In our low temperature measurement laboratory we perform a variety of electrical transport experiments. This work includes exploring the properties of fractional quantum Hall states, characterizing new materials for quantum-dot-based spin qubits, and exploring hybrid semiconductor/superconductor structures to engineer topological superconducting states. Low temperature measurements are performed in a variety of cryostats, dependent on the experimental requirements.
Initial characterization is done using a variety of 4K dipper probes in helium storage dewars, with magnetic fields up to 5T. Following this initial screening, devices can be cooled to lower temperatures in large magnetic fields in one of several systems. A Janis He3 system allows samples to be cooled to T=300mK in fields up to 9T, and the system's top-loading design allows samples to be thermally cycled in as little as 3 hours. Lower temperature experiments requiring high magnetic fields can be performed at T=10mK in fields as high as 17T in the Oxford Kelvinox dilution fridge. The group also has shared access to the department's helium liquefier which enables reliable, long-term operation of these liquid helium cryostats.
The group’s ultra-low temperature capabilities were recently expanded with the addition of three cryogen-free dilution refrigerators. These include an Oxford Triton 200 with a top-loading probe and an 8T single-axis magnet, an Oxford Triton 500 with a top-loading probe and a 6-1-1 vector magnet, and a BlueFors XLD400 with a bottom loading probe and 6-1-1 vector magnet. Each of these cryogen-free systems reaches a base temperature below 10mK.
Transport experiments are conducted using a wide array of low-noise electronic equipment that enables precise measurement of mesoscopic devices to be carried out with the extremely small excitation levels required for low temperature work. Transport techniques employed in our lab include low frequency lock in measurement and RF reflectometry.