Sub-Picosecond Stress-Induced Conductivity Transitions, Mechanical Transitions and Ferroelectric Transitions

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Nontechnical Description: This project investigates material behavior under a fast stress pulse. When a solid object is hit by a very fast force under ambient temperature, one could simulate the condition under absolute zero temperature, which is the coldest state any substance can attain. This is because, with the force lasting less than one period of atomic vibration, atoms in the solid stay so still that they behave as if they were at the coldest state! To probe this possibility, this project utilizes a recent invention of the team to generate an ultrafast long-range force from an ultrafast electron bunch, and then study the response of materials hit by such force, at ambient temperature. The results observed may hold the key to some fundamental materials science questions as well as certain technological ones, such as how fast an electronic device can turn on-and-off. An education plan is also integrated into the research to provide laboratory and distal learning, community outreach and new graduate textbooks.Technical Description: This project investigates stress-induced transitions of conductivity, mechanical properties and ferroelectricity of solid materials at the sub-picosecond, sub-atomic-vibration limit when atomic migration is frozen and dislocation and domain wall movement is less than one atomic spacing. It provides the perfect setting for revealing (a) the real-time action of electron-phonon interaction, which can cause electron de-trapping, and (b) coherent crystal rotation/shear, which can cause twinning plasticity and nanodomain ferroelasticity. The experiments utilize a recent invention of the team: the relativistic magnetic field of a 20 GeV electron/positron bunch can induce, in a metal-insulator-metal structure, a 0.1 ps transient current that generates a 0.1 ps self-force. Much faster than the prior record of ~1 ns stressing, sub-ps stressing challenges our fundamental understanding of mechanical behavior at the atomic level, probes the fundamental limit of ferroic switching, and manifests electron-phonon interactions in condensed matter in real time. As such interactions are often involved in charge trapping and de-trapping, these experiments can establish the fundamental speed limit for charge-trapping devices.