Pair-breaking description of the vortex-depinning critical field in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ thin films

The penetration length λ of c-axis-oriented thin films of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ in perpendicular magnetic fields H up to 14 T is determined from complex impedance measurements at 1.25 kHz. Vortex core pinning determines the functional form of λ(T,H). The observed nonlinear temperature dependence of the depinning critical field, identified by λ→∞, can be described within the context of a pair-breaking formalism in which a type-II clean-limit pair-breaking rate (∝$H^{1/2}$) replaces the dirty-limit rate (∝H).