טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMuntaser Naamneh
SubjectCritical Current in Bi2Sr2CaCu2o8+ Thin Films
DepartmentDepartment of Physics
Supervisor Professor Kanigel Amit
Full Thesis textFull thesis text - English Version


Abstract

Since the discovery of high temperature superconductors, maximizing the critical current density, Jc, was one of the most important goals of applied superconductivity research. Tremendous efforts have been made to enhance Jc by improving the pining forces, but these attempts are ultimately limited by de-pairing and de-pining effects. De-pairing occurs when enough kinetic energy is supplied to the system to break up the superconducting pairs (thus the material reverts to normal state). De-pining, on the other hand, is governed by the interplay between flux motion and flux pining, and marks the onset of power dissipation in a sample still in the superconductive state. Due to this dissipation, superconductivity is lost before the de-pairing current is reached.

Large critical currents can be achieved by improving the pining force and its distribution. Some studies have shown that oxygen doping in Bi2Sr2CaCu2O can create pinning centers, and play a role in determining the critical current. It is therefore of physical and technical interest to investigate the effect of oxygen doping on Jc.

In the present study, high quality c-axis oriented Bi2Sr2CaCu2O thin films were prepared using a DC sputtering system, then patterned into a narrow bridge. We change the doping of the bridge by repeating an annealing process at various temperatures and oxygen pressures. For each doping level, we perform I-V measurements at various temperatures. It was found that the behavior of I-V characteristic at high voltages is consistent with the theory of Larkin-Ovchinnikov (LO). From each I-V measurement, we obtain the critical current. We find that the dependence of the critical current on temperature is the same for all doping levels, and is consistent with the Ginzburg-Landu (GL) theory. It was also found that the zero temperature critical current exhibits a peak at a unique doping level at the slightly overdoped regime.