Title of Dissertation: TUNNELING AND RAMAN SPECTROSCOPIES OF THE ELECTRON-DOPED HIGH-TEMPERATURE SUPERCONDUCTORS Muhammad Mumtaz Qazilbash, Doctor of Philosophy, 2004 Dissertation directed by: Professor Richard L. Greene Department of Physics This thesis consists of spectroscopic studies of the electron-doped high temperature cuprate superconductors Pr2−xCexCuO4−δ (PCCO) and Nd2−xCexCuO4−δ (NCC...

Polycrystalline samples of Ca(1-x)Gd(x)MnO(3-δ) (x = 0.00, 0.02, and 0.05) have been studied by X-ray diffraction (XRD), electrical resistivity (ρ), thermoelectric power (S), and thermal conductivity (κ). All the samples were single phase with an orthorhombic structure. The Seebeck coefficient of all the samples was negative, indicating that the predominant carriers are electrons over the entir...

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The incommensurate spin fluctuation of the doped triangular antiferromagnet is studied within the t-J model. It is shown that the commensurate peak near the half-filling is split into six incommensurate peaks in the underdoped and optimally doped regimes. The incommensurability increases with the hole concentration at lower dopings, and saturates at higher dopings. Although the incommensurabili...

(Bi,Sr)FeO3-δ (BSF) cathode materials doped with either Co, Ni or Mn are synthesized by an ethylene diamine tetra-acetic acid (EDTA)-citrate complexing method, and the effects of the doping level on the mixed electronic-ionic conductivity at various temperatures are studied up to 800 °C. The phase purity and solid solution limit are investigated by X-ray diffraction (XRD). The ionic conductivit...

Some recent experiments that provide support for the concept of topological doping in cuprate superconductors are discussed. Consistent with the idea of charge segregation, it is argued that the scattering associated with the “resonance” peak found in YBa2Cu3O6+x and Bi2Sr2CaCu2O8+δ comes from the Cu spins and not from the doped holes.

We report on the ab-plane optical reflectance measurements of single crystals of Y-doped Bi2Sr2CaCu2O8+δ and Pr-doped YBa2Cu3O7−δ over a wide frequency range from 80 to 40 000 cm−1 (10 meV–5 eV) and at temperatures between 20 and 300 K. Y and Pr doping both decrease the hole concentration in the CuO2 planes. This has allowed us to investigate the evolution of ab-plane charge dynamics at doping ...

The studies of the bipolar resistive switching effect in thin film heterojunctions (YBa2Cu3O7-δ /Ag) and (Nd 2-x Ce x CuO4-y /Ag) have exhibited the role of oxygen as a doping element in hole- and electron-doped HTSC compounds.

A recent analysis of optical conductivity data which has provided evidence for coupling of the charge carriers to the 41meV spin resonance seen in the superconducting state of optimally doped YBa2Cu3O6.95 (Y123), is extended to other systems. We find that the corresponding spin resonance is considerably broader in Tl2Sr2CuO8+δ (Tl2201) and YBa2Cu4O8 (Y124) than it is in Bi2Sr2CaCu2O8+δ (Bi2212)...