Microwave surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7- delta /

Abstract

The magnetic-field dependence of the microwave surface resistance of both single crystals and sintered crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) has been measured at 24 GHz. The resistance decreases below the superconducting transition temperature and reaches a constant residual resistance. The value is much lower for single crystals than for polycrystals. Furthermore, polycrystals showed magnetoresistance at low field and magnetoresistance with hysteresis at high field, which resembles the magnetization behavior of typical type-II superconductors. The observed magnetoresistance is shown to be inherent to a sintered polycrystal which is composed of grains and contains many voids. The single crystal showed lower magnetoresistance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>