Superconducting and ferromagnetic properties of NbN/NiCu and NbTiN/NiCu bilayer nanostructures for photon detection
- Author(s)
- A. Klimov, R. Puzniak, B. Aichner, W. Lang, E. Joon, R. Stern, W. Slysz, M. Guziewicz, M. Juchniewicz, M. A. Borysiewicz, R. Kruszka, M. Wegrzecki, A. Laszcz, A. Czerwinski, Roman Sobolewski
- Abstract
Performance of superconducting single-photon detectors based on resistive hotspot formation in nanostripes upon optical photon absorption depends strongly on the critical current density JC of the fabricated nanostructure. Utilization of an ultrathin, weak-ferromagnet cap layer on the top of a superconducting film enhances of the structure€™s JC due to an extra flux pinning. We have fabricated a number of both NbN/NiCu and NbTiN/NiCu superconductor/ferromagnet (S/F) ultrathin bilayers and microbridges. NbN and NbTiN underlayers with thicknesses varying from 4 to 7 nm were grown using dc-magnetron sputtering on chemically cleaned sapphire single-crystal substrates. After rapid thermal annealing at high temperatures, the S films were coated with Ni0.54Cu0.46 overlayers with thicknesses of about 6 nm, using cosputtering. Compositions of the deposited films were confirmed by EDX spectroscopy analysis, while TEM studies demonstrated excellent epitaxial quality of our S layers with ∼2-nm-thick F/S transition layer and atomically-sharp S/substrate interface. Magnetic properties of bilayers were studied using both the SQUID and Vibrating Sample Magnetometer techniques in low and high magnetic fields. Low-temperature tests confirmed that in all cases NiCu films were ferromagnetic with the Curie temperature of above 30 K. Below the bilayer critical temperature of approx. 12-13 K, the structures were fully proximitized with the strong superconducting signal. For superconducting transport properties characterization, we used bilayers patterned into 40-1/4m-long microbridges with the width varying from 0.4 1/4m to 2 1/4m. The same S/F nanostructures were also used to study their superconducting fluctuations. The temperature dependence of magnetoresistance demonstrated highly 2-dimensional character with an unusual negative region that extended almost to room temperature. In the S/F sample, the fluctuations were observed to be substantially below theoretical expectations.
- Organisation(s)
- Electronic Properties of Materials
- External organisation(s)
- Polish Academy of Sciences (PAS), National Institute of Chemical Physics & Biophysics (NICPB), Institute of Electron Technology
- No. of pages
- 10
- DOI
- https://doi.org/10.1117/12.2179697
- Publication date
- 2015
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103026 Quantum optics, 103021 Optics, 103033 Superconductivity, 103009 Solid state physics
- Keywords
- ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Applied Mathematics, Electrical and Electronic Engineering, Computer Science Applications
- Portal url
- https://ucris.univie.ac.at/portal/en/publications/superconducting-and-ferromagnetic-properties-of-nbnnicu-and-nbtinnicu-bilayer-nanostructures-for-photon-detection(24ee38af-2782-4383-9add-75d03c9d42c7).html