Acquisition of a Dilution Refrigerator

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Electronic interactions in metals can produce a rich variety of interesting phenomena including superconductivity, magnetic order, heavy fermion behavior, non-Fermi liquid behavior, Kondo effect, and valence fluctuations, many of which are not well understood. Valuable information needed for developing an understanding of the microscopic interactions that produce these phenomena can be obtained from measurements of the properties of materials that exhibit these phenomena at low temperatures. This award provides support for a dilution refrigerator (DR) which will be used for measurements of low temperature properties of strongly correlated electron systems. The DR system will provide a base temperature of less than 10 milliKelvins with a cooling power of 250 microwatts at 100 milliKelvins, and a large amount of experimental access. Several accessories will be added to the basic system, including resistance thermometry for measuring the temperature of the sample mounted below the mixing chamber, and a 9 tesla superconducting magnet system for measurement in high magnetic fields. Studies in the milliKelvin range are especially important for some materials with very low energy scales including heavy fermion superconductors, low ordering temperature magnets, heavy fermion and Kondo compounds, and those exhibiting time-dependent phenomena associated with quantum tunneling. Very often, investigations to ever lower temperatures yield unexpected behavior, revealing new lower energy scales associated with the many-body ground state. These studies are of fundamental scientific interest and are also of importance in the development of useful materials for industrial applications.