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Angle-resolved photoemission spectroscopy studies of electron-electron interactions in graphene
황춘규,강해용 한국물리학회 2021 Current Applied Physics Vol.30 No.-
Graphene is an emergent research topic that has attracted a huge amount of research interest ever since its experimental demonstration as a two-dimensional realization of Dirac fermions in 2005. In subsequent years, the research on graphene has rapidly expanded its field not only due to the new paradigm to study relativistic high energy physics in a condensed matter, but also due to its potential in the application for next generation devices. Most of the novel phenomena observed so far in graphene are attributed to its low-energy excitations, which is described by those of relativistic Dirac fermions. This article reviews recent progress in angle-resolved photoemission spectroscopy studies of electron-electron interactions in graphene.
황춘규,강민희,Hwang, Choongyu,Kang, Minhee 한국진공학회 2018 진공 이야기 Vol.5 No.2
The research field of graphene has been rapidly expanded ever since its first experimental realization of Dirac fermions in 2005, due to the fundamental importance in physics as a new paradigm for relativistic condensed matter physics as well as a potential building block for next generation device applications. Most of the intriguing physics observed so far in graphene can be traced to its peculiar electron band structure, which is in analogy with relativistic Dirac fermions. This article reviews recent progress in graphene research that has been done using angle-resolved photoemission technique, the most direct probing tool of the electron band structure. In particular, we discuss a few examples of novel properties so far explored ranging from the basic electron band structure to complicated many-body interactions.
황진웅,황춘규,정낙관,A. D. N’Diaye,A. K. Schmid,Jonathan Denlinger 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.4
The interface between graphene and a ferromagnetic substrate has attracted recent research interests due to its potential for spintronic applications. We report an angle-resolved photoemission spectroscopy study on the interface between graphene and cobalt epitaxially grown on a tungsten substrate. We find that the electron band structure of the interface exhibits clear discontinuities at the crossing points with cobalt 3d bands. These observations indicate strong hybridizations between the electronic states in the interface and provide an important clue to understand the intriguing electromagnetic properties of the graphene/ferromagnet interface.
주현정,김규,황춘규 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
Topological properties of a matter are one of the main streams in the recent study of condensed matters. Especially, several materials have been explored to find a topological Dirac state that is protected by symmetries. Using ARPES, we present the electron band structure of Cu<sub>2</sub>Si on Si(111) that exhibits topological Dirac nodal-lines protected by mirror reflection symmetry. We also discuss low-energy excitations of the Dirac state that is possibly described as the marginal Fermi liquid.
Observation of a Temperature-Induced Phase Transition on the Si(5 5 12) Surface
S. H. Uhm,정진욱,황춘규,S. Y. Shin,H. S. Kim 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
We have investigated the electrical property of the high-index Si(55 12) surface as a function of substrate temperature. We find that the surface undergoes a structural phase transition accompanying an electrical phase transition from a semiconducting 2 × 1 phase at room temperature (RT) to a metallic 1 × 1 phase above a transition temperature Tc = 520 ℃. Our high-resolution electron-energy-loss spectroscopy data show a band gap with Eg = 0.34 eV for the semiconducting 2 × 1 phase at RT and a Drude tail for the metallic 1 × 1 phase at high temperature. Our low-energy electron-diffraction observation exhibits a structural phase transformation from a 2 × 1 phase characterized by streaks along the [665] direction to a well-defined 1 × 1 with no such streaks. No prominent electronic state that crosses the Fermi level, however, is found for T ≥ Tc although a slightly enhanced intensity at the Fermi level is evident near the Γ point. We attribute the transition to an order-disorder transition rather than a period-doubling Peierls-type transition because the streaks signaling disorder disappear completely for the 1 × 1 phase, T ≥ Tc.
Surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2
김동섭,기정연,이지은,Liu Yu,김영학,김남동,황춘규,김원동,Petrovic Cedomir,이동렬,Jang Chaun,류혜진,최준우 한국물리학회 2021 Current Applied Physics Vol.30 No.-
We investigate the surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2, a material widely utilized for spintronic applications. While known for its relative air-insensitivity, exposure to air during the handling process (e.g. device or heterostructure fabrication) can lead to reduction or disappearance of its magnetic signal. Comparison of x-ray absorption and x-ray magnetic circular dichroism spectra between pristine and air-exposed Fe3-xGeTe2 confirm a naturally oxidized surface layer on the material. The surface oxide layer has predominantly Fe3+ content. X-ray absorption spectroscopy done on micron-sized exfoliated Fe3-xGeTe2 flakes reveal that the change in the surface chemical properties can be quite significant for thin flakes. The surface modulation of Fe3- xGeTe2 can lead to inaccuracies in characterizing its interfacial magnetic and spin transport properties, and complicate device and heterostructure fabrication processes.
Gapped Nearly Free-Standing Graphene on an SiC(0001) Substrate Induced by Manganese Atoms
황진웅,이지은,강민희,박병규,Jonathan Denlinger,모성관,황춘규 한국진공학회 2018 Applied Science and Convergence Technology Vol.27 No.5
The electron band structure of manganese-adsorbed graphene on an SiC(0001) substrate has been studied using angleresolved photoemission spectroscopy. Upon introducing manganese atoms, the conduction band of graphene, that is observed in pristine graphene indicating intrinsic electron-doping by the substrate, completely disappears and the valence band maximum is observed at 0.4 eV below Fermi energy. At the same time, the slope of the valence band decreases by the presence of manganese atoms, approaching the electron band structure calculated using the local density approximation method. The former provides experimental evidence of the formation of nearly free-standing graphene on an SiC substrate, concomitant with a metal-to-insulator transition. The latter suggests that its electronic correlations are efficiently screened, suggesting that the dielectric property of the substrate is modified by manganese atoms and indicating that electronic correlations in grpahene can also be tuned by foreign atoms. These results pave the way for promising device application using graphene that is semiconducting and charge neutral.