Nuclear Magnetic Resonance Studies of Quantum Criticality in Correlated Electron Materials

非技术摘要：固体中的电子可能会表现出广泛的重要现象，从超导性到磁性。通常，这种行为可以通过控制一些外部参数（如温度、压力或磁场）来调整。该项目通过一系列受控核磁共振（NMR）实验研究了几种关键材料，旨在了解如何调整和控制它们的特性。这种调整可以导致材料行为的戏剧性和意想不到的变化，据信是从一种称为“量子临界”的现象中出现的。这项工作通过在一组精心挑选的材料中探测奇异电子态的性质，推进了对量子临界性的基本理解，并为下一代科学家和工程师的研究生和本科生提供现代物理培训和指导。技术摘要：本研究的目的是对强关联电子材料在量子相附近的行为有更深入的了解过渡。强关联电子材料在新技术方面具有巨大的潜力，但对其相关多体物理学的基本理解仍然是凝聚态物理学中最大的挑战之一。通常，最有趣的科学出现在量子临界点，在那里出现非常规的超导性，非费米液体行为主导正常状态行为。核磁共振（NMR）是研究驱动这些效应的波动的有力工具，但需要受控实验来解开自旋和电荷自由度的影响。该项目利用新的核磁共振技术来探测这些动态下的静水压力和单轴应变互补系统，包括模型重费米子系统表现出费米表面跳跃在量子临界点，和金属与铁四极顺序的本地化f-电子。在这个项目中，几个理论预测正在被测试，这些预测是关于具有多组分手征序参数的自旋三重态超导体的涡核中激发的性质，以及正常状态下的自旋波动如何对单轴应变做出响应。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Abstract: Electrons in solids may exhibit a wide range of important phenomena, ranging from superconductivity to magnetism. Often this behavior can be tuned by controlling some external parameter such as temperature, pressure, or magnetic field. This project investigates several key materials through a set of controlled nuclear magnetic resonance (NMR) experiments with the aim of understanding how to tune and control their properties. Such tuning can lead to dramatic and unexpected changes in the material behavior, believed to emerge from a phenomenon called "quantum criticality". This work advances fundamental understanding of quantum criticality by probing the nature of exotic electronic states within a set of carefully selected materials, and provides modern physics training and mentoring to graduate and undergraduate students for the next generation of scientists and engineers.Technical Abstract: The objective of this proposal is to develop a deeper understanding of the behavior of strongly correlated electron materials near quantum phase transitions. Strongly correlated electron materials hold tremendous potential for new technologies, but a fundamental understanding of their relevant many-body physics remains one of the greatest challenges in condensed matter physics. Often the most interesting science arises at a quantum critical point, where unconventional superconductivity emerges and non-Fermi liquid behavior dominates the normal state behavior. Nuclear magnetic resonance (NMR) is a powerful tool to investigate the fluctuations that drive much of these effects, but requires controlled experiments to disentangle the effects of spin and charge degrees of freedom. This project utilizes new NMR techniques to probe these dynamics under both hydrostatic pressure and uniaxial strain in complementary systems, including a model heavy fermion system exhibiting a Fermi surface jump at a quantum critical point, and a metal with ferro-quadrupolar order of localized f-electrons. Several theoretical predictions are being tested in this project about the nature of the excitations in the vortex cores of a spin-triplet superconductor with a multicomponent chiral order parameter, and how the spin fluctuations in the normal state respond to uniaxial strain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.