Probing the electric field-induced doping mechanism in YBa2Cu3O7 using computed Cu K-edge x-ray absorption spectra (original) (raw)
Related papers
Electric field-induced oxygen vacancies in YBa2Cu3O7
The Journal of Chemical Physics
The microscopic doping mechanism behind the superconductor-to-insulator transition of a thin film of YBa2Cu3O7 was recently identified as due to the migration of O atoms from the CuO chains of the film. Here, we employ density-functional theory calculations to study the evolution of the electronic structure of a slab of YBa2Cu3O7 in the presence of oxygen vacancies under the influence of an external electric field. We find that, under massive electric fields, isolated O atoms are pulled out of the surface consisting of CuO chains. As vacancies accumulate at the surface, a configuration with vacancies located in the chains inside the slab becomes energetically preferred, thus providing a driving force for O migration toward the surface. Regardless of the defect configuration studied, the electric field is always fully screened near the surface, thus negligibly affecting diffusion barriers across the film.
The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa2Cu3O6+x (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbitals during the MST of optimally doped YBCO leads to substantial hole-transfer from the chains into the planes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transfer configurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXS spectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting state and, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. In the quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) in perovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens a unique novel channel for studying the dynamics of HTSC.
In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X
Proceedings of the National Academy of Sciences of the United States of America, 2017
Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-ins...
Band structure of YBa2Cu3Ox in relation with the oxygen vacancy distribution
Solid State Communications, 1987
The electronic band structure and the density of states of the YBa2Cu30 x superconductor are computed for x.= 7 using the extended Hiickel scheme. Two ordered arrangements of the oxygen vacancies in the basal Cu-O planes have been considered. It is shown that the oxygen vacancy distribution plays a major role in the electronic structure of this compound and deeply influences the density of states at the Fermi level.
Physical Review Letters, 2007
We use microprobe Angle-Resolved Photoemission Spectroscopy (µARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two dimensional (2D) electronic structure with nearly momentum independent bilayer splitting is observed. The splitting energy is 150 meV at (π,0), almost 50% larger than in Bi2Sr2CaCu2O 8+δ and the electron scattering at the Fermi level in the bonding band is about 1.5 times stronger than in the antibonding band. The CuO chains have a quasi one dimensional (1D) electronic structure. We observe two 1D bands separated by ∼ 550meV: a conducting band and an insulating band with an energy gap of ∼240meV. We find that the conduction electrons are well confined within the planes and chains with a non-trivial hybridization. PACS numbers: 74.25.Jb, 74.72.Hs, 79.60.Bm
Physical Review B, 1990
A detailed analysis of the effect that oxygen disorder has on the electronic structure ol the highly correlated high-T, superconductors is presented. The system is modeled by a Hubbard-type Hamiltonian in which the on-site and intersite correlations between oxygen and copper atoms are included. The Green-function formalism is used to calculate the local electronic density of states at the Cu and 0 sites characteristic of YBa2Cu306+, as a function of oxygen concentration x and of the cation charge Q. Due to the large electronic interactions, a Mott-Anderson metal-nonmetal transition is obtained, in accordance with the experimental findings. The hole concentration n is calculated for disordered and ordered systems. A plateau in the concentration dependence of n is obtained for 0.45&x~0.75, only in the ordered system. The correlation functions of the various charge states in Cu and 0 are also calculated and discussed.
Chemical activity in YBa2Cu3O7−δ across the normal to superconducting phase transition
Microchemical Journal, 2011
The Gibbs free enthalpy, chemical activity across the transition temperature to superconductivity, T c in YBa 2 Cu 3 O 7-δ is obtained from reciprocally enhanced X-Ray absorbance, XAS and diffraction, XRD data near the Ba L 3,2 edges' energy E a , and orientations in the X-ray beam for preferred Miller indexed [HKL] planes' scattering that are enhanced near T c. The standard enthalpy and entropy for the formation of mixed normal metal/superconducting domains above T c , determined individually across the two Ba L 3,2 edges, to better than a percent accuracy: ∆H ≠ > =-220 meV, and ∆S ≠ > =-2 meV/K when 121>T>92K≈T c1 , indicate there is energy available to form the mixture and the reduced entropy indicates there is also order increase. Below T c the standard enthalpy and entropy to form at least two mixed superconducting phases is halved to ∆H ≠ < =-86 meV, ∆S ≠ < =-1 meV/K when 92K>T>T c2 ≈72K. Thus reciprocal XAS/XRD enhancement at orientations in the X-ray field, of preferred 2D planes, induced by the transition to superconductivity in the layer solid, indicates one, the importance of the 2D-plane electron density scattering near T c , and two, identifies the 2D-plane chemical activity, by the electron density leading to symmetry allowed excitations, a role similar to that of the electron density in linear bonds for molecular activity.
Physica C: Superconductivity, 2005
We report systematic studies of structural, microstructural and transport properties of Y 1-x Ca x Ba 2 Cu 3 O 7-δ bulk samples with 0.20 ≥ x ≥ 0.0. The partial substitution of Ca 2+ at Y 3+ site in YBa 2 Cu 3 O 7-δ leads towards slightly overdoped regime, which along with disorder in CuO 2 planes is responsible for decrease in superconducting transition temperature (T c ) of the doped system. The microstructural variants being studied by transmission electron microscopy (TEM) technique in imaging and selected area diffraction modes revealed an increase in the density of twins with increase in Ca concentration despite the fact that there is slight decrease in the orthorhombicity. This is against the general conviction of decrease in twin density with decreasing orthorhombicity. An increase in twin density results in sharpening of twin boundaries with increasing Ca concentration. These sharpened twin boundaries may work as effective pinning centers. A possible correlation between microstructural features and superconducting properties has been put forward and discussed in the present investigation.
Chemical Activity in YBa2Cu3O7-delta Acrosst the Transition to Superconductivity
2011
Changes in the Gibbs free enthalpy, chemical activity across the transition temperature to superconductivity Tc in YBa2Cu3O7-delta is described by enhanced element X-Ray absorption XAS and diffraction XRD [HKL] reflections. Critical oscillations in the index of refraction within the XAS line width (± 2.5eV) at the Ba L2, L3 and Y K-edges observed ˜30K above Tc 93K in [HKL] reflections indicates their activity. Enhanced absorbance A versus T obtains the activation enthalpy and entropy: deltaH^>=-220 meV, deltaS^>=-2 meV/K (121>T>93K) for mixed normal and superconducting phases, which compensates the reported O atom ordering activation energy near Tc by 50 meV. The activation needed to mix differently ordered superconducting phases: deltaH^<= -67 meV, deltaS^< = -1 meV/K (60K<T<93K) indicates lattice ordering persists to 60K. Enhanced XRD scattering induced near the transition to superconductivity in 3D solids indicates that the role of 2D reactive [HKL] planes...