Hiroyuki Enomoto

XPS measurements in Bi2Sr2Ca1−xYxCu2O8+d

We performed X-ray photoemission spectroscopy (XPS) measurements in Bi 2 Sr 2 Ca 1−x Y x Cu 2 O 8+d system in order to investigate the relation between the Cu valence and superconductivity. The negative chemical shift of the Cu 2p spectra indicated that holes in the Cu site decreased with increasing Y concentration. The change in the shape and the positive chemical shift of the O 1s spectra indicated that holes on the oxygen site in Cu-O layer increased with increasing Y concentration. The superconducting transition temperature decreased monotonically with decreasing the Cu valence and vanished when the Cu valence became less than 2.

X-ray photoemission spectroscopy study on Bi2Sr2-x Ca1+x Cu2O8+d

Abstract We have elucidated the distribution of the Sr and Ca atoms in the Bi2Sr2-x Ca1+x Cu2O8+d system (0  ′  0.8) by X-ray photoemission spectroscopy (XPS). The carrier concentration and the superconducting temperature Tc have a maximum at x = 0.2 and then monotonously decrease with increasing x. From the XPS measurements, the Sr3d and Ca2p spectra are found to be decomposed into two states. We have clarified the occupation of the Sr and Ca atoms in the Sr-and Ca-layers and found that the deficiency in the Sr-layer has a great influence on superconductivity.

Observation of Rotating Angle Dependence of Tunneling Spectra in Heavily Doped n-Type Silicon

We observed the rotating angle dependence of tunneling spectra in n-type Si, which behavior reflects the anisotropic nature of the Fermi surface of Si. This behavior confirms the conservation of the transverse component of the electron wave vector in tunneling.

Preparation of Bi-Sr-Ca-Cu-O superconducting films by the liquid phase epitaxial method

Bi-Sr-Ca-Cu-O superconducting films were prepared on MgO(100) single-crystal substrates by the liquid phase epitaxial (LPE) method using Bi 2 Sr 2 CaCu 2 O x solution. X-ray diffraction measurements and scanning electron microscopy analyses revealed that films were predominantly oriented with the c -axis perpendicular to the substrate surfaces. The as-grown film consisted of the 10 K and 80 K phases. After the post-annealing, films mainly consisted of the 80 K phase.

Y doping effect on superconducting properties in Bi2Sr2CaCu2O y films prepared by liquid phase epitaxial method

Abstract The Y doping effect on superconducting properties has been studied in Bi2Sr2CaCu2O y films prepared by the liquid phase epitaxial method. The incorporation ratio of each element in the LPE film to that in the melt was investigated as a function of Y content in the solution. The change of the superconducting properties due to the Y doping was connected with the total amount and the composition ratio of Sr, Ca and Y in the film.

Effect of Ba substitution for Sr in Bi2Sr2CaCu2O y superconducting films prepared by rf-sputtering method

Abstract In order to investigate the effect of the distance between the CuO2 layer and the SrO layer, d Cu-Sr, on the superconductivity in the Bi2Sr2CaCu2O y system, we have substituted Ba for Sr. Bi-(Sr, Ba)-Ca-Cu-O superconducting thin films were prepared by the rf-magnetron sputtering method. Rietveld analysis was employed to estimate d Cu-Sr. Samples with various d Cu-Sr were obtained by changing the post-annealing temperature as well as the Ba concentration. Tc was found to increase with increasing d Cu-Sr.

Effect of Pb substitution for Ca in Bi2Sr2CaCu2O y

Abstract Guided by the fact that Pb4+ has an ionic radius very close to Ca2+, Pb substitution for Ca in Bi2Sr2CaCu2O y has been made via solid state reaction using Bi2O3, SrCO3, CaCO3, CuO and PbO2 as precursor materials. Single-phase samples have been prepared in the range of Pb concentrations between zero and twenty percent. The X-ray diffraction peaks were indexed on an orthorhombic unit cell whose dimensions change only along the c direction, increasing slightly with the Pb concentration. The onset of the superconducting transition was observed to increase with increase in Pb content. The synthesized materials are positive carrier superconductors. The carrier concentration decreases with increasing Pb content. The effect of Pb on the surrounding atoms is discussed from the point of view of core level XPS on the samples.

XPS study of the electronic states of Cu-O layer in Bi-Sr-Ca-Cu-O superconductors

Abstract A Cu2p core electron XPS study is carried out for Bi2Sr2Ca1-x M x Cu2O y (M = Y, Nd). A model for the electronic structures which explains the XPS results is presented. The model reproduces the O2p characters of the upper part of the valence band when the holes are present.