Effect of phase fluctuations on superconducting states with anisotropic order parameters is studied in a BCS like lattice model of cuprate superconductors. The degradation of the mean field transition temperature due to phase fluctuations is estimated within a Kosterlitz-Thouless scenario. Values of the interaction parameters for optimal doping, corresponding to a stable superconducting state o...

We synthesized powder samples of NaxCoO2 · yH2O changing the volume of the water in the hydration process, then investigated their superconducting properties,. It was proved that the volume of water is one of key parameters to obtain a single phase of NaxCoO2 · yH2O with good superconducting properties. The transition temperature, Tc, of the sample changed gradually while it was stored in the a...

The theoretical description of the thermodynamic properties of ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale is proposed. Their superconducting characteristics strongly depend on the mutual orientation of the ferromagnetic layers. In addition, depending on the transparency of S/F interfaces, the superconducting critical temperature can exhibit four different typ...

We report on a scanning superconducting quantum interference device microscope operating at temperatures down to 20 mK in a dilution refrigerator. The instrument is designed for studying quantum mechanical coherence effects in mesoscopic systems and investigating magnetic effects on a mesoscopic length scale in novel materials. We have demonstrated the low-temperature operating capabilities of ...

We compare magnetotransport of the three iron-arsenide-based compounds ReFeAsO Re=La, Sm, Nd in very high DC and pulsed magnetic fields up to 45 and 54 T, respectively. Each sample studied exhibits a superconducting transition temperature near the maximum reported to date for that particular compound. While high magnetic fields do not suppress the superconducting state appreciably, the resistiv...

We use angle resolved photoemission spectroscopy to study the momentum dependence of the superconducting gap in NdFeAsO0.9F0.1 single crystals. We find that the Gamma hole pocket is fully gapped below the superconducting transition temperature. The value of the superconducting gap is 15+/-1.5 meV and its anisotropy around the hole pocket is smaller than 20% of this value-consistent with an isot...

We have performed measurements of the surface impedance in the normal and superconducting states of the title compounds in the millimeter wave-frequency range (1-3 cm-1), and have evaluated the complex conductivity for different crystallographic orientations. Above the transition temperature, the materials behave like metals with a scattering rate of approximately 20 cm -1. In the superconducti...

– A phenomenological theory is suggested to explain the experimentally discovered “paramagnetic peculiarity” and the unconventional change of the energetic state of a layers of high Tc of Y-Ba-Cu-O in the vicinity of the phase transition. The physical conditions are found under which these peculiarities are revealed. It is shown that the suggested theory qualitatively describes the experimental...

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...