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TT: Fachverband Tiefe Temperaturen
TT 9: SC: Poster Session
TT 9.44: Poster
Montag, 22. März 2010, 14:00–18:00, Poster A
Dc SQUIDs with sub-micron-sized Nb/HfTi/Nb Josephson junctions for operation in high magnetic fields — •Joachim Nagel1, Oliver Kieler2, Konstantin Konovalenko1, Johannes Kohlmann2, Alexander Zorin2, Reinhold Kleiner1, and Dieter Koelle1 — 1Physikalisches Institut – Experimentalphysik II and Center for Collective Quantum Phenomena and their Applications, Universität Tübingen, Auf der Morgenstelle 14, D-72076, Germany — 2Fachbereich 2.4 "Quantenelektronik", Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany
We investigate the suitability of dc superconducting quantum interference devices (SQUIDs) for operation in high magnetic fields (up to B≈ 100 mT) at temperature T = 4.2 K. The micro SQUIDs with superconductor (S) - normal metal (N) - superconductor (S) sub-micrometer Josephson junctions were realized using Nb electrodes and HfTi for the normal interlayer. Our fabrication technology combines e-beam lithography and chemical-mechanical polishing which enables junction sizes down to 200 nm× 200 nm, integrated into small superconductor rings with inner dimensions down to 0.5 µ m× 0.5 µ m. The characteristic voltage of the SNS junctions is typically 30 − 40 µV with a McCumber parameter βC < 0.1, and a screening parameter of the SQUIDs βL≈ 0.2. The SQUIDs where characterized by measurements of electric transport and noise (using a Nb dc SQUID amplifier) in a magnetically shielded environment as well as in high magnetic fields. The SQUIDs show very low flux noise which is a major prerequisite for their application as detectors for magnetic properties of nanoparticles.