ARPES Study of Electronic Evolution from Mott Insulators to Novel Superconductors

该个人研究者奖将支持对新型超导体电子结构演变的持续角分辨光发射（ARPES）研究。本项目研究的材料包括超导铜酸盐、钌酸盐和钴酸盐。它们都是二维氧化物，当掺杂离开半填充的莫特绝缘体状态时就会变成超导。这些材料的非常规超导性是凝聚态物理中最重要的课题之一。此外，在某些掺杂条件下，还可能产生电荷（自旋）有序态等奇异相。这些状态的物理性质也非常重要。本项目涉及在广泛的掺杂范围内对这些材料进行系统的ARPES研究。它将帮助我们理解不同相的基本电子结构。除了波段色散和费米表面的“传统”测量外，在这些强相关材料中至关重要的多体相互作用也将通过高分辨率ARPES进行研究。更好地理解掺杂Mott绝缘体中的电子结构将极大地促进我们对Mott物理、新型超导性、低维性、量子临界性和非费米液体物理的认识。该项目还将通过向高中生、本科生、研究生和博士后介绍令人兴奋的新材料、尖端技术和基础凝聚态物理，对他们的教育产生重大影响。传统绝缘体的最外层电子轨道要么是空的，要么是完全填满的，而所谓的“莫特”绝缘体的最高轨道是部分填满的。它们的绝缘性来自于电子之间的强相互作用。更有趣的是，当额外的电子从莫特绝缘体中加入或移除时，它们会表现出许多不寻常的物理现象。一些这样的“掺杂”材料在放置于磁场中时，其电阻表现出非常大的变化。另一些则变成超导，失去所有电阻，温度高于液氮——即所谓的高温超导体。几种表现出新型超导性的掺杂莫特绝缘体是本实验项目的重点。光电发射技术是通过吸收紫外光从固体样品中敲出电子。研究发射的电子以获得它们在固体内部的构型信息，即材料的电子结构。电子结构对于理解许多材料的性质至关重要。提出的系统光电发射研究，在广泛的掺杂范围内，将有助于我们了解这些材料中许多外来相的潜在电子结构。该项目的成功将极大地促进我们对高温超导和莫特物理学的理解。更好地了解这些新材料的物理性质将有助于发挥它们的应用潜力。该项目还将通过向学生介绍令人兴奋的新材料、尖端技术和先进物理，对学生的教育产生重大影响。他们将获得参与国家设施研究的经验。

This individual investigator award will support continued angle-resolved photoemission (ARPES) studies on the evolution of the electronic structure of novel superconductors. The materials studied in this project include superconducting cuprates, ruthenates, and cobaltates. All of them are 2D oxides that become superconducting when doped away from half-filled Mott insulator states. Unconventional superconductivity in these materials is one of the most important topics in condensed matter physics. In addition, other exotic phases, such as charge (spin) ordered states, may develop at certain doping. The physics of these states are of great importance as well. This project involves systematic ARPES studies on these materials over wide doping ranges. It will help us to understand the underlying electronic structure of the different phases. Besides the 'traditional' measurements of band dispersion and Fermi surface, many-body interactions, which are crucial in these strongly correlated materials, will be also investigated by high-resolution ARPES. A better understanding of the electronic structure in doped Mott insulators will significantly advance our knowledge of Mott physics, novel superconductivity, low dimensionality, quantum criticality, and non-Fermi liquid physics. This project will also make a significant impact on the education of high school students, undergraduate, graduate students, and post-docs by introducing them to exciting new materials, cutting-edge techniques, and fundamental condensed matter physics. Unlike traditional insulators that have either empty or completely filled outermost electron orbitals, the so-called "Mott" insulators have highest orbitals that are partially filled. Their insulating nature comes from strong interactions among the electrons. More interestingly, when extra electrons are added or removed from the Mott insulators, they exhibit many unusual physical phenomena. Some such "doped" materials show a very large change in their electrical resistance when placed in a magnetic field. Others become superconducting, lose all electrical resistance, above the temperature of liquid nitrogen - the so-called high temperature superconductors. Several doped Mott insulators, which exhibit novel superconductivity, are the focus of this experimental project. The technique of photoemission is used to knock out electrons from a solid sample through the absorption of ultraviolet light. The emitted electrons are studied to gain information about their configuration inside the solid, the electronic structure of the material. The electronic structure is crucial for the understanding of many of the materials' properties. The proposed systematic photoemission studies, over wide doping ranges, will help us understand the underlying electronic structure of many exotic phases in these materials. The success of this project will significantly advance our understanding of high temperature superconductivity and Mott physics in general. A better understanding of the physics of these novel materials will be helpful in realizing their application potentials. This project will also make a significant impact on the education of students by introducing them to exciting new materials, cutting-edge techniques, and advanced physics. They will gain the experience of participating in research at national facilities.