Magnetic-field-induced anomalous microwave response in superconducting YBa2Cu3O7−δ thin films

• DOI: 10.1063/1.1320862
• Publication Date: 2002-07-26T13:59:53Z
• Authors: X. S. Rao; C. K. Ong; Y. P. Feng
• Keywords: Critical field

The magnetic-field-induced decrease of microwave surface impedance, Zs=Rs+jXs, superconducting YBa2Cu3O7−δ thin films is investigated using a microstrip resonator technique. Through measuring Zs as the direct current (dc) magnetic field increased from zero to certain value Hmax and subsequently decreased back zero, it found that Zs(Hdc) totally reversible if does not exceed threshold H*, at which Rs shows minimum, while irreversible larger than H*. It confirmed anomalous effect happens in vortex-free state. H* identified with lower critical for vortices penetrating into films. believed be mainly contributed by imperfect microstructure