Nathan Newman
Arizona State University, USA
Title: In-situ electron paramagnetic resonance studies of performance-degrading defects in superconducting microwave resonators
Biography
Biography: Nathan Newman
Abstract
We have determined the physical nature and concentration of performance-degrading point defects in the dielectrics of superconducting planar microwave resonators using in-situ electron paramagnetic resonance (EPR) spectroscopy. This has been accomplished by measuring parallel plate and stripline resonator quality-factors as a function of the magnitude of a magnetic-field applied parallel to the electrode surfaces. YBa2Cu3O7-δ (YBCO) thin film electrodes proved to be a preferred choice over Nb and MgB2 because they are readily available and have a small surface resistance (Rs) up to high temperatures (~77 K) and magnetic fields (i.e. < 1 Tesla). Measurements of stripline resonators with Mn2+ and Co2+-doped Ba(Zn1/3Ta2/3)O3 and Ba(Zn1/3Nb2/3)O3 dielectrics are found to have losses dominated by spin-excitations (i.e. EPR absorption) in the dielectric, even without an applied magnetic field. Measurements of parallel-plate-resonators using very-pure sputtered Si dielectric layers on an unheated substrate are found to have a ~7 x 1018 cm-3 concentration of paramagnetic defects with properties similar to that reported in amorphous Si. Annealing is found to annihilate the paramagnetic defects to below measureable quantities.
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