Superconducting order parameter fluctuations in NbN/NiCu and NbTiN/NiCu bilayer nanostripes for photon detection

Author(s)
Bernd Aichner, Florian Jausner, Georg Zechner, Rita Mühlgassner, Wolfgang Lang, Andrii Klimov, R. Puzniak, W. Slysz, M. Guziewicz, R. Kruszka, M. Wegrzecki, Roman Sobolewski
Abstract

Thermodynamic fluctuations of the superconducting order parameter in NbN/NiCu and NbTiN/NiCu superconductor/ferromagnet (S/F) thin bilayers patterned to microbridges are investigated. Plain NbN and NbTiN films served as reference materials for the analyses. The samples were grown using dc-magnetron sputtering on chemically cleaned sapphire single-crystal substrates. After rapid thermal annealing at high temperatures, the superconducting films were coated with NiCu overlays, using co-sputtering. The positive magnetoresistance of the superconducting single layers is very small in the normal state but with a sharp upturn close to the superconducting transition, a familiar signature of superconducting fluctuations. The fluctuation-enhanced conductivity (paraconductivity) of the NbN and NbTiN single layer films is slightly larger than the prediction of the parameter-free Aslamazov-Larkin theory for order-parameter fluctuations in two-dimensional superconductors. The addition of a ferromagnetic top layer, however, changes the magnetotransport properties significantly. The S/F bilayers show a negative magnetoresistance up to almost room temperature, while the signature of fluctuations is similar to that in the plain films, demonstrating the relevance of both ferromagnetic and superconducting effects in the S/F bilayers. The paraconductivity is reduced below theoretical predictions, in particular in the NbTiN/NiCu bilayers. Such suppression of the fluctuation amplitude in S/F bilayers could be favorable to reduce dark counts in superconducting photon detectors and lead the way to enhance their performance.

Organisation(s)
Electronic Properties of Materials
No. of pages
8
DOI
https://doi.org/10.1117/12.2270877
Publication date
05-2017
Publication status
Published
Peer reviewed
Yes
Austrian Fields of Science 2012
103033 Superconductivity, 210005 Nanophotonics, 103018 Materials physics, 103009 Solid state physics
Portal url
https://ucris.univie.ac.at/portal/en/publications/superconducting-order-parameter-fluctuations-in-nbnnicu-and-nbtinnicu-bilayer-nanostripes-for-photon-detection(de3b4a39-bdaa-47fe-a9a6-7574cbd0c360).html