Impedance-matched coplanar-waveguide metal-powder low-pass filters for cryogenic applications.

We developed impedance-matched metal-powder low-pass filters based on coplanar waveguide design and characterized them at room temperature and 77.4 K. The coplanar waveguide metal-powder (CPW-MP) filters have a return loss better than 9.8 dB at frequencies up to 10 GHz at 77.4 K. We find that the filter attenuation per length scales linearly with frequency from 29 to 220 dB/m within the 1-5 GHz frequency range at 77.4 K, achieving the total attenuation above 100 dB for the 1 m-long CPW-MP filter at frequencies above 2 GHz. The CPW-MP filter integrated with the multipole LC filter demonstrates the low cut-off frequency, the attenuation above 100 dB in the stop band, and the high roll-off of 590 dB per decade. The proposed CPW-MP filter is easy to fabricate, has very good thermal-shock resistance, is flexible for integration with other types of low-pass filters, delivers the same performance as classical cryogenic filters, is more compact compared to 50 Ω coax cables with the same type of lossy dielectric, and provides ample opportunities for further miniaturization.

In-Plane Anisotropy of Electrical Transport in Y0.85Tb0.15Ba2Cu3O7-x Films.

We fabricated high-quality c-axis-oriented epitaxial YBa2Cu3O7-x films with 15% of the yttrium atoms replaced by terbium (YTBCO) and studied their electrical properties. The Tb substitution reduced the charge carrier density, resulting in increased resistivity and decreased critical current density compared to pure YBa2Cu3O7-x films. The electrical properties of the YTBCO films showed an in-plane anisotropy in both the superconducting and normal states that, together with the XRD data, provided evidence for, at least, a partially twin-free film. Unexpectedly, the resistive transition of the bridges also demonstrated the in-plane anisotropy that could be explained within the framework of Tinkham's model of resistive transition and the Berezinskii-Kosterlitz-Thouless (BKT) model, depending on the sample parameters. Measurements of the differential resistance in the temperature range of the resistive transition confirmed the occurrence of the BKT transition in the YTBCO bridges. Therefore, we consider the YTBCO films to be a promising platform for both the fabrication of devices with high kinetic inductance and fundamental research on the BKT transition in cuprate superconductors.