Dissipative Phenomena in High Temperature Superconducting Ybco Thin Film Microstrips
Abstract
Dissipation in Type-II superconductors is caused by the motion of magnetic flux lines (vortices). I have measured the linear and nonlinear current-voltage characteristics of thin film microstrips of the high temperature superconductor rm YBa_2Cu_3O_{7 -delta} for temperatures in the range 30 K to 100 K and magnetic fields from 0 to 8 Tesla. I argue that in zero applied field, two dimensional vortex -antivortex pairs induced above a Kosterlitz-Thouless transition account for the linear resistivity, and that three dimensional vortex-ring nucleation and expansion induced by large current densities accounts for the nonlinear resistivity. I also argue that in nonzero magnetic fields, a somewhat analogous transition occurs between a vortex liquid phase at high fields and temperatures, and a vortex glass phase at low fields and temperatures, for which dissipation is observable only at large current densities. In the vortex glass-like phase, I analyze the exponent mu that characterizes the nonlinearity of resistivity on current density, and find that mu varies smoothly with temperature and magnetic field, unlike the plateau values observed in experiments by Dekker on thicker films. In the vortex liquid phase, I find that the longitudinal resistivity rho_{xx} shows activated and diffusive regimes at low and high temperatures, respectively. The transverse (Hall) linear resistivity is negative for a range below T_{c } and scales as rho_sp {xx}{1.5}, as found in previous investigations. I find that the nonlinear rho _{xy} shows similar behavior as nonlinear rho_{xx}.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT........61C
- Keywords:
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- YTTRIUM BARIUM COPPER OXIDE;
- Physics: Condensed Matter; Engineering: Materials Science