Applied Superconductivity - Walther Meißner Institut - Bayerische ...

158 R. GROSS AND A. MARX Chapter 4the first observation of macroscopic quantum interference in superconductivity. 4,5 However, later in thelate 1960s and early 1970s the rf-SQUID was preferred, mainly since it was easier to fabricate singlejunction interferometers using a simple point-contact. However, then in 1975 J. Clarke and co-workersshowed that the energy sensitivity of dc-SQUIDs can be improved by using externally shunted junctionsto values better than those of the rf-SQUID. 6 This made the use of dc-SQUIDs preferable in applicationsrequiring optimum resolution. Despite the improvement of rf-SQUIDs, their energy sensitivity is stillworse than that of dc-SQUID at 4 K. However, at 77 K both types of SQUIDs are comparable makingrf-SQUIDs again attractive for SQUIDs based on the high temperature superconductors.4 J. Clarke, Phil. Mag. 13, 115 (1966).5 R.L. Forgacs, A. Warnick, Rev. Sci. Instr. 18, 214 (1967).6 J. Clarke, W.M. Goubau, M.B. Ketchen, Appl. Phys. Lett. 27, 155 (1976); J. Low Temp. Phys. 25, 99 (1976).© Walther-Meißner-Institut