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

高温超导铜酸盐掺杂具有强电子相关性的莫特绝缘体。根据CuO(2)平面的掺杂水平(d)和掺杂标志（空穴或电子掺杂）、电子和结构各向异性和无序程度，这些铜酸盐的基态可以出现不同的竞争顺序。这些相互竞争的顺序产生了各种各样的非普遍现象，这些现象掩盖了对铜超导的配对机制的更好理解。该项目的主要目标是揭示各种非普遍现象的物理起源，并确定所有铜中真正普遍存在的特征。技术方法将包括系统的实验研究不同掺杂水平的空穴和电子掺杂铜酸盐(d)，并控制量子杂质的取代，使用新的自制变温高场兼容扫描隧道显微镜（STM）和PI小组的其他辅助表征工具。此外，还对不同模型哈密顿量下的准粒子局域态密度进行了数值计算。由于实验技能的范围和参与者完成任务所需的理论知识的深度，本研究具有重要的教育价值。该研究的成功完成可以科学地推进当前对铜超导和其他强相关电子系统中竞争顺序配对机制的理解，而技术上STM仪器专业知识可以有利于新型纳米级材料和器件的研究。自1986年发现高温超导现象以来，尽管对高温超导现象的研究取得了很大进展，但其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，不同的铜超导体家族中可能存在各种各样的低温物理相。本研究项目旨在通过研究铜酸盐中不同的物理相如何发生来揭开高温超导的神秘面纱，并确定所有铜酸盐中真正普遍存在的导致高温超导的特征。实验方法包括使用自制的可变温度高场兼容扫描隧道显微镜（STM）和加州理工学院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。STM测量可以提供有关铜的重要信息，具有原子尺度的空间分辨率。除实验外，还将进行计算机建模，以便与实验数据进行比较。由于实验技能的范围和参与者完成任务所需的理论知识的深度，本研究具有重要的教育价值。该项目的成功完成将促进铜超导体的理论认识和商业应用。为此项目开发的STM仪器可以进一步有利于纳米科学技术新兴领域中新型纳米级结构和器件的表征。

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.