Microwave vortex dynamics in Tl-2212 thin films

TL;DR

This study investigates vortex dynamics in Tl-2212 thin films using microwave surface impedance measurements, revealing large field-induced effects, flux line softening, and low vortex viscosity, advancing understanding of high-temperature superconductor behavior.

Contribution

The paper provides the first detailed microwave frequency analysis of vortex dynamics in Tl-2212 thin films, highlighting unique vortex parameters and flux line behavior at high frequencies.

Findings

Large field-induced variations in surface impedance.

Flux line softening with increasing magnetic field.

Vortex viscosity significantly lower than in Y-123.

Abstract

We present measurements of the effective surface impedance changes due to a static magnetic field, $\Delta Z(H,T)=\Delta R(H,T)+\rmi \Delta X(H,T)$, in a Tl-2212 thin film with $T_c>$ 103 K, grown on a CeO$_2$ buffered sapphire substrate. Measurements were performed through a dielectric resonator operating at 47.7 GHz, for temperatures 60 K$\leq T<T_c$ and magnetic fields $\leq0.8$ T. We observe exceptionally large field induced variations and pronounced super-linear field dependencies in both $\Delta R(H)$ and $\Delta X(H)$ with $\Delta X(H)>\Delta R(H)$ in almost the whole $(H,T)$ range explored. A careful analysis of the data allows for an interpretation of these results as dominated by vortex dynamics. In the intermediate-high field range we extract the main vortex parameters by resorting to standard high frequency model and by taking into proper account the creep contribution. The pinning constant shows a marked decrease with the field which can be interpreted in terms of flux lines softening associated to an incipient layer decoupling. Small vortex viscosity, by an order of magnitude lower than in Y-123 are found. Some speculations about these findings are provided.