title: Low-noise nano superconducting quantum interference device operating in Tesla magnetic fields.
abstract: Superconductivity in the cuprate YBa(2)Cu(3)O(7) (YBCO) persists up to huge magnetic fields (B) up to several tens of Teslas, and sensitive direct current (dc) superconducting quantum interference devices (SQUIDs) can be realized in epitaxially grown YBCO films by using grain boundary Josephson junctions (GBJs). Here we present the realization of high-quality YBCO nanoSQUIDs, patterned by focused ion beam milling. We demonstrate low-noise performance of such a SQUID up to B = 1 T applied parallel to the plane of the SQUID loop at the temperature T = 4.2 K. The GBJs are shunted by a thin Au layer to provide nonhysteretic current voltage characteristics, and the SQUID incorporates a 90 nm wide constriction which is used for on-chip modulation of the magnetic flux through the SQUID loop. The white flux noise of the device increases only slightly from 1.3 μΦ(0)/(Hz)(1/2) at B = 0 to 2.3 μΦ(0)/(Hz))(1/2) at 1 T. Assuming that a point-like magnetic particle with magnetization in the plane of the SQUID loop is placed directly on top of the constriction and taking into account the geometry of the SQUID, we calculate a spin sensitivity S(μ)(1/2) = 62 μ(B)/(Hz))(1/2) at B = 0 and 110 μ(B)/(Hz))(1/2) at 1 T. The demonstration of low noise of such a SQUID in Tesla fields is a decisive step toward utilizing the full potential of ultrasensitive nanoSQUIDs for direct measurements of magnetic hysteresis curves of magnetic nanoparticles and molecular magnets.
authors.affiliation: Physikalisches Institut-Experimentalphysik II and Center for Collective Quantum Phenomena in LISA+, Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Schwarz
authors.forename: Joachim
authors.initials: J
authors.lastname: Nagel
authors.forename: Roman
authors.initials: R
authors.lastname: Wölbing
authors.forename: Matthias
authors.initials: M
authors.lastname: Kemmler
authors.forename: Reinhold
authors.initials: R
authors.lastname: Kleiner
authors.forename: Dieter
authors.initials: D
authors.lastname: Koelle
mesh_terms: D003198:Computer Simulation; D004553:Electric Conductivity; D060526:Magnetic Fields; D008962:Models, Theoretical; D011789:Quantum Theory