Low vibration and low temperature closed-cycle cryostat for oxide MBE and laser-ARPES

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This proposal is for the purchase of a closed-cycle recirculating chiller to upgrade the low temperature cryostat of the Quantum Materials and Devices Foundry (QMDF) led by George Sawatzky at UBC. The goal of the facility is to study the properties of materials comprised of layers of different compounds known as heterostructures, and phenomena arising at the interfaces between these layers. In particular, QMDF aims at engineering transition-metal oxide and dichalcogenide heterostructures, growing them by molecular beam epitaxy (MBE), and to comprehensively characterizing them in situ as they are being fabricated layer-by-layer. While QMDF will be used to explore a large number of phenomena, the immediate goal is to study unconventional superconductivity in thin film iron pnictides and nickelates, as they might be the key materials to answer the most intriguing question in modern condensed matter: what is the nature of unconventional superconductivity and how to create a room temperature superconductor. *******The cryostat to be upgraded is used for mapping of electronic bands in heterostructures by means of angle resolved photoemission spectroscopy (ARPES), the main characterization method associated with the facility. Unlocking the mystery of high-temperature superconductivity might be hiding in subtle details of the electronic band structure, and it is imperative to gain information with high signal to noise ratio and high energy and momentum resolution. In turn, this requires the samples under investigation to be held at cryogenic temperatures for an extended time while under study. The challenge is to find a cost-effective method of keeping the sample stable to better than 0.1K at all cryogenic temperatures down to 3K.*******Low temperature experiments today can be undertaken using two methods: (1) the direct use of liquid helium (flow cryostat, currently used); or (2) the use of a closed cycle refrigeration system. While the latter allows us to reach lower temperatures using pumped helium, it cannot run constantly for more then a few days, is prone to sample temperature and position drift, and is exorbitantly expensive to run. On the one hand, a typical ARPES facility equipped with a flow cryostat costs about $100,000/year consuming one of the earth's most precious and non-renewable resources, releasing much of it back into the atmosphere. On the other hand, a typical closed cycle cryostat is not able to operate below about 10K. Our goal, is to combine the technological advances in cryogenic design that will allow UBC's flow cryostat to reach very low temperatures with a cryogen free refrigeration system produced by Janis Research Company.*******This upgrade will provide the Quantum Materials and Devices Foundry with dramatically increased experimental running times, which are essential for accurately measuring the electronic properties of some of the new exotic samples that are now being routinely grown at UBC.