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Full-Text Articles in Physical Sciences and Mathematics

Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel Sep 2003

Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel

Chemistry Faculty Publications and Presentations

The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above …


High Pressure Effects On Electron Transport And Structure Of Colossal Magnetoresistive Materials, Congwu Cui May 2003

High Pressure Effects On Electron Transport And Structure Of Colossal Magnetoresistive Materials, Congwu Cui

Dissertations

Pressure effects on the electronic, magnetic properties and structure of several typical colossal magnetoresistive manganites, La0.60Y0.07Ca0.33MnO3, Pr1-xCaxMn03 (X = 0.25, 0.30, 0.35), Nd1-xSrxMnO3 (x = 0.45, 0.50), were explored through high pressure resistivity and structure measurements. It was shown that pressure up to ~7 GPa induces more complicated charge, spin and lattice state changes than in the low pressure range explored previously. In La0.60Y0.07Ca0.33MnO3, pressure induces a local atomic structure transformation at a critical …


Monte Carlo Analysis Of Gan-Based Gunn Oscillators For Microwave Power Generation, R. P. Joshi, V. Sridhara, P. Shah, R. D. Del Rosario Jan 2003

Monte Carlo Analysis Of Gan-Based Gunn Oscillators For Microwave Power Generation, R. P. Joshi, V. Sridhara, P. Shah, R. D. Del Rosario

Electrical & Computer Engineering Faculty Publications

Monte Carlo studies of transferred electron oscillators based on bulk wurtzite GaN are presented. Two structures have been examined: (i) devices with the conventional single notch structure, and (ii) repetitive structures with serial segments to fashion a "multiple domain" device. Wurtzite material has been chosen because of the higher drift velocity and because analytical expressions for the band structure have recently become available. Performance parameters of interest such as the operating frequency, output power, and conversion efficiency are calculated. Variations due to changes in temperature, biasing voltage, and device length are also included. It is shown that multidomain Gunn diodes …