Measurement of small supercurrents in niobium SQUID circuits

• Published in: Physica. C, Superconductivity Vol. 352; no. 1; pp. 141 - 143
• Main Authors: Il'ichev, E., Hoenig, H.E., Meyer, H.-G., Zorin, A.B., Khanin, V.V., Götz, M., Pavolotsky, A.B., Niemeyer, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2001
• Subjects: Josephson energy; Radio-frequency method; SQUID; Supercurrent; 74.50+r; Radio-frequency method; SQUID; 85.25 Cp; Josephson energy; Supercurrent
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(00)01710-X

Applying a radio-frequency (rf) interference method, we were able to investigate the supercurrent across Josephson junctions down to some tens of nA, where the Josephson coupling energy is considerably smaller than the thermal energy at 4.2 K, the temperature of operation. We report about the measurement of small supercurrents by a rf interference method. The critical current I c as well as the supercurrent-phase relation were derived from the measurement of the impedance of the phase-biased Josephson element at 10–30 MHz. Several single and double Nb/AlO x /Nb tunnel junctions with critical currents ranging from 50 nA to 3 μA have been studied. As expected, highly asymmetrical double junction structures exhibited a harmonic current-phase relation, while the latter indeed distinctly deviated from sin ϕ in the case of more balanced double junctions.