Microwave properties of borocarbide superconductors RNi₂B₂C (R=Y,Er,Tm,Ho)

Abstract

We report measurements of the microwave surface impedance of the borocarbide family of superconductors RNi₂B₂C (R=Y,Er,Tm,Ho). The experiments enable direct measurements of the superfluid density, and are particularly sensitive to the influence of magnetic pair breaking. In HoNi₂B₂C the antiferromagnetic transition is clearly observed at zero field, and leads to a drastic reduction of the superfluid density, which recovers at lower temperatures. In ErNi₂B₂C the antiferromagnetic transition is not seen in zero-field data. Magnetic effects are responsible for anomalies in the low-temperature surface impedance below approximately 4 K in HoNi₂B₂C and TmNi₂B₂C. The temperature dependence of the microwave impedance disagrees with BCS calculations.