Cooling electrons in nanoelectronic devices by on-chip demagnetisation

Jones, Alexander and Pashkin, Yuri and Prance, Jonathan (2019) Cooling electrons in nanoelectronic devices by on-chip demagnetisation. PhD thesis, Lancaster University.

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Abstract

This thesis describes a novel cooling technique which allows the electrons within nanoelectronic devices to reach new low temperatures: nuclear demagnetisation of copper refrigerant mounted directly onto the chip a device is constructed on. This is within a field which has expanded in interest in recent years, due to the promise of new low electron temperatures allowing the investigation of new physical phenomena, the better fidelity of fundamental quantum effects and the improvement in quantum technologies such as quantum computers and sensors. Throughout the study, the effectiveness of the new technique is verified by applying it to a CBT, a nanoelectronic device which provides primary (accurate without any need for calibration) thermometry of its own internal electron temperature. This thesis follows the development of this technique, starting from the initial proof of concept measurements made using a commercial, cryogen free, dilution refrigerator, as would be found in many low temperature and quantum transport laboratories. Here, the device electrons were cooled from 7 mK, the base temperature of the dilution refrigerator, to 4.5 mK without using any other elaborate experimental constructions, opening the technique up to many other laboratories. This technique was then furthered by applying it to a newly adapted CBT which has the lowest operation temperature capability yet reported of 300 μK. This was done in a dilution refrigerator custom built in Lancaster, resulting in a minimum electron temperature of 1.20 ± 0.03 mK. This has opened the door to a new temperature regime in which to study new quantum effects, and going forward this technique will therefore be applied to other devices in order to enable these further investigations.