Quasiparticle Spectroscopic Studies of the Pairing State and Competing Orders in Hole- and Electron-Doped Cuprate Superconductors

高温超导铜酸盐是掺杂Mott绝缘体，具有很强的电子相关性。根据掺杂水平(D)和掺杂(空穴或电子掺杂)在CuO(2)面上的符号、电子和结构的各向异性以及无序，这些铜酸盐的基态可能会出现不同的竞争顺序。这些相互竞争的秩序导致了各种非普遍现象，掩盖了对铜酸盐超导电性配对机制的更好理解。该项目的主要目标是揭开各种非普遍现象的物理根源，并确定在所有铜矿中真正普遍存在的特征。该技术方法将使用一种新的自制变温高场兼容扫描隧道显微镜(STM)和PI小组中的其他辅助表征工具，对不同掺杂水平(D)和受控取代量子杂质的空穴和电子掺杂铜酸盐进行系统的实验研究。此外，还将对不同模型哈密顿量的准粒子局域态密度(LDOS)进行数值计算。所提出的研究具有重要的教育价值，因为参与者需要广泛的实验技能和深入的理论知识来完成任务。这项研究的成功完成可以从科学上促进目前对铜酸盐超导电性配对机制和其他强关联电子系统中相互竞争的有序的理解，而STM仪器的专业知识在技术上可以帮助研究新型纳米材料和器件。自1986年发现高温超导以来，高温超导的物理原因仍然是一个谜。缺乏完整的理论理解的主要原因是，通过简单地调整这些材料的化学性质，可以在不同家族的铜酸盐超导体中存在各种低温物理相。这个研究项目旨在通过研究不同的物理相如何在铜酸盐中发生来揭开高温超导的神秘面纱，并确定所有导致高温超导的铜酸盐中真正普遍存在的特征。实验方法包括使用自制的变温高场兼容扫描隧道显微镜(STM)和加州理工大学PI小组的其他辅助表征工具对不同的铜酸盐进行系统研究。扫描隧道显微镜的测量可以提供有关原子尺度空间分辨率的铜酸盐的重要信息。除实验外，还将进行计算机模拟，以与实验数据进行比较。所提出的研究具有重要的教育价值，因为参与者需要广泛的实验技能和深入的理论知识来完成任务。该项目的顺利完成将促进铜酸盐超导体的理论理解和商业应用。为这一项目开发的扫描隧道显微镜仪器可以进一步有助于在新兴的纳米科学与技术领域对新型纳米结构和器件的表征。

High-temperature superconducting cuprates are doped Mott insulators with strong electronic correlation. Depending on the doping level (d) and the sign of the dopant (hole- or electron-doping) in the CuO(2) planes, the electronic and structural anisotropies, and disorder, different competing orders can emerge in the ground state of these cuprates. These competing orders give rise to various non-universal phenomena that have masked better understanding for the pairing mechanism of cuprate superconductivity. The primary objective of this project is to unravel the physical origin of various non-universal phenomena and to identify truly ubiquitous characteristics among all cuprates. The technical approach will involve systematic experimental studies of hole- and electron-doped cuprates of different doping levels (d) and with controlled substitutions of quantum impurities, using a new homemade variable-temperature high-field-compatible scanning tunneling microscope (STM) and other auxiliary characterization tools in the PI's group. In addition, numerical computations of the quasiparticle local density of states (LDOS) for different model Hamiltonians will be performed. The proposed research is of significant educational value because of the range of experimental skills and the depth of theoretical knowledge required of the participants to accomplish the tasks. Successful completion of the research can scientifically advance current understanding of the pairing mechanism of cuprate superconductivity and of the competing orders in other strongly correlated electronic systems, whereas technologically the STM instrumentation expertise can benefit research on novel nano-scale materials and devices.The physical cause for the occurrence of high-temperature superconductivity (HTS) in the cuprate superconductors remains a mystery despite substantial research progress since the discovery of HTS in 1986. The primary reason for the lack of complete theoretical understanding is due to the variety of low-temperature physical phases that can exist in different families of cuprate superconductors upon simple "tuning" of the chemical properties of these materials. This research project intends to unveil the mystery of HTS by investigating how different physical phases occur in the cuprates, and to identify the truly ubiquitous characteristics among all cuprates that are responsible for HTS. The experimental approach involves systematic studies of different cuprates using a homemade variable-temperature high-field-compatible scanning tunneling microscope (STM) and other auxiliary characterization tools in the PI's group at Caltech. The STM measurements can provide important information about the cuprates with atomic-scale spatial resolution. In addition to the experiments, computer modeling will be performed for comparison with experimental data. The proposed research is of significant educational value because of the range of experimental skills and the depth of theoretical knowledge required of the participants to accomplish the tasks. Successful completion of this project can advance the theoretical understanding and commercial applications of cuprate superconductors. The STM instrumentation developed for this project can further benefit the characterization of novel nano-scale structures and devices in the emerging field of nano-science & technology.