Pressure Tuned Quantum Phase Transitions in Model Itinerant Magnets

技术摘要在复杂且常常是无序的材料中，有大量的活动致力于量子相变：稀土铜氧化物，重费米子材料，过渡金属氧化物和硫化物理想地，人们希望将简单的化学计量材料调谐到其量子临界点，并直接测量其序参数的消失，从而隔离关键的物理机制。元素反铁磁体Cr提供了一个非凡的机会来研究磁性如何在金属中出现的基本问题，因为它的自旋和电荷顺序受到压力的抑制。用NiS 2中的压力调节Mott-Hubbard金属-绝缘体转变同样允许实验接近裸量子奇点。最后，直接测量CeFe 2（一种位于铁磁性和反铁磁性之间的刀刃上的材料）的序参数，应该可以得出关于不同磁性基态可能共存的硬结论，并具有在介观尺度上自组织的潜力。这些模型系统将为磁性、量子相变和相关材料的研究提供信息。广泛的技术，从x射线散射到磁输运，以及物理，化学和材料科学概念的混合，应该培养学生在工业，国家实验室或学术界的职业生涯。非技术摘要磁铁构成了从计算机存储到发电的现代技术的基础，但磁性如何起源的重要问题在很大程度上仍然没有答案。通过在接近绝对零度的温度下将元素磁体铬压缩到100，000个大气压，有可能揭示和研究磁有序首次从量子无序中出现的点。类似地，我们也可以探索不同类型的磁序之间的竞争，其中自旋的趋势--电子的量子特性，使其在材料中表现得像一个小条形磁铁--平行或反平行排列的趋势可以在从纳米到毫米的长度尺度上操纵。 最后，这项提案将探讨磁性如何与材料导电或不导电的能力相结合。广泛的技术，从X射线到导电，以及从物理，化学和材料科学的联合收割机概念的必要性，应该培养学生在工业，国家实验室或学术界的职业生涯。将研究视角引入教育是另一个重点，无论是对P.I.和实验室里的研究生。这包括公开讲座，科学和非科学专业的课程开发，为当地学校的K-8学生提供指导，以及作为全市计划一部分的推广活动。

Technical AbstractThere 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 ABSTRACTMagnets 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.