Nucleation of Stable Superconductivity in YBCO-Films

TL;DR

This study investigates the transition to superconductivity in YBCO films using dynamic conductivity measurements, revealing the influence of vortex loops, disorder, and defects on the superconducting transition line.

Contribution

It provides new insights into the nucleation of superconductivity, highlighting the effects of disorder and defects on the transition line in YBCO films.

Findings

Transition line $T_g(B)$ closely follows the melting line $T_m(B)$.

Disorder influences critical exponents near $T_g(B)$.

Columnar defects have limited impact on $T_g(B)$ at low fields.

Abstract

By means of the linear dynamic conductivity, inductively measured on epitaxial films between 30mHz and 30 MHz, the transition line $T_g (B)$ to generic superconductivity is studied in fields between B=0 and 19T. It follows closely the melting line $T_m (B)$ described recently in terms of a blowout of thermal vortex loops in clean materials. The critical exponents of the correlation length and time near $T_g (B)$, however, seem to be dominated by some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up to field-equivalent-doses of $B_{\phi} = 10T$ lead to a disappointing reduction of $T_g (B \to 0)$ while for $B>B_{\phi}$ the generic line of the pristine film is recovered. These novel results are also discussed in terms of a loop-driven destruction of generic superconductivity.