Center for Correlated Electron Systems

Electronic Structure

Electronic Structures Group

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, such as Rashba, Dresselhaus and catalytic reaction. We also investigate quasi-two dimensional materials - layered 3D materials in which layers are weakly coupled through the weak van der Waals force. We especially investigate the electronic structures of transition metal dichalcogenides (TMDCs), possibly useful for electronic device applications.
Superconductivity Team
Since the discovery of the cuprate, a lot of efforts to understand the mechanism of high temperature superconductor have been made. Numerous studies have found a number of clues to the mechanism of superconductivity, but they are not yet fully understood. The aim of this research group is to understand the mechanism through the angle resolved photoemisson spectroscopy (ARPES) which gives critical clue by visualizing the electronic structure directly. Among various topics in SCs, our current focus is finding the origin of the nematic phase that may provide critical clues on superconductivity mechanism.
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.
Prof. Changyoung Kim's photo
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
Physcial Review Letters 121 , 1086602 (2018)
Large anomalous Hall current induced by topological nodal lines in a ferromagnetic van der Waals semimetal
Nature Materials 17 , 794-799 (2018)
Electron number-based phase diagram of Pr1-xLaCexCuO4-δ and possible absence of disparity between electron- and hole-doped cuprate phase diagrams
Physical Review Letters 118 , 137001 (2017)
Possible role of bonding angle and orbital mixing in iron pnictide superconductivity: Comparative electronic structure studies of LiFeAs and Sr2VO 3FeAs
Physical Review B 92 , 041116 (2015)
Existence of orbital order and its fluctuation in superconducting Ba(Fe1-xCox)2As2 single crystals revealed by x-ray absorption spectroscopy
Physical Review Letters 111 , 217001 (2013)
Microscopic mechanism for asymmetric charge distribution in Rashba-type surface states and the origin of the energy splitting scale
Physical Review B 88 , 205408 (2013)
Main Equipment
In situ spin and angle resolved photoemission cluster system

In situ spin and angle resolved photoemission cluster system

The main experimental technique used in our research is angle resolved photoemission spectroscopy (ARPES). ARPES can directly measure the electronic structure of material, which means that you can discover the electronic origin of various physical phases. We currently have total 4 ARPES systems. 6eV-laser and discharge lamp based ultra-high resolution ARPES and spin resolved ARPES with in situ magnetization cluster systems can support in situ sample growth capability using pulsed laser deposition and molecular beam epitaxy methods. Moreover, we have 11eV-laser and time of flight analyzer based ARPES systems which also support in situ sample preparation in globe box. We are constructing 4th system for laser based time resolved-ARPES and Second Harmonic Generation (SHG) system in collaboration with the world leading facility, Institute for Solid State Physics (ISSP), Japan. With these fascinating ARPES systems, we are trying to do the world top class leading researches in condensed matter physics and material science.