Pressure Tuned Quantum Phase Transitions in Model Systems

*技术摘要*致力于迷人但复杂材料中的量子相变的巨大活动，最常见的是无序，几乎所有都涉及到顺序的间接探测器。理想情况下，人们希望将一种简单的化学计量材料调整到其量子临界点，并直接测量其序参数的消失、量子涨落的影响以及潜在的竞争有序的出现。该项目将低温下的金刚石顶锤单元技术与一组模型系统中的同步x射线散射、磁输运和磁化率相结合，试图分离出量子相变时的关键物理参数和机制。这些包括元素反铁磁体中调制自旋有序的开始，正方形晶格上自旋单重态的基态量子磁性，电荷的有序及其与超导的相互作用，以及相关材料中从绝缘体到金属的转变。从x射线散射到磁传输的各种技术，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。钻石砧座技术的进步应该会影响凝聚态物理学家和地球物理学家。帮助指导为城市学校培训数学和科学教师的新计划是个人的优先事项。*非技术摘要*绝对零度下的相变涉及与有限温度相似的根本不同的物理。这可以包括材料的光学响应、器件的电学特性或存储材料的磁容量。在极低温度的限制下，量子力学发挥了核心作用，改变了为经典转变所制定的普遍反应。这个项目将在四个相关领域探索独特的量子特征：磁性的开始，磁性和超导电性的相互作用，电子电荷的有序，以及绝缘体转化为金属的方式。在每一种情况下，我们都利用了钻石砧座技术的能力，可以获得日常技术之外的压力，并传输高能X射线。广泛的技术，从同步加速器的x射线散射到实验室的电子测量，以及将物理、化学和材料科学应用于这些研究的必要性，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。将研究观点引入教育是另一个重点，包括公开讲座，为科学和非科学专业的学生开发课程，以及在建立国家科学教育推广数据库方面发挥领导作用。

****Technical Abstract****There has been enormous activity devoted to quantum phase transitions in fascinating but complicated materials, most often disordered and almost all involving indirect probes of the order. Ideally, one would like to tune a simple, stoichiometric material to its quantum critical point and directly measure the disappearance of its order parameter, the effects of the quantum fluctuations, and the potential emergence of competing order. This project combines diamond anvil cell technology at cryogenic temperatures with synchrotron x-ray scattering, magnetotransport, and magnetic susceptibility in a set of model systems to attempt to isolate the key physical parameters and mechanisms at quantum phase transitions. These include the onset of modulated spin order in an elemental antiferromagnet, the fundamental quantum magnetism of spin singlets arranged on a square lattice, the ordering of charge and its interplay with superconductivity, and the transition from insulator to metal in a correlated material. The wide array of techniques, from x-ray scattering to magnetotransport, should train students well for careers in industry, the national laboratories, or academia. Advances in diamond anvil cell technology should influence condensed matter physicists and geophysicists alike. Helping guide a new program to train math and science teachers for urban schools is a personal priority.***Non-Technical Abstract****Phase transitions at the absolute zero of temperature involve fundamentally different physics than their finite temperature analogues. This can include the optical response of materials, the electronic character of devices, or the magnetic capacity of storage materials. In the limit of very low temperatures, quantum mechanics plays a central role, altering the universal response that has been mapped out for classical transitions. This project will probe the unique quantum characteristics in four related arenas: the onset of magnetism, the interplay of magnetism and superconductivity, the ordering of electronic charge, and the way in which an insulator can be transformed into a metal. In each we take advantage of the ability of diamond anvil cell technology to access pressures outside of everyday techniques and to transmit high energy x-rays. The wide array of techniques, from x-ray scattering at a synchrotron to electrical measurements in the laboratory, and the necessity to apply physics, chemistry and materials science to these studies, should train students well for careers in industry, the national laboratories, or academia. Bringing research perspectives to education is another emphasis, including public lectures, course development for both science and non-science majors, and a leadership role in developing a national database for science education outreach.