Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 30: Superconductivity - Applications II : Levitation, SQUID-based Sensors, Devices

TT 30.4: Vortrag

Dienstag, 8. März 2005, 17:30–17:45, TU H104

Novel, non-contact noise thermometer for milli-Kelvin temperatures — •Astrid Netsch, Elena Hassinger, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut für Physik, Universität Heidelberg, Im Neuenheimer Feld 227, D-69120 Heidelberg

The temperature dependence of thermal voltage noise of an electrical resistance is described by the dissipation-fluctuation theorem, which directly reflects our basic understanding of statistical physics and thermodynamics. This made the measurement of noise an attractive option for primary thermometry in a wide range of temperatures. A lot of investigations have been made on that topic but parasitic heat input and the suitable fabrication of the resistor still causes frequently problems.

We present a novel technique for Johnson-noise thermometry which uses a commercial dc-SQUID as preamplifier. The noise to be measured is generated by the thermal motion of electrons in a bulk sample of high purity gold, which cause fluctuations of magnetic flux in a pickup coil being connected to the input coil the SQUID-magnetometer. The thermometer is easy to fabricate, shows a linear dependence of spectral power density upon temperature below 4 K and is rather insensitive to typical sources of parasitic heating. We discuss general design considerations of such thermometers as well as the dependence of temperature uncertainty upon measurement time and show a comparison of our prototype to the present international temperature scale PLTS-2000 provided by a superconducting reference device (SRD1000) which contains ten fixed-points between 15.4 mK and 1175.8 mK.