Measurements of microwave vortex response in dc magnetic fields in Tl$_2$Ba$_2$CaCu$_2$O$_{8+x}$ films

Nicola Pompeo; Henrik Schneidewind; Enrico Silva

doi:10.1109/TASC.2019.2896531

paper

Measurements of microwave vortex response in dc magnetic fields in Tl $_{2}$ Ba $_{2}$ CaCu $_{2}$ O $_{8 + x}$ films

arXiv:1901.06541 · doi:10.1109/TASC.2019.2896531

Abstract

There is a renewed interest in superconductors for high-frequency applications, leading to a reconsideration of already known low- $T_{c}$ and high- $T_{c}$ materials. In this view, we present an experimental investigation of the millimeter-wave response in moderate magnetic fields of Tl $_{2}$ Ba $_{2}$ CaCu $_{2}$ O $_{8 + x}$ superconducting films with the aim of identifying the mechanisms of the vortex-motion-induced response. We measure the dc magnetic-field-dependent change of the surface impedance, $Δ Z_{s} (H) = Δ R_{s} (H) + i Δ X_{s} (H)$ at 48 GHz by means of the dielectric resonator method. We find that the overall response is made up of several contributions, with different weights depending on the temperature and field: a possible contribution from Josephson or Abrikosov-Josephson fluxons at low fields; a seemingly conventional vortex dynamics at higher fields; a significant pair breaking in the temperature region close to $T_{c}$ . We extract the vortex motion depinning frequency $f_{p}$ , which attains surprisingly high values. However, by exploiting the generalized model for relaxational dynamics we show that this result come from a combination of a pinning constant $k_{p}$ arising from moderate pinning, and a vortex viscosity $η$ with anomalously small values. This latter fact, implying large dissipation, is likely a result from a peculiar microscopic structure and thus poses severe limits to the application of Tl $_{2}$ Ba $_{2}$ CaCu $_{2}$ O $_{8 + x}$ in a magnetic field.

Presented at Applied Superconductivity Conference, Seattle (US) 2018. Accepted for publication on IEEE Trans. Appl. Supercond

Measurements of microwave vortex response in dc magnetic fields in Tl2​Ba2​CaCu2​O8+x​ films

Abstract

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Measurements of microwave vortex response in dc magnetic fields in Tl $_{2}$ Ba $_{2}$ CaCu $_{2}$ O $_{8 + x}$ films