Pressure Tuned Quantum Phase Transitions in Model Itinerant Magnets

技术摘要在复杂和通常无序的材料：稀土铜酸盐、重费米子材料、过渡金属氧化物和硫化物中，已经有了巨大的活动致力于量子相变。理想的情况下，人们希望将一个简单的化学计量材料调整到它的量子临界点，并直接测量它的序参数的消失，从而隔离关键的物理机制。元素反铁磁体CR提供了一个非同寻常的机会来研究金属中的磁性是如何出现的这个基本问题，因为它的自旋和电荷顺序被压力抑制。在NiS2中用压力调节Mott-Hubbard金属-绝缘体转变类似地允许实验访问裸露的量子奇点。最后，直接测量CeFe2中的有序参数，应该可以得出关于不同磁性基态可能共存的结论，并有可能在介观尺度上自组织。CeFe2是一种位于铁磁性和反铁磁性之间的尖端材料。这些模型系统将为磁学、量子相变和相关材料的研究提供一般信息。从X射线散射到磁传输的各种技术，以及物理、化学和材料科学概念的结合，应该会很好地培养学生在工业、国家实验室或学术界的职业生涯。从计算机存储到发电，磁体构成了现代技术的基础，但磁性如何起源这个重要问题在很大程度上仍未得到解答。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，就有可能揭示和研究量子无序中最早出现磁序的那个点。同样，可以探索不同类型的磁序之间的竞争，在这种情况下，自旋的倾向可以在从纳米到毫米的长度尺度上进行操纵。自旋是电子的量子特性，使其在材料内部像小条形磁铁一样排列。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关联。从x射线到电导的各种技术，以及将物理、化学和材料科学的概念结合在一起的必要性，应该会很好地培养学生在工业、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.还是实验室的研究生来说都是如此。这包括公开讲座，为理科和非理科专业的学生开发课程，为当地学校的K-8学生提供指导，以及作为全市计划的一部分开展外展活动。

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.