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Title: Decrease of the surface resistance in superconducting niobium resonator cavities by the microwave field

Measurements of the quality factor, Q, of Nb superconducting microwave resonators often show that Q increases by ≃10%–30% with increasing radio-frequency (rf) field, H, up to ∼15–20 mT. Recent high temperature heat treatments can amplify this rf field-induced increase of Q up to ≃50%–100% and extend it to much higher fields ≃100 mT, but the mechanisms of the enhancement of Q(H) remain unclear. Here, we suggest a method to reveal these mechanisms by measuring temperature dependencies of Q at different rf field amplitudes. We show that the increase of Q(H) does not come from a field dependent quasi-particles activation energy or residual resistance, but rather results from the smearing of the density of state by the rf field.
Authors:
;  [1] ;  [2]
  1. Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)
  2. Department of Physics, and Center for Accelerator Science, Old Dominion University, Norfolk, Virginia 23529 (United States)
Publication Date:
OSTI Identifier:
22283078
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 104; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ACTIVATION ENERGY; ELECTRIC CONDUCTIVITY; HEAT TREATMENTS; MICROWAVE RADIATION; NIOBIUM; QUALITY FACTOR; QUASI PARTICLES; SUPERCONDUCTING CAVITY RESONATORS; SUPERCONDUCTORS; SURFACES; TEMPERATURE DEPENDENCE