Effect of Carrier Doping on Nonlinear Distortion of Signals by Superconducting Films

Faculty Mentor(s)

Dr. Stephen Remillard, Hope College

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High temperature superconductors are used in high frequency electronic devices. However, superconductor performance is limited by it’s distortion of signals under the influence of electric current. Measurements of non-linear distortion made on Tl2Ba2CaCu2O8-x (TBCCO-2212) wafers reveals dependence on carrier doping x, with grain boundaries contributing more significantly in under-doped films (x>0.1) as compared to those optimally doped (x=.1). The doping level was tuned by annealing the TBCCO-2212 thin films in a reducing nitrogen atmosphere at temperatures ranging from 250oC to 400oC. The microwave current dependent surface impedance of both pre- and post-annealed films was measured using a sapphire dielectric resonator. With the critical temperature being used as the indicator of carrier density, it was found that under-doped samples have larger nonlinear grain boundary losses as indicated by a weaker variation of surface reactance with surface resistance, revealing the preparation conditions for optimal wafer performance.


This material is based upon work supported by the National Science Foundation under NSF-RUE Grant No. PHY/DMR-1004811.

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