Fabrication and characterization of micropillar Josephson junction with Niobium Nitride and Permalloy/Samarium Cobalt exchange spring magnet*

Adam Bowen, Jiyeong Gu  

Department of Physics and Astronomy, California State University, Long Beach, Long Beach, CA 90840 

Superconductors are prevalent in cutting-edge technology and research, such as MRI, quantum computers, and particle accelerators. The superconducting proximity effect occurs when the superconductor is adjacent to non-superconducting material since the superconducting condensate, pairs of electrons known as Cooper pairs, leaks into a non-superconducting material. We fabricated micropillar Josephson junctions in hybrid superconductors and attempted to observe the odd triplet effect of superconductor (S)/ferromagnet (F)/superconductor (S/F/S) system. First Nb was used for S and a ferromagnetic exchange spring system of Permalloy (Py) and Samarium Cobalt (SmCo) were used for F. Due to the low superconducting critical temperature (Tc) of Nb we had a difficulty measuring the Josephson current in S/F/S junction. Therefore, in this work we introduce new superconductor NbN which has much higher bulk Tc. We found Tc increased a lot from ~3.3 K for 100 nm Nb thin film to ~9.3 K for 100 nm NbN thin film. To optimize Tc of NbN thin film, N2 gas was introduced during the magnetron sputtering process. NbN thin films at different ratio of N2/Ar gas were made and Tc dependence on the ratio was investigated.