Characteristics and growth of single crystals of Y1Ba2Cu3O7 with superior microwave properties

Abstract

We report the fabrication and high‐frequency characterization of single crystals of Y₁Ba₂Cu₃O₇ with extremely sharp microwave transitions. The 10 GHz surface resistance R_s is less than 400 μΩ, at temperatures 4 K below the transition temperature. The electrodynamic characteristics of these crystals were examined via several measurements, and we demonstrate that high quality crystals which show very low R_s also possess small penetration depths λ(0)=1600 Å and small magnetic field effects on the penetration depth characterized by k(0)≡(dλ/dB²)_T→0=10⁻³ Å/G². In polycrystals, and even in poor single crystals, the presence of Josephson junctions of typical effective area ∼4 μm² leads to poor microwave properties, with electrodynamic parameters orders of magnitude larger.