ARPES Study of Electronic Evolution from Mott Insulators to Novel Superconductors

Boston College, Chestnut Hill MA

Investigators

Abstract

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.