Electronic Structure

Electronic Structures Group  /  Prof. Changyoung Kim  

     The Electronic Structure Group, led by Prof. Changyoung Kim, is the third group to be established within the IBS Center for Correlated Electron Systems. The research of our group covers electronic structure studies of correlated electron systems such as high Tc superconductors, transition metal oxides and materials with strong spin-orbit coupling (SOC), with a focus on orbital degrees of freedom. The group currently consists of three teams of ‘OAM/2D materials’, ‘Transition metal oxides’ and ‘Superconductivity’ teams. 

     The Electronic Structures group uses novel and advanced spectroscopic techniques to study the electronic structures of solids. Our main tool is angle resolved photoelectron spectroscopy (ARPES) which provides direct information on the electronic structures of materials such as band dispersions and Fermi surfaces. State of the art ARPES systems at various synchrotron facilities around the world are used. We have home-lab based ARPES systems with pulsed laser deposition (PLD) and molecular epitaxy growth (MBE) for ARPES on in situ sample growth. We also plan to construct a laser-based ultra-high resolution ARPES system to investigate dynamic properties and spin-resolved ARPES for spin structure studies.

Orbital Angular Momentum (OAM) / 2D Materials Team
The orbital angular momentum (OAM)/2D materials team focuses on novel physical phenomena stemming from orbital degrees of freedom on surfaces and interfaces. They include Rashba, Dresselhaus and catalytic reaction. We wish to understand these phenomena by investigating the electronic structures. 

Superconductivity Team
The superconductivity team investigates the electronic structure of various superconductors (SC) to understand the superconducting mechanism. Among various SCs, our current focus is on iron-based superconductors (FeSC) which was first discovered in 2008. Two main research scopes are described below. 

Oxides Team
The oxide materials are abundant in Nature because oxygen is a main ingredient of our atmosphere and has strong chemical reactivity. Among them, transition-metal and rare-earth oxides have attracted much attention because of their novel physical properties that can be controlled by external parameters such as electromagnetic fields, temperature, pressure. Most of them are electrically insulating but some show fascinating electrical properties that are believed to originate from strong electron-electron correlation in an unfilled d- or f-shell. Our goal is to understand their electronic structures, which are not tractable by the density functional theory, using various electron spectroscopy tools such as ARPES, XPS, XAS, and IPES. 

[Selected Publications]                            

* Experimental observation of hidden Berry curvature in inversion-symmetric bulk 2H−WSe2
   Physcial Review Letters 121 , 186401(2018) 
* Intrinsic spin and orbital Hall effects from orbital texture
* Large anomalous Hall current induced by topological nodal lines in a ferromagnetic van der Waals semimetal
* Electron number-based phase diagram of Pr1-xLaCexCuO4-δ and possible absence of disparity between electron- and hole-doped cuprate phase diagrams
* Possible role of bonding angle and orbital mixing in iron pnictide superconductivity: Comparative electronic structure studies of LiFeAs and Sr2VO 3FeAs
* Existence of orbital order and its fluctuation in superconducting Ba(Fe1-xCox)2As2 single crystals revealed by x-ray absorption spectroscopy
* Microscopic mechanism for asymmetric charge distribution in Rashba-type surface states and the origin of the energy splitting scale