Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 7: Superconductivity: Cryodetectors

TT 7.10: Talk

Monday, March 31, 2014, 12:15–12:30, HSZ 03

Magnetic Johnson noise thermometry for µ K temperatures — Daniel Rothfuss, •Andreas Reiser, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut für Physik, Universität Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg

Noise thermometry instrinsically is a non-driven method. When minimal heat input is required this method is highly advantageous. Our noise thermometer is a magnetic Johnson noise thermometer. The noise source is a cold-worked high purity copper cylinder with a diameter of 5 mm and a length of 20 mm. The magnetic flux fluctuations caused by the brownian motion of the electrons are measured inductively by two dc-SQUID magnetometers simultaneously. The signals from these two channels are cross-correlated. This leads to a reduction of parasitic noise by more than one order of magnitude. Applying this technique together with the highly sensitive SQUID preamplifiers allows the measurement of the tiny noise powers at microkelvin temperatures. Experimentally we characterized the thermometer for temperatures between 43   µ K and 0.8   K. The measuring time is approximately 400 seconds for one temperature, the extremely low heat input to the thermometer allows a continuous measurements without heating effects.