Acquisition of Instrumentation for Cooling Semiconductor-based Low-Dimensional Electron Systems to T~1mK in a Large Magnetic Field

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This grant provides funding to acquire instrumentation at the California Institute of Technology for research on low-dimensional correlated electron systems in semiconductors. The instrumentation will allow the investigation of these systems at low temperatures down to 1milliKelvin, a factor of ten below current practice. In addition, the instrumentation will allow large magnetic fields, up to 16 Tesla, to be applied to the samples at low temperatures. The need to work at, or near the temperature of 1milliKelvin is related to the steady improvement in the quality and complexity of the semiconductor heterostructure samples that are available. This trend has led to numerous encounters with subtle electron correlation phenomena whose thorough study demands lower temperatures than are available using conventional helium dilution refrigeration. Prominent among the phenomena requiring study near 1milliKelvin are the so called even-denominator fractional quantized Hall effects; the recently discovered, yet unpredicted, insulating phases of the 2 dimensional electron gas in the first excited Landau level; and the remarkable properties of bilayer electron gases in the strongly coupled limit. The latter is particularly interesting since it is beginning to appear as if this system is an example of a long-predicted, yet elusive, collective state known as an excitonic superfluid. There is the possibility of new discoveries when the technical limitation of the dilution refrigeration is lifted by the new instrumentation.This instrumentation acquisition will have impact the education of graduate and undergraduate students at Caltech. Graduate students, in pursuit of their Ph.D. degrees, will be able to perform experiments that are at the cutting edge of research on low-dimensional correlated electron systems. Students will become experienced with the very advanced experimental techniques needed to work in the low temperature/high magnetic field regime. This technical experience will help them successfully compete for jobs in the academic, national lab, and industrial environments. Undergraduate students, through both summer time research and research participation courses during the academic year, will also be able to work with this new instrumentation. The prospect of establishing a state-of-the-art apparatus for pursuing correlated electron physics into the 1milliKelvin temperature regime has already caught the imagination of the students in the group. Underrepresented minority and female researchers (both graduate and undergraduate students) have participated in the NSF-funded resarch and their participation will continue. This new instrumentation will provide important opportunities for these students.