{sub {ital c}} superconductors.
Abstract: A model combining thermally activated motion of flux lines, viscous flux flow at high current density, and distribution of activation energies is shown to reproduce the characteristic features of current-voltage curves of high-${\mathit{T}}_{\mathit{c}}$ superconductors. In particular the recent data of Koch et al. and Zeldov et al. can be explained without invoking a continuous phase transition (freezing into a superconducting vortex-glass phase) or a logarithmic current dependence of the activation energy.
TL;DR: In this paper, a stage-1 iodine-intercalated high-transition-temperature (high-Tc) superconductor, IBi2Sr2CaCu2Oy, is presented.
Abstract: INTERCALATION compounds are formed by inserting guest atomic or molecular species between weakly bound (usually by van der Waals forces) slabs of host materials without changing the inner crystal structure of the individual slabs. The best-known examples of host materials are graphite and the transition metal dichalcogenides1. These compounds can be made with different stage index n, where n denotes the number of slabs between adjacent intercalated layers. Intercalation provides a unique, well controlled approach to changing the physical and electronic properties of host materials over a wide range1. If intercalation can be adopted in the layered high-transition-temperature (high-Tc) superconductors, it could lead to the ability to engineer their properties, with a view to investigating the mechanism responsible for high-Tc superconductivity, improving the superconducting properties of the pristine materials, and developing new high-Tc superconductors and superconducting devices. We report here the successful synthesis and preliminary physical characterization of a stage-1 iodine-intercalated high- Tc superconductor, IBi2Sr2CaCu2Oy.
TL;DR: In this article, a block layer is proposed to isolate each CuO2-sheet and control carrier density within the Cu-O plane, which can isolate each sheet and control the carrier density.
Abstract: Structures of layered copper oxide compounds and relating high-temperature superconductors are classified by using the concept of the block layer which can isolate each CuO2-sheet and control carrier density within the Cu-O plane. Particular emphasis is laid on the Cu-O network dependent physico-chemical properties which are entirely governed by ordering and combination of constituent block layers. By the new classification method, structures and carrier-doping characteristics are predicted for prospective but hitherto unknown CuO2-layered superconductors. Possible importance of the concept of the block layer is pointed out in epitaxial growth of superconducting structures.
IBM1
TL;DR: Inverse photoemission as discussed by the authors makes it possible to obtain the complete information about unoccupied electronic states by determining the full set of quantum numbers, which can be applied to semiconductors, insulators and high temperature superconductors.
TL;DR: In this paper, a review of existing data on the thermal conductivity of high-T====== c¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ c¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ superconductors is presented, including pristine polycrystalline high-t====== c¯¯ ceramics, single crystal specimens, and materials structurally modified by substitution or by radiation damage.
Abstract: This paper reviews existing data on the thermal conductivity of high-T
c
superconductors. Included are discussions of pristine polycrystalline high-T
c ceramics, single crystal specimens, and high-T
c
materials structurally modified by substitution or by radiation damage. The thermal conductivity of high-T
c
superconductors is compared with that of conventional superconductors, and dramatic differences are found between the two families. Mechanisms of thermal conductivity applicable to high-T
c
perovskites are discussed and implications for theories of high-T
c
superconductivity are noted.
TL;DR: This work presents well-converged local-density predictions of the band structure and Fermi surface of YBa{sub 2}Cu{sub 3}O{sub 7}, giving special attention to the position of the flat Cu-O chain-derived bands and the effect of the buckling of the Cu- O chain that has been inferred by an x-ray-scattering study.
Abstract: With the appearance of angle-resolved photoemission data allowing the identification and measurement of the Fermi surface of the high-{Tc} cuprate superconductors, it is important to have precise local-density calculations with which to compare. We present well-converged local-density predictions of the band structure and Fermi surface of YBa{sub 2}Cu{sub 3}O{sub 7}, giving special attention to the position of the flat Cu-O chain-derived bands and the effect of the buckling of the Cu-O chain that is predicted by total-energy calculations and that has been inferred by an x-ray-scattering study. We emphasize the {ital c}-axis dispersion that will lead to apparent broadening of the Fermi surface in experiments interpreted in terms of a two-dimensional electronic structure.
TL;DR: In this paper, the loss peak of the AC susceptibility in polycrystalline high-T c superconductors shifts slightly to higher temperatures with increasing frequency of the applied AC magnetic field, and the magnitude of peak shift is predicted to increase with decreasing average grain size and decreasing grain boundary junction current density.
Abstract: The loss peak of the AC susceptibility in polycrystalline high- T c superconductors shifts slightly to higher temperatures with increasing frequency of the applied AC magnetic field It is shown that a flux creep term, added to the current density term in the critical state equation, can account for the observed frequency dependence The magnitude of the peak shift is predicted to increase with decreasing average grain size and decreasing grain boundary junction current density The model predictions are compared with the experimental data of Nikolo et al Some of the parameters used in the calculation are determined by fitting data for χ′ and χ″ over the full temperature range using a recently developed model for granular superconductors In addition, the relation between the intergranular pinning potential and the activation energy, which is extracted from log-frequency versus inverse χ″-peak temperature data, is clarified
TL;DR: The Ginzburg-Landau functional for a superconductor is extended to include a quantum-fluctuation term arising from imperfect screening of the long-range Coulomb interaction and it is shown that the phase stiffness is proportional to doping away from the 1/2-full Mott insulating state.
Abstract: The Ginzburg-Landau functional for a superconductor is extended to include a quantum-fluctuation term arising from imperfect screening of the long-range Coulomb interaction. At low temperatures the resulting quantum {ital x}-{ital y} model shows a second-order phase transition between a superconducting state and an insulating state as a function of the ratio of the phase stiffness to the Coulomb energy measured on the scale of the mean pair spacing. By relating the functional formulation to a BCS-type model of high-temperature superconductivity in the strongly correlated regime, we show that the phase stiffness is proportional to doping away from the 1/2-full Mott insulating state. We discuss application of the model as a mechanism for the onset of superconductivity of the CuO{sub 2}-based high-{ital T}{sub {ital c}} materials above a critical doping level. Transport and optical properties of materials with reduced transition temperature are calculated.
TL;DR: Observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of theCuO6 octahedra, and superconductivity in La2CuO4-based superconductors.
Abstract: The oxygen isotope effect on the superconducting transition temperature (α o ) varies as a function of x in La 2-x Sr x CuO 4 and La 2-x Ba x CuO 4 , with the maximum α o values (α o ≥ 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma → P4 2 /ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where α o > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of α o in both strontium- and barium-doped materials, in combination with the previously discovered Abma → P4 2 /ncm structural phase-transition in La 1.88 B 0.12 CuO 4 , suggests that an electronic contribution to the lattice instability is present and maximizes at ∼1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO 6 octahedra, and superconductivity in La 2 CuO 4 -based superconductors.
IBM1
TL;DR: On observe cette evolution pour une variete d'echantillons prepares par evaporation ou ablation laser et dont la densite de courant critique varie de trois ordres de grandeur.
Abstract: We have found that the product of the critical current and the resistance of a grain-boundary junction scale with the resistance of the boundary. This scaling is observed to hold for a variety of samples prepared by evaporation or laser ablation and whose critical current density varies by three orders of magnitude.
Abstract: The irreversibility line in high‐temperature oxide superconductors is theoretically investigated from a viewpoint of dependence on the flux‐pinning strength and a general relation between the effective pinning potential and the critical current density is derived. It is shown that the irreversibility magnetic field at 77 K in strongly pinned oxide superconductors is sufficiently high for application.
TL;DR: In this paper, the authors reported the discovery of a new class of superconductors, LixNbO2 with layered structures, which showed that at low applied magnetic fields, the magnetic susceptibility greatly decreases to diamagnetic values below 5.5 K.
Abstract: SEVERAL classes of copper oxide compounds are high-temperature superconductors1–3; the highest known transition temperature (Tc) is 122 K for Tl2Ba2Ca2Cu3O11 (ref. 4). Superconductivity has also been observed in oxides containing early transition metals, but the superconducting transition temperatures are substantially lower. (The highest known Tc for an early transition metal oxide is 13.7 K, for the spinel compound LiTi2O4 (ref. 5).) Whereas all of the copper oxide superconductors have very anisotropic structures, the superconducting oxides of early transition metals discovered up to now have three-dimensional structures. Here we report the discovery of a new class of superconductors, LixNbO2 with layered structures. At low applied magnetic fields, the magnetic susceptibility greatly decreases to diamagnetic values below 5.5 K for Li0.45NbO2 and below 5.5 K for Li0.45NbO2; this transition indicates the onset of superconductivity. In this first example of superconductivity in a layered early transition metal oxide, it is interesting to note that the layering has not increased Tc to new levels for early transition metal oxides.
TL;DR: In this article, the authors report quantitative evidence from Raman scattering for the applicability of strong-coupling theory for phonon self-energies to high-Tc superconductors.
TL;DR: In this paper, a model for high-temperature superconductors which assumes that the carriers are holes in the (hybridized) oxygen 2p band and form "spin polarons" with the moments on the copper atoms is presented.
Abstract: An outline is given of the model for some high-temperature superconductors which assumes that the carriers are holes in the (hybridized) oxygen 2p band and form ‘spin polarons’ with the moments on the copper atoms. A comparison is made with observations of spin polarons in Gd3-x v x S4 and with the properties of La1-x Sr x VO3 in relation to those of La2-x Sr x CuO4. It is assumed, following several authors, that in the superconductors the polarons form bipolarons, which are bosons, and a comparison is made with some other treatments of this hypothesis. It is proposed that in many such superconductors the boson, essentially a pair of these holes, moves in an impurity band, and that normally all the polarons (fermions) form bipolarons; the fermions repel each other on the same site (positive Hubbard U) but attract when on adjacent sites; the critical temperature T c is then that at which the Bose gas becomes non-degenerate. In such materials a non-degenerate gas of bosons would carry the current a...
TL;DR: In this paper, the authors showed that strontium lanthanum aluminate (SrLaAlO4) has considerable potential as a substrate material for high-temperature superconductor (high Tc) microwave applications.
Abstract: We have shown that strontium lanthanum aluminate (SrLaAlO4) has considerable potential as a substrate material for high‐temperature superconductor (high Tc) microwave applications. Excellent lattice match is obtainable on a 14° tilt from the c axis. The lattice dimensions encourage ab plane epitaxial growth. The thermal expansion was found to be 7.4×10−6 °C−1. Patterned sputtered niobium resonators on SrLaAlO4 exhibit Q values at 5 K comparable to similar niobium resonators on polycrystalline alumina, (Q≳10 000 from 2 to 15 GHz). Deposited YBa2Cu3O7−x (YBCO) films on this substrate show sharp ac susceptibility transitions indicating good homogeneity and ab plane orientation.
TL;DR: In this paper, the effects of temperature (4 −400 K), hydrostatic pressure and frequency on the dielectric constant, e.g., loss, and loss of single crystals of LaAlO3 and cubic yttria (9.5 mol) −stabilized zirconia (ZrO2) were investigated.
Abstract: The effects of temperature (4–400 K), hydrostatic pressure and frequency on the dielectric constant, e’, and dielectric loss of single crystals of LaAlO3 and cubic yttria(9.5 mol %)‐stabilized zirconia (ZrO2) were investigated. Both crystals are relatively low‐loss, low‐dispersion dielectrics in the temperature range (T<150 K) of most interest for high‐temperature superconductors. The pressure results make it possible to evaluate the various contributions to the temperature dependence of e’. It is found that this dependence is dominated by the change of polarizability with volume. The dielectric properties of the two crystals are compared with those of other candidate substrate materials.
TL;DR: In this paper, the phonon mean free path in polycrystalline ceramic YBa{sub 2}Cu{sub 3}O{sub 7} can be approximated using the kinetic theory approximation and reported data.
Abstract: Using the kinetic theory approximation and reported data, this study shows that at low temperatures, the phonon mean free path in polycrystalline ceramic YBa{sub 2}Cu{sub 3}O{sub 7} can be of the order of the thickness of thin-film superconductors. In this case, boundary scattering reduces the thermal conductivity with decreasing film thickness. A simple method accounts for the size effect on conduction in thin films. This analysis rests solely on geometric arguments and does not consider the effect of grain boundaries. For conduction along the film, this model approximates well an analytical solution of Boltzmann transport equation, and is in good agreement with experimental data for thin lead films. The model is also employed to analyze the size effect on conduction across the film and the influence of anisotropy.
TL;DR: This work provides a specific model for such a continuum of states in the high-{ital T}{sub {ital c}} superconductors based upon a form for the spin-fluctuation spectral weight which fits NMR data, and compares the predictions of this model with experiment.
Abstract: The linear conductance background observed in tunneling into the high-{Tc} superconductors has often been interpreted as a density-of-states effect. Here we argue that it may be due instead to strong inelastic electron tunneling from a broad, flat continuum of states. We provide a specific model for such a continuum of states in the high-{ital T}{sub {ital c}} superconductors based upon a form for the spin-fluctuation spectral weight which fits NMR data, and compare the predictions of this model with experiment.
TL;DR: A review of photoemission measurements on high-temperature superconductors is presented in this article, providing the reader with an overview of the present status of the field and future implications.
TL;DR: A scenario for high-temperature superconductivity is presented in which both phonon and electronic (charge transfer) channels are synergistically involved, and an axial oxygen-centered lattice instability accompanying the 93 K superconducting transition in YBa2Cu3O7 is presented.
Abstract: Copper K-edge x-ray absorption data indicate that an axial oxygen-centered lattice instability accompanying the 93 K superconducting transition in YBa2Cu3O7 is of a pseudo-(anti)ferroelectric type, in that it appears to involve the softening of a double potential well into a structure in which the difference between the two copper-oxygen distances and the barrier height have both decreased. This softer structure is present only at temperatures within a fluctuation region around the transition. A similar process involving the analogous axial oxygen atom also accompanies the superconducting transition in T1Ba2Ca3Cu4O11, where the superconducting transition temperature Tc is ~120 K. The mean square relative displacement of this oxygen atom in YBa2Cu3O7 is also specifically affected by a reduction in the oxygen content and by the substitution of cobalt for copper, providing further evidence for the sensitivity of the displacement to additional factors that also influence the superconductivity. On the basis of the implied coupling of this ionic motion to the superconductivity, a scenario for high-temperature superconductivity is presented in which both phonon and electronic (charge transfer) channels are synergistically involved.