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，但铜酸盐超导电性的配对机制到目前为止仍然难以捉摸。铜酸盐超导体是一种掺杂的反铁磁性Mott绝缘体，具有很强的电子相关性。根据掺杂程度的不同，除了超导电性外，基态还可能由各种竞争顺序组成。竞争有序的存在自然会导致量子临界性和量子涨落，从而显著影响低能激发并导致大量的非常规现象。尽管相互竞争的顺序产生了明显的影响，但相互竞争的顺序是否与超导电性有关仍不清楚。解决这个问题的一种可能的方法是将铜酸盐与一种新的超导体--铁硫化物(最高转变温度约为52K)进行比较。这些铁陨石与铜酸盐显示出有趣的相似之处和对比。因此，对这两个系统的平行研究可能会对超导体中的对子形成这一基本问题提供有用的见解。该技术方法将重点研究铜酸盐和铁基超导体的原子分辨准粒子隧道谱作为磁场的函数，使用自制的高场低温扫描隧道显微镜和本小组建立的用于数据分析和建模的数值工具。其目的是为这两个系统中的低能激发建立一个全面的现象学，从而找到非常规超导体中库珀配对的指导原则。此外，开展研究所需的培训涉及先进技术和理论知识，因此对年轻科学家的教育是有效的。非技术摘要：该奖项由2009年《美国复苏和再投资法案》(公法111-5)资助。1986年在一类被称为铜酸盐的氧化物材料中发现高温超导电性，模拟了世界范围内紧张的研究工作，因为人们对其潜在的广泛应用寄予了很高的期望。尽管在科学和技术上都取得了很大进展，但高温超导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。2008年发现了一类新的超导体，被称为铁系超导体(最高转变温度约为52K)。这些新的铁基超导体与铜酸盐有有趣的相似之处和反差。这一研究项目的主要目的是对铜酸盐和铁-磷酸盐超导体系的物理性质进行平行研究和比较。这些研究的目的是为制造具有更高转变温度和更好物理性能的超导体的方法提供见解，从而促进基于超导材料的更好的应用。此外，开展这一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.