Controlled variations of quantum phases observed by NMR

在电子材料中观察到当前凝聚态物理中广泛的感兴趣的现象，其中必须考虑相互作用以进行适当的描述。这些相关性如何显现取决于多个参数，这些参数可用于调整复杂的系统。例如，在极低温度下观察到的物质状态可以通过外部参数来控制，如磁场、应变或载流子掺杂。执行这种调优是为了研究物质的新的和未表征的状态，控制一种或另一种状态内的物理特性，提供现有理解失效的地方，并通过优化来研究应用的潜力。在这个项目中，核磁共振（NMR）以多种方式应用于受可变磁场和单轴应变影响的选定系统。具体的目标范围从研究其他难以接近的物质状态的性质，到澄清用其他方法无法解决的问题。使用核磁共振是因为它提供了一个了解局部电子环境的窗口。研究生和本科生都接受低温、射频和模拟技术方面的培训，并有机会与位于美国和国外用户设施（如塔拉哈西的国家磁实验室）的研究小组进行培训和合作。除了由这些合作发起的研究小组之间的科学、技术和硬件转移之外，学生们还可以通过与其他领域的科学家互动，以及通过对设施的长期访问，获得互补的专业知识。技术摘要：本项目采用固态磁共振技术来解决与准二维超导体和受挫量子磁体相关的问题。该方法将核磁共振（NMR）与极端条件的不同组合相结合，特别是单轴应变、高磁场和温度范围小于1 K。目的是研究诱导相和激发的性质。核磁共振非常适合这项任务，因为该技术通过超精细相互作用和核与电场梯度的四极耦合对局部磁和电荷环境普遍敏感。应变法可在原位连续变化，具有广泛的应用前景；在这里，它将被用于一种长期被认为是手性p波超导体的化合物。通过输运和敏感性研究，证明了临界温度的剧烈非单调变化。核磁共振实验将告知应变引起的正常和超导状态的变化，包括费米表面拓扑结构和状态密度的变化，预期分裂超导转变的识别，或不同超导阶之间的转变。高磁场将被用来稳定和研究准二维化合物中非均匀超导的物理性质，在准二维化合物中，由于异常大的电子结构各向异性，避免了超导态的轨道抑制。

Non-technical abstractA wide range of phenomena of current interest in condensed matter physics are observed in electronic materials where interactions must be taken into account for a proper description. How those correlations are manifest depends on multiple parameters, which can be used to tune the complex systems. For example, the state of matter observed in very low temperatures can be controlled by an external parameter, like magnetic field, strain or carrier doping. Such tuning is performed to investigate new and uncharacterized states of matter, to control the physical properties within one state or another, to provide insight where prevailing understandings break down, and to investigate the potential for applications through optimization. In this project, nuclear magnetic resonance (NMR) is applied in versatile ways to selected systems subjected to variable magnetic fields and uniaxial strain. The specific objectives range from studies of the properties of otherwise inaccessible states of matter, to clarifying questions unresolved by other means. NMR is used because it provides a window into the local electronic environment. Both graduate and undergraduate students are trained in cryogenic, radiofrequency, and simulation technologies, with opportunities to train and collaborate with research groups located at user facilities in the United States and abroad, such as the National MagLab in Tallahassee. In addition to the transfer of science, technology and hardware between research groups initiated by these collaborations, the students benefit from exposure to complementary expertise by way of interactions with scientists working in other areas, and through extended visits to facilities. Technical abstractThis project employs solid state magnetic resonance techniques to address questions associated with quasi-two dimensional superconductors and frustrated quantum magnets. The approach integrates nuclear magnetic resonance (NMR) with different combinations of extreme conditions, specifically uniaxial strain, high magnetic fields, and temperatures ranging to less than 1 K. The objective is to study the nature of induced phases and excitations. NMR is well-suited for this task since the technique is generally sensitive to the local magnetic and charge environment through the hyperfine interaction and nuclear quadrupolar coupling to the electric field gradient. The strain method has potential for broader application since it can be varied continuously in situ; here it will be employed in a compound long-considered a chiral p-wave superconductor. Through transport and susceptibility studies, dramatic, non-monotonic changes in the critical temperature were demonstrated. NMR experiments will inform as to strain-induced changes to both normal and superconducting states, including changes to Fermi surface topology and density of states, identification of an anticipated split superconducting transition, or a transition between different superconducting orders. High magnetic fields will be utilized to stabilize and study the physical properties of inhomogeneous superconductivity in a quasi-2D compound for which where orbital suppression of the superconducting state is avoided as a result of uncommonly large electronic structure anisotropy.