EAGER: CRYO: Development of materials and techniques to enable sub-Kelvin cooling via adiabatic decompression of para-nematic materials.

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Part 1: Non-Technical SummaryResearchers at Stanford University develop a new method to cool materials to within a degree of absolute zero without requiring the use of costly liquid helium. Such extreme temperatures are necessary for a variety of modern technologies, including some realizations of quantum computers. This high risk/high reward project, which is jointly supported by the Division of Chemical, Bioengineering, Environmental and Transport Systems and the Division of Materials Research, investigates an approach that works by alternately squeezing materials and then releasing the strain. While the operating principle is straight forward, the technique requires discovery of appropriate materials with very specific physical properties. The proposed research will identify and characterize such materials to enable a more sustainable approach to ultra-low temperature cooling. Part 2: Technical SummaryResearchers at Stanford University investigate a new approach to reaching sub-Kelvin temperatures. The method works by alternately squeezing materials and then releasing the strain, through the process of adiabatic decompression referred to in the award title. For the functional material, a specific class of rare earth containing compounds are considered, for which large temperature changes are possible for modest changes in induced strain, i.e. para-nematic materials. The researchers’ approach to use such materials for cryogenic cooling has several specific advantages over existing technologies: it does not require He-3, it does not require magnetic fields, and it can be rapidly cycled. The project, which is jointly supported by the Division of Chemical, Bioengineering, Environmental and Transport Systems and the Division of Materials Research, has three main objectives: development of appropriate candidate materials; improvement in low-T characterization of their thermo-elastic properties; and reduction to a working thermodynamic cycle. Activities to be performed include crystal growth and characterization of candidate materials; measurement of low-temperature elastocaloric response over a wide range of strains; improvements in thermometry; and design, construction and testing of a simple working model that would demonstrate such a cooling effect.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.