Spatially Resolved Quasiparticle Tunneling Spectroscopic Studies of Cuprate and Iron-Based High-Temperature Superconductors

技术摘要：该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。尽管自1986年以来取得了很大进展，但铜氧化物超导性的配对机制至今仍然难以捉摸。铜氧化物超导体是一种掺杂的反铁磁Mott绝缘体，具有很强的电子关联。取决于掺杂水平，基态可以由除了超导性之外的各种竞争顺序组成。竞争有序的存在自然导致量子临界和量子涨落，这显著影响低能激发并导致许多非常规现象。尽管与竞争秩序相关的明显效应，但竞争秩序是否与超导性有关仍不清楚。解决这个问题的一个可能的方法是将铜酸盐与一类新的超导体，铁磷属元素化物（最高转变温度约为52 K）进行比较。这些铁磷族化合物与铜酸盐表现出有趣的相似性和对比性。因此，这两个系统的平行研究可能会提供有用的见解对超导体中形成的基本问题。技术方法将侧重于调查原子分辨的准粒子隧道光谱的铜酸盐和铁基超导体的磁场的功能，使用自制的高场低温扫描隧道显微镜和数字工具建立在这个组的数据分析和建模。我们的目标是发展一个全面的现象学的低能量激发在这两个系统中，从而找到库珀配对在非常规超导体的指导原则。此外，开展研究所需的培训涉及先进的技术和理论知识，因此对年轻科学家的教育是有效的。非技术摘要：该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。1986年在一类被称为铜酸盐的氧化物材料中发现高温超导性，由于对潜在的广泛应用寄予很高的期望，因此模拟了世界范围内的紧张研究工作。尽管科学和技术已经取得了很大的进步，但高温超导性发生的物理原因仍然未知。此外，这些材料的复杂性使得它们的应用比最初预期的更具挑战性。在2008年发现了一类新的超导体，称为铁磷属元素化物（最高转变温度~ 52 K）。这些新的铁基超导体揭示了与铜酸盐有趣的相似性和对比。本研究计划的主要目的是对铜酸盐和铁磷族化合物超导体系的物理性质进行平行研究和比较。这些研究的目的是提供见解，使超导体具有更高的转变温度和更好的物理性能，从而推进基于超导材料的更好的应用。此外，开展该研究项目所需的培训涉及各种先进技术和理论知识，因此对年轻研究人员的教育是有效的。

Technical Abstract:This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The pairing mechanism for cuprate superconductivity remains elusive to date despite much progress since 1986. Cuprate superconductors are doped anti-ferromagnetic Mott insulators with strong electronic correlation. Depending on the doping level, the ground state may consist of various competing orders besides superconductivity. The existence of competing orders naturally leads to quantum criticality and quantum fluctuations, which significantly affects the low-energy excitations and results in numerous unconventional phenomena. Despite apparent effects associated with competing orders, whether competing orders are relevant to superconductivity remains unclear. One possible approach to addressing this issue is to compare the cuprates with a new class of superconductors, the iron pnictides (with a maximum transition temperature ~ 52 K). These iron pnictides exhibit interesting similarities and contrasts to the cuprates. Therefore, parallel studies of both systems may provide useful insights into the fundamental issue of pair formation in superconductors. The technical approach will focus on investigating the atomically resolved quasiparticle tunneling spectra of both cuprate- and iron-based superconductors as functions of magnetic fields using a homemade high-field cryogenic scanning tunneling microscope and the numerical tools established in this group for data analysis and modeling. The objective is to develop a comprehensive phenomenology for the low-energy excitations in both systems, thereby finding the guiding principles for Cooper pairing in unconventional superconductors. Additionally, the trainings required for conducting the research involve advanced technologies and theoretical knowledge, and are therefore effective for the education of young scientists.Non-Technical Abstract:This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The discovery of high-temperature superconductivity in a class of oxide materials known as cuprates in 1986 had simulated intense worldwide research efforts because of high expectations for potentially a wide range of applications. Although much progress has been made both scientifically and technologically, the physical cause for the occurrence of high-temperature superconductivity remains unknown. Moreover, the complexity of these materials makes applications of them far more challenging than originally anticipated. In 2008 a class of new superconductors, known as the iron pnictides (with a maximum transition temperature ~ 52 K), was discovered. These new iron-based superconductors reveal interesting similarities and contrasts to the cuprates. The primary thrust of this research project is to conduct parallel studies and comparison of the physical properties of both cuprate and iron-pnictide superconducting systems. The objective of these studies is to provide insights into means of making superconductors with higher transition temperatures and better physical properties, thereby advancing better applications based on superconducting materials. Additionally, the training required for conducting this research project involves a wide variety of advanced technologies and theoretical knowledge, and are therefore effective for the education of young researchers.