Pressure Tuned Quantum Phase Transitions in Model Itinerant Magnets

University Of Chicago, Chicago IL

Investigators

Abstract

Technical Abstract There has been enormous activity devoted to quantum phase transitions in complicated and often disordered materials: rare earth cuprates, heavy fermion materials, transition metal oxides and sulfides Ideally, one would like to tune a simple, stoichiometric material to its quantum critical point and directly measure the disappearance of its order parameter, thereby isolating the key physical mechanisms. Cr, the elemental antiferromagnet, offers an extraordinary opportunity to investigate the fundamental question of how magnetism emerges in metals as its spin and charge order is suppressed by pressure. Tuning the Mott-Hubbard metal-insulator transition with pressure in NiS2 similarly permits experimental access to the naked quantum singularity. Finally, direct measurements of the order parameters in CeFe2, a material sitting on the knife edge between ferro- and antiferromagnetism, should permit hard conclusions to be drawn about the possible coexistence of different magnetic ground states, with the potential for self-organization on the mesoscale. These model systems will inform the study of magnetism, quantum phase transitions, and correlated materials in general. The wide array of techniques, from x-ray scattering to magnetotransport, and the mix of physics, chemistry and materials science concepts, should train students well for careers in industry, the national laboratories, or academia. NON-TECHNICAL ABSTRACT Magnets form the basis of modern technology, from computer storage to power generation, but the important question of how magnetism originates is still largely unanswered. By squeezing the elemental magnet chromium to 100,000 atmospheres at nearly absolute zero temperature it is possible to reveal and study the very point where magnetic order first emerges from quantum disorder. Similarly, it is possible to explore the competition between different types of magnetic order, where the tendency of spins - the quantum property of an electron that makes it act like a little bar magnet inside a material - to line up parallel or antiparallel can be manipulated on length scales from nanometers to millimeters. Finally, this proposal will probe how magnetism can be coupled to the ability of materials to conduct or fail to conduct electricity. The wide array of techniques, from x-rays to electrical conduction, and the necessity to combine concepts from physics, chemistry and materials science, should train students well for careers in industry, the national laboratories, or academia. Bringing research perspectives to education is another emphasis, both for the P.I. and the graduate students in the laboratory. This includes public lectures, course development for both science and non-science majors, mentoring for K-8 students in the local schools, and outreach activities as part of a citywide program.