Fig. 2: Experimental platform for cooling low-dimensional electrons.
From: Cooling low-dimensional electron systems into the microkelvin regime
a Schematic diagram of the metal immersion cell. Silver sinter on the silver base thermalises the liquid 3He to the nuclear demagnetisation refrigerator. The copper lid holds the 2DEG device, the sinter heat exchangers for cooling the I± and V± lines, the 2DEG noise thermometer (NT), and a red light-emitting diode (LED) for illuminating the 2DEG. The NT and its heater were connected using wedge-bonded resistive Au wires and superconducting Al wires acting as thermal breaks62. Another NT is mounted on the nuclear stage (NS) to measure the 3He bath temperature Tbath. The base and the lid sealed with In comprise a He-tight and photon-tight enclosure, complete with a Ag sinter plug in the filling capillary. All incoming electrical connections are fitted with low-pass filters of three types: b discrete RC filters with R = 1 kΩ and C = 10 nF, c insulating Cu powder filters63, and, d Ag epoxy filters with 1 m-long NbTi wires embedded in conducting Ag epoxy. RF-tight coaxial connections were used between these filters and the walls of the immersion cell. Ag epoxy filters with multiple wires, compatible with SQUID NT readout, were used on the SQUID lines. e The inside of the copper lid of the cell, with the Au and Al wires highlighted and the LED shown schematically. The NT is housed in a Nb shield, shown here with the top removed.
