Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 49: Superconductivity: SQUIDs & Cryodetectors
TT 49.1: Talk
Wednesday, March 13, 2013, 17:00–17:15, H21
Dc SQUIDs with asymmetric shunt resistors — •Matthias Rudolph1, Joachim Nagel1, Johannes Maximilian Meckbach2, Matthias Kemmler1, Konstantin Ilin2, Michael Siegel2, Dieter Koelle1, and Reinhold Kleiner1 — 1Physikalisches Institut - Experimentalphysik II and Center for Collective Quantum Phenomena in LISA+,Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany — 2Institut für Mikro- und Nanoelektronische Systeme, Karlsruhe Institute of Technology, Hertzstr. 16, D-76187 Karlsruhe, Germany
We have investigated asymmetrically shunted Nb/Al-AlOx/Nb dc SQUIDs. Simulations based on the coupled Langevin equations predict that the optimum energy resolution є, and thus also the noise performance of such an asymmetric SQUID, can be 3-4 times better than that of its symmetric counterpart. While keeping the total resistance R identical to a comparable symmetric SQUID with R−1=R1−1+ R2−1, we shunted only one of the two Josephson junctions with R=R1,2/2. Both types of SQUIDs were characterized with respect to their transport and noise properties at temperature T=4.2 K, and we compared the experimental results with numerical simulations. Experiments yielded є≈ 32 ℏ for an asymmetric SQUID with an inductance L=22 pH, whereas a comparable symmetric device achieved є=110 ℏ.