Abstract
We present measurements of the electron temperature using gate defined quantum dots formed in a GaAs 2D electron gas in both direct transport and charge sensing mode. Decent agreement with the refrigerator temperature was observed over a broad range of temperatures down to 10 mK. Upon cooling nuclear demagnetization stages integrated into the sample wires below 1 mK, the device electron temperature saturates, remaining close to 10 mK. The extreme sensitivity of the thermometer to its environment as well as electronic noise complicates temperature measurements but could potentially provide further insight into the device characteristics. We discuss thermal coupling mechanisms, address possible reasons for the temperature saturation and delineate the prospects of further reducing the device electron temperature.
Highlights
Two-dimensional electron gases (2DEGs) are a versatile, widely-used experimental platform in low temperature solid state physics because of their nearly ideal two-D
In the direct transport measurements, we might suspect lifetime broadening of the quantum dot level as a limiting factor
The temperatures obtained with the charge sensor are not lower than the temperatures measured in direct transport, despite much lower dot tunneling rates
Summary
Two-dimensional electron gases (2DEGs) are a versatile, widely-used experimental platform in low temperature solid state physics because of their nearly ideal two-. A wide range of phenomena contain small energy scales and are only accessible at very low temperatures These include novel nuclear spin quantum phases in 2D [8,9] and in interacting 1D conductors [10,11] and multiple impurity [12] or multiple channel [13,14] Kondo physics. The lowest reliable temperature reported in a 2DEG is 4 mK [17,18] in a fractional quantum Hall experiment, with sintered silver heat exchangers attached to the sample wires in a 3He cell. We have proposed a way to overcome these limitations by integrating a copper nuclear refrigerator into each of the electrical sample wires connected to an electronic transport sample, providing efficient thermal contact to a bath at low mK or microkelvin temperature [36]. In semiconductor samples such as GaAs 2DEGs, the ohmic contacts will probably present the largest electrical and thermal impedance in this cooling scheme
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