Direct correlation between Tc and CuO2 bilayer spacing in YBa2Cu3O7-x (original) (raw)
Texture, strains, and superconductivity in Y1−xPrxBa2Cu3O7−δ
Physica C: Superconductivity, 2007
We investigate the Y 1Àx Pr x Ba 2 Cu 3 O 7Àd (0 6 x 6 1) and YBa 2Ày Pr y Cu 3 O 7Àd (y = 0.1 and 0.2) polycrystalline compounds via X-ray diffraction and Raman measurements. The oxygen concentration measurements show all samples to be optimally doped or overdoped. The magnetic measurements M(T) and v ac (T) verify that the increase of the Pr content leads to the expected strong systematic decrease of the critical temperature T c and the suppression of superconductivity for x > 0.55. Systematic micro-Raman studies of the observed vibrational modes reveal a coexistence of locally different rare-earth seemingly nanoscopic environments in the mixed rare-earth Y123 systems that has been overlooked to a great extent up to now. The comparison of the Raman spectra from the two sets of compounds proves that an increased amount of Ba is occupied by Pr in Y 1Àx Pr x Ba 2 Cu 3 O 7Àd and indicates that loss of superconductivity is mainly due to hole filling by this occupancy.
Structural inhomogeneities in thin single-crystal films of YBa 2 Cu 3 O 7 − d are characterized using high resolution X-ray diffraction. Results of these measurements show a distribution in the c-axis lattice parameter and variations in the integrated intensities of (00ᐉ) diffraction peaks. Both effects can be interpreted as due to a variance in the oxygen content. Films prepared under identical growth conditions, when subjected to different post-annealing treatments showed varying structural and superconducting properties. A film with 7 − d close to 7.0 had a transition temperature (T c ) of 91 K, a width (DT c ) of 0.6 K, and a critical current density (J c ) of 6.5 × 10 6 A/cm 2 , whereas a film in which the oxygen content varied between 6.86 and 6.96 had a T c of 87 K, a DT c of 0.5 K, and a J c of 8.17 × 10 6 A/cm 2 . For each of the samples measured, the full width at half maximum (FWHM) of the (006) diffraction peak ranged between 340 and 2100 arc-seconds and was dependent on the method of preparation and the substrate. The J c s of these films were not sensitive to the quality of the film, as determined from the FWHM of the (006) peak, and the oxygen content, as determined from the (005) to (006) integrated intensity ratio. High resolution X-ray topographs showed uniform microstructure of the films, indicating that oxygen distribution is finely dispersed in the film. © 1997 Elsevier Science S.A.
Effect of strain on the structure and critical temperature in superconducting Nd-doped YBa2Cu3O7-δ
Physical Review B, 2002
A detailed study of the correlation between the superconducting critical temperature and the strain in as-grown, high-quality, c-axis epitaxial, Nd-doped YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒ films is reported. Samples with thicknesses ranging from 8 to 250 unit cells have been deposited by high-pressure oxygen sputtering on LaAlO 3 ͑100͒ single-crystal substrates. The a, b, and c axis of the films have been accurately determined by x-ray diffraction from the measurements of the ͑005͒ and the ͑038͒-͑308͒ reflections. Below a certain thickness, a crossover from orthorhombic to tetragonal structure is observed, together with a decrease of the critical temperature. These results cannot be explained by the elastic deformation of the film, but point to inelastic strain induced by the large mismatch with the substrate related to an oxygen reorganization in the Cu͑1͒-O plane.
Homogeneous superconducting gap in DyBa2Cu3O7−δ synthesized by oxide molecular beam epitaxy
Physical Review Materials
Much of what is known about high-temperature cuprate superconductors stems from studies based on two surface analytical tools, Angle-Resolved Photoemission Spectroscopy (ARPES) and Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM). A question of general interest is whether and when the surface properties probed by ARPES and SI-STM are representative of the intrinsic properties of bulk materials. We find this question is prominent in thin films of a rarelystudied cuprate, DyBa2Cu3O7-δ (DBCO). We synthesize DBCO films by oxide molecular beam epitaxy and study them by in-situ ARPES and SI-STM. Both ARPES and SI-STM show that the surface DBCO layer is different from the bulk of the film-it is heavily underdoped, while the doping level in the bulk is very close to optimal doping evidenced by bulk-sensitive mutual inductance measurements. ARPES shows the typical electronic structure of a heavily underdoped CuO2 plane and two sets of one-dimensional bands originating from the CuO chains with one of them gapped. SI-STM reveals two different energy scales in the local density of states, with one (at ~18 meV) corresponding to the superconductivity and the other one (at ~90 meV) to the pseudogap. While the pseudogap shows large variations over the length scale of a few nanometers, the superconducting gap is very homogeneous. This indicates that the pseudogap and superconductivity are of different origins.
2009
Combined synchrotron angle-dispersive powder diffraction and micro-Raman spectroscopy are used to investigate pressure-induced lattice instabilities that are accompanied by superconducting Tc anomalies in YBa2Cu4O8 and optimally doped YBa2Cu3O 7−δ , in comparison with the nonsuperconducting PrBa2Cu3O6.92. In the first two superconducting systems there is a clear anomaly and hysteresis in the evolution of the lattice parameters and increasing lattice disorder with pressure, which starts at ≈ 3.7 GPa. On the contrary, in the Pr-compound the lattice parameters follow very well the expected equation of state (EOS) up to 7 GPa. The micro-Raman data of the superconducting compounds show that the energy and width of the Ag phonons exhibit anomalies over the same pressure range where the lattice parameters deviate from the EOS and the average Cu2-O pl bond length exhibits a strong contraction that correlates with the non-linear pressure dependence of Tc. The anomalous Raman behavior is not observed for the non superconducting Pr compound, clearly indicating a connection with the charge carriers. It appears that the cuprates close to optimal doping are at the edge of lattice instability.
Correlation between superconductivity and structure in the
2011
A structural study of the incorporation of Pr-ion into the Y-site was realized in polycrystalline samples of [Y1−xPrx]Ba2Cu3O7 through of Rietveld analysis of X-ray diffraction patterns, bond valence method and electronic density diagrams correlating its doping effects on the superconducting properties. The oxygen content was checked by means of µ-Raman spectroscopy, observing the frequency position of O4-Ag phonon mode, and establishing a relationship among the O4-Ag mode frequency and the two copper sites, Cu (1) and Cu (2). Two regions are observed with Pr-rich and Y-rich microstructures. Correlación entre la superconductividad y la estructura en el sistema [Y 1−x Pr x ]Ba 2 Cu 3 O 7 Un estudio estructural de la incorporación de iones de Pr en los sítios de Y fue realizado en muestras policristalinas de [Y1−xPrx]Ba2Cu3O7 a través de: análisis de Rietveld de los patrones de difracción de rayos X, el método de enlaces de valencia y los diagramas de densidad electrónica correlaciona...
Nanomaterials, 2020
Epitaxial films of high critical temperature (T c) cuprate superconductors preserve their transport properties even when their thickness is reduced to a few nanometers. However, when approaching the single crystalline unit cell (u.c.) of thickness, T c decreases and eventually, superconductivity is lost. Strain originating from the mismatch with the substrate, electronic reconstruction at the interface and alteration of the chemical composition and of doping can be the cause of such changes. Here, we use resonant inelastic x-ray scattering at the Cu L 3 edge to study the crystal field and spin excitations of NdBa 2 Cu 3 O 7−x ultrathin films grown on SrTiO 3 , comparing 1, 2 and 80 u.c.-thick samples. We find that even at extremely low thicknesses, the strength of the in-plane superexchange interaction is mostly preserved, with just a slight decrease in the 1 u.c. with respect to the 80 u.c.-thick sample. We also observe spectroscopic signatures for a decrease of the hole-doping at low thickness, consistent with the expansion of the c-axis lattice parameter and oxygen deficiency in the chains of the first unit cell, determined by high-resolution transmission microscopy and x-ray diffraction.
Superconductivity induced by structural reorganization in the electron-doped cuprate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">mml:mrowmml:msubmml:miNdmml:mrowmml:mn2mml:mo−mml:mixmml:msubmml:miCe<...
Physical review, 2022
Electron-doped and hole-doped superconducting cuprates exhibit a symmetric phase diagram as a function of doping. This symmetry is however only approximate. Indeed, electron-doped cuprates become superconductors only after a specific annealing process: This annealing affects the oxygen content by only a tiny amount, but has a dramatic impact on the electronic properties of the sample. Here we report the occurrence of superconductivity in oxygen-deficient Nd2-xCexCuO4 thin films grown in an oxygen-free environment, after annealing in pure argon flow. As verified by x-ray diffraction, annealing induces an increase of the interlayer distance between CuO2 planes in the crystal structure. Since this distance is correlated to the concentration of oxygens in apical positions, and since oxygen content cannot substantially increase during annealing, our experiments indicate that the superconducting phase transition has to be ascribed to a migration of oxygen ions to apical positions during annealing. Moreover, as we confirm via first-principles density functional theory calculations, the changes in the structural and transport properties of the films can be theoretically described by a specific redistribution of the existing oxygen ions at apical positions with respect to CuO2 planes, which remodulates the electronic band structure and suppresses the antiferromagnetic order, allowing the emergence of hole superconductivity.
Physical Review Letters, 1999
The structure of high quality ͓YBCO N ͞PBCO M ͔ 1000 ± A superlattices, with N ranging between 1 and 12 unit cells and M 5 unit cells, grown by high oxygen pressure sputtering, is analyzed. Intracell atomic structure of the layers along the c axis and disorder at interfaces is investigated using an x-ray refinement technique. Negligible roughness, step disorder, and interdiffusion are found at the interfaces. Epitaxial mismatch strain results in a surprising reorganization of interatomic distances for the thinnest YBCO layers, which seems to correlated with the decrease in the critical temperature. Intracell structure is invoked as an additional source of T c changes in very thin YBCO layers.