A Novel Gap Spectroscopy Tool and Discovery of New Nodal Superconductors

高温超导体由于其高转变温度和奇异的新相关电子态，在量子信息处理等变革性应用方面显示出巨大的潜力。该项目的目标是发现新的非常规超导材料类别，并使用首席研究员发现的一种新的实验技术来检查它们是否存在非常规超导性。该项目培养具有物理和工程背景的研究生，以发现凝聚态物理研究前沿的新材料和现象。学生还参与国际研究，在德国卡尔斯鲁厄理工学院的功能纳米结构中心进行部分博士研究。美国和德国的实验室相互补充，从而提高了研究生的教育经验。首席研究员有扩大弱势群体参与的历史，并参与了招募更多弱势学生的外展活动。该项目旨在为凝聚态研究人员建立一种新的实验技术，建立新的伙伴关系、合作关系和设施，从而影响超导材料和应用领域的前景。技术摘要：该奖项来自材料研究部凝聚态物理项目，支持马里兰大学的一个项目，该项目致力于发现具有新特性的新型超导材料，并进一步将各向异性非线性迈斯纳效应光谱方法改进为一种广泛有用的技术，为正在进行的关于非常规超导体配对机制的辩论做出重要贡献。首席研究员对各向异性非线性迈斯纳效应光响应的发现有助于加速发现具有非平凡和奇异性质的超导材料。该方法依赖于各向异性非线性迈斯纳效应和安德烈夫束缚态的存在，来创建超导体的非线性电动力响应图像，以说明超导间隙节点方向。该方法对体特性（通过超流体各向异性非线性响应）和表面特性（通过测量与非常规序参量相关的Andreev束缚态）都很敏感。将超导薄膜制成紧凑的自共振螺旋结构，在射频范围内近共振激发，用聚焦激光束扰动扫描。在低温下，谐振器的反应性和电阻性中方向相关的非线性会产生光响应，从而绘制出超导体费米表面上节点或与这些节点相关的束缚态的方向。该方法在已知的节点超导体上得到了证明，因此下一步是通过将该方法扩展到单晶和无图案薄膜上来发现新的节点超导体。共同研究小组培育新的超导材料，研究小组在内部进行实验，并与德国卡尔斯鲁厄的一个小组合作，以发现新的节点超导体。发现的新材料应该具有变革性应用的潜力，包括新形式的超导电子学或敏感的单光子探测器。研究结果透过出版物、国际会议的演讲和海报、一个研究网站、一个解释如何用最少的设备建立非线性迈斯纳效应实验的教程网站，以及PI、合作PI和学生继续开展的外展活动来传播。

Non-Technical AbstractBecause of their high transition temperatures and exotic new correlated electronic states, high temperature superconductors show a great potential for transformative applications, such as quantum information processing. The objective of this project is to discover new classes of unconventional superconducting materials and to examine them for evidence of unconventional superconductivity using a new experimental technique that the principal investigator discovered. The project trains graduate students with backgrounds in physics and engineering to discover new materials and phenomena at the forefront of condensed matter physics research. The students also participate in international research, carrying out part of their Ph.D. research at the Center for Functional Nanostructures at the Karlsruhe Institute of Technology in Germany. The US and German laboratories complement each other, thus enhancing the educational experience for the graduate students involved. The principal Investigator has a history of broadening the participation of underrepresented groups and is involved in outreach activities to recruit more underrepresented students. This project is establishing a new experimental technique of interest to condensed matter researchers, creating new partnerships, collaborations, and facilities that impact the landscape of the superconducting materials and applications fields. Technical AbstractThis award from the Condensed Matter Physics Program in the Division of Materials Research supports the University of Maryland with a project focused on the quest to discover new superconducting materials with new properties, and to further refine the anisotropic nonlinear Meissner effect spectroscopy method into a broadly useful technique that contributes significant results to the ongoing debates about the pairing mechanism in unconventional superconductors. The principal investigator's discovery of the anisotropic nonlinear Meissner effect photoresponse helps to speed up the discovery of superconducting materials with nontrivial and exotic properties. The method relies on the anisotropic nonlinear Meissner effect, and the presence of Andreev bound states, to create images of the nonlinear electrodynamic response of the superconductor that illustrate the superconducting gap nodal directions. The method is sensitive to both bulk properties (through the superfluid anisotropic nonlinear response) and surface properties (through measurement of Andreev bound states associated with the unconventional order parameter). A superconducting thin film is patterned into a compact self-resonant spiral structure, excited near resonance in the radio-frequency range, and scanned with a focused laser beam perturbation. At low temperatures, direction-dependent nonlinearities in the reactive and resistive properties of the resonator create photoresponse that maps out the directions of nodes, or of bound states associated with these nodes, on the Fermi surface of the superconductor. The method was demonstrated on a known nodal superconductor, so the next step is to discover new nodal superconductors by extending the method to work on single crystals and un-patterned thin films. The co-PI grows the new superconducting materials and the PI performs the experiments both in-house and in collaboration with a group in Karlsruhe, Germany, to discover new nodal superconductors. The new materials discovered should have potential for transformative applications, including new forms of superconducting electronics, or sensitive single-photon detectors. The results are disseminated through publications, talks and posters at international conferences, a research web site, a tutorial web site explaining how to set up a nonlinear Meissner effect experiment with minimal equipment, and continuation of the outreach activities by the PI, co-PI and students.