Holes In CuO2 Planes Research Articles

The relationship between orbital hybridization and superconductivity of sm-doped YBa2Cu3O7–δ studied by x-ray spectroscopy

Sm-doped YBa2Cu3O7–δ samples were prepared by conventional solid state reaction method in air. The studies of X-ray photoemission spectroscopy and X-ray absorption spectroscopy indicate that the extra electrons fill the holes in CuO2 planes, so that the hole carrier concentration decrease under Sm substitution. The X-ray absorption spectroscopy of Cu L-edge and O K-edge demonstrates that the hybridization strength between Cu 3d and O 2p decreases with increasing content of Sm, but the hybridization strength between Y 4d, Ba 5d, Sm 4f and O 2p increases with the increasing of Sm content, while the superconductivity of the Sm-doped YBa2Cu3O7–δ samples is suppressed, i.e., the superconducting transition temperature of the samples was lowered. Thus, our experimental results suggest a close relationship between the superconductivity and orbital hybridization.

Local structure and superconductivity in (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x compounds

In this work, a close correlation between variations of critical temperature (Tc) and the hole concentration of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x systems was studied. The (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x samples were fabricated using the solid-state reaction method, where x ranged from 0 to 0.2. The Tc values of the samples deduced from magnetization versus temperature measurement gradually decreased with increasing the Fe3O4 content (x). To investigate a possible reason for the observed decrease in the values of Tc in the samples, the valence state of copper (V) and the hole concentration (p) in all samples were examined by analyzing the Cu K-edge and Cu L2,3-edge X-ray absorption near edge structure (XANES) spectra. The values of V and p monotonously decreased with the increase in Fe3O4 doping content (x) and agreed with the behavior of Tc. The existence of Fe3+ was confirmed by analyzing Fe L2,3-edge XANES. Hence, Fe3+ ions possibly entered the lattice structure of the samples and filled the holes in CuO2 planes. The degradation of superconductivity in Fe3O4 doped samples was then explained.

A Simple Model for Investigation of the Pair Breaking Effect on the Parameters of HTS/FM Thin Films

A simple model was proposed for description of Cooper pair breaking effect (which is caused by transfer of spin-polarized carriers from the ferromagnetic (FM) manganite into the high temperature superconductor (HTS)) on the critical temperature and the microwave surface impedance of HTS/FM heterostructures. The model is based on the assumption on an exponential dependence of the Cooper pairs concentration (as well as number of the holes in CuO2 planes, responsible for the superconductivity) on the distance from HTS/FM interface. The model fits well the thickness dependence of HTS film parameters and is used for evaluation of the penetration depth of spin-polarized particles into HTS in the HTS/FM structures.

Structural phase transitions and superconductivity in La-M-Cu-O compounds

Abstract The structural phase transitions D17 4h→D18 2h→D164h in La2-x M x CuO4 compounds and their influence on electronic spectrum for oxygen doped holes in CuO2 plane are considered on the basis of a micro-scopical anharmonic model. The free energy and equation for the two-component order parameter are calculated in the self-consistent phonon approximation. Taking into account the electron-phonon interaction with the soft tilting mode and other phonon branches the dependence of the superconducting temperature Tc on hole concentration n is obtained. A dip in Tc(n) dependence is found at the transition to the low temperature tetragonal phase (LTT) owing to splitting of two oxygen bands at half-filling.

BOND VALENCE CHARACTER AND SUPERCONDUCTIVITY IN Y1-xPrxBa2Cu3O7-δ SYSTEM

Based on data of neutron diffraction measurements, the oxidation states in Y1-xPrxBa2Cu3O7-δ system are determined by bond valence sums (BVS) calculation. It is found that a close correlation between the BVS value of Cu(2) and superconducting critical temperature (Tc) exists. We believe that the increase of Pr content leads to the variation of charge distribution when the content of oxygen remains almost constant. At the same time ,the BVS value of Cu(l) and Cu(2) decreases,while that of Y(Pr) increases,and the holes in CuO2 plane are partly localized in Pr-O bond. The quenching of superconductivity by Pr ions is mainly attributed to this localization of the holes in CuO2 plane by Pr ions.

Inelastic neutron scattering study of YBa2Cu3O6+x

Inelastic neutron scattering measurements on YBa2Cu3O6+x single crystals are reported. In the antiferromagnetic phase (x= 0.15, TN= 410K) the two-dimensional character of the spin wave spectrum and the value of the exchange parameters have been established. A small amount of holes in CuO2 planes (x ⋍ 0.37, nh ⋍ 1.8 %, TN = 180 K) strongly modifies the low energy spectrum : the spin wave velocity is reduced and in-plane excitations are overdamped.