Negative Thermal Expansion Near Structural Quantum Phase Transitions

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Non-technical abstract: The effect of thermal expansion can be seen throughout the physical world in varied contexts, from sidewalk cracks to icebergs. While all materials exhibit this basic property, the vast majority of materials expand when heated. However, recent new material discoveries have revealed cases of negative thermal expansion (NTE), a peculiar phenomenon of heat-induced volume contraction. This team recently observed that strong NTE occurs in some materials when more than one atomic lattice structure is stable at very low temperatures. This circumstance is an example of a quantum phase transition, where anomalous material behavior is often observed in different contexts. This work is of general interest in the pursuit of exploiting quantum properties of matter to advance technology and impact society. Research pursued uses multiple experimental techniques including X-ray scattering and optical spectroscopy to measure magnetic and electronic responses under various conditions around structural Quantum Phase Transitions which exhibit NTE. The research heavily involves undergraduate researchers who pursue independent projects related to science and education while gaining exposure to research in both university and national lab settings. New curricular reform efforts in introductory physics courses will involve elementary quantum concepts taught at the level of wave mechanics while rollout of a massive new educational reform initiative commences.Technical abstract: The research activities of this award designed to explore the basic science of NTE materials and address the apparent connection between NTE and structural quantum phase transitions. This award supports a broad effort to explore this connection and unusual physical effects in select NTE materials. Primary experimental techniques include laser-based optical experiments to generate and measure sound pulses, high resolution inelastic X-ray scattering, and magnetic susceptibility on single crystals and powder samples of select NTE materials, incorporating low-temperature strain control in some experiments. Additional aspects of the project include creating opportunities for undergraduate student participation in university- and national laboratory-based experimental condensed matter research with additional options in physics education research related to a redesign of calculus-based introductory physics courses. Metrics for a massive implementation of a new studio-style physics teaching initiative are analyzed to inform and direct best practices. In addition, hands-on demonstration tools related to NTE are developed for students and by students.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.