A ruthenium oxide thermometer for dilution refrigerators operating down to 5 mK

•Parasitic rf heating saturates RuO2 thermometer readings at low temperatures.•A new thermometer using best rf filtering practices maintains sensitivity to 5 mK.•Heating via black body radiation likely originates within the cryogenic space.•Filtering within the experimental space required to reach t...

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Bibliographic Details
Published in:Cryogenics (Guildford) 2021-10, Vol.119, p.103367, Article 103367
Main Authors: Myers, Sean A., Li, Hongxi, Csáthy, Gábor A.
Format: Article
Language:English
Subjects:
Attenuation
Balancing
Black body radiation
Circuits
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Dilution
Frequency filters
Heating
OTHER INSTRUMENTATION
Refrigerators
Resistance thermometers
Rf filtering
Ruthenium oxide
Sensitivity
Temperature sensors
Thermalization
Thermometers
Thermometry
tThermalization
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Summary:•Parasitic rf heating saturates RuO2 thermometer readings at low temperatures.•A new thermometer using best rf filtering practices maintains sensitivity to 5 mK.•Heating via black body radiation likely originates within the cryogenic space.•Filtering within the experimental space required to reach the lowest temperatures. At the lowest temperatures achieved in dilution refrigerators, ruthenium oxide resistance thermometers often saturate and therefore lose their sensitivity. In an effort to extend the range of such temperature sensors, we built a thermometer which maintains sensitivity to 5 mK. A key component of this thermometer is an in situ radio frequency filter which is based on a modern rf absorption material. We show that the use of such a filter is only effective when it is encased in the same rf-tight enclosure as the ruthenium oxide sensor. Our design delivers an attenuation level that is necessary to mitigate the effects of parasitic heating of a fraction of pW present in our circuit. Furthermore, we show that the likely origin of this parasitic heating is the black body radiation present within the experimental space of the refrigerator. We found that the equilibration time of the thermometer increases rapidly as the temperature is lowered; below 5 mK this thermometer becomes impractical because of the prohibitively long equilibration times.
ISSN:0011-2275
1879-2235
DOI:10.1016/j.cryogenics.2021.103367