Temperature dependence of electrodynamic properties of YBa2Cu3Oy crystals

Abstract

The temperature dependences of the radio-frequency penetration depth ${\lambda }_{\mathrm{ab}}$, microwave surface resistance $R_s$, and the lower critical field $H_{c1}$ were measured for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{y}}$ crystals. Pair-breaking effects of magnetic fields on ${\lambda }_{\mathrm{ab}}$, represented by a parameter k==d${\lambda }_{\mathrm{ab}}$/d($H^2$), were also measured. The temperature dependences of all these parameters ${\lambda }_{\mathrm{ab}}$, $H_{c1}$, k, and $R_s$ are in good agreement with the Bardeen-Cooper-Schrieffer temperature dependences for an s-wave superconductor, and suggest a mean-field behavior of the gap parameter.