Superconductivity Coherence in Series Array of Nb/AlOx/Nb Josephson Junctions

Paola Barbara, G. Costabile, J. Mygind +1 more

Paola Barbara, G. Costabile

Christian Schäfer

V. Lacquaniti, Domenico Andreone, Natascia De Leo +2 more

V. K. Kaplunenko, J. Mygind, N. F. Pedersen +1 more

We report on synchronous operation of series arrays of inductively coupled superconducting quantum interference devices (SQUIDs). Each array consisted of N=3 or 11 dc SQUIDs with common inductances providing a strong interaction between neighboring cells. Externally shunted (βc≊1) trilayer Nb—AlOx—Nb Josephson junctions were used. Coherent radiation was detected in the frequency range f=67–73 GHz while the array voltage was VN=NfΦ0 (Φ0=2.07×10−15 V s). The stability of the coherent state was influenced by the external dc magnetic field. The linewidth depended on the external loading. For small loading it was N times smaller than expected for a single cell. The influence of the inductive coupling mechanism on the operation of discrete Josephson junction circuits and the similarity to the coupling in layered structures of long Josephson junctions is discussed.

John B. Ketterson, Paul R. Auvil, David John Morgan +3 more

We summarize some recent activities of our group involving e-beam and optically patterned, Nb-based, superconducting nanostructures, as well as related computer modeling studies. The devices described are i) Fiske cavities buried in a Nb base layer and driven by an overlying Nb/AlOx/Nb Josephson oscillator junction, ii) Nb/AlOx/Al/AlOx/Nb five-layer double junctions which Maezava and Shoji have observed to perform as nonhysteretic SNS Josephson single junctions, and iii) critical current measurements on e-beam patterned, 2D arrays of periodic and aperiodic ferromagnetic Ni 'dots' embedded in a Nb film. We also describe a method of 'base-electrode planarization' leading to more uniform junction formation. The computer modeling studies involve the stable and unstable solution states in a static magnetic field of current-biased single and double Josephson junctions.