Chang-Young Kim

Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt–Sn/Pt(111) 2 × 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear

In spectroscopic experiments, data acquisition in multi-dimensional phase space may require long acquisition time, owing to the large phase space volume to be covered. In such a case, the limited time available for data acquisition can be a serious constraint for experiments in which multidimensional spectral data are acquired. Here, taking angle-resolved photoemission spectroscopy (ARPES) as an example, we demonstrate a denoising method that utilizes deep learning as an intelligent way to overc

Abstract Direct band-gap semiconductors play the central role in optoelectronics. In this regard, monolayer (ML) MX 2 (M = Mo, W; X = S, Se) has drawn increasing attention due to its novel optoelectronic properties stemming from the direct band-gap and valley degeneracy. Unfortunately, the more practically usable bulk and multilayer MX 2 have indirect-gaps. It is thus highly desired to turn bulk and multilayer MX 2 into direct band-gap semiconductors by controlling external parameters. Here, we

Abstract The metal–insulator transition (MIT) in correlated materials is a novel phenomenon that accompanies a large change in resistivity, often many orders of magnitude. It is important in its own right but its switching behavior in resistivity can be useful for device applications. From the material physics point of view, the starting point of the research on the MIT should be to understand the microscopic mechanism. Here, an overview of recent efforts to unravel the microscopic mechanisms fo

Abstract The recent prediction of the new magnetic class, altermagnetism, has drawn considerable interest, fueled by its potential to host novel phenomena and to be utilized in next‐generation spintronics devices. Among many promising candidates, rutile RuO 2 is a prototypical candidate for realizing the prospects of altermagnetism. However, the experimental studies on RuO 2 are still in the early stages. In this study, the magnetic responses in RuO 2 film are investigated by the Planar Hall eff

A photoelectron microscope operating with a retarding field analyzer can exploit core level energy shifts in order to image Fermi-level variations of semiconductor surfaces. Fermi-level maps of cleaved n- and p-type GaAs (110) resolved to better than 10 μm indicate lateral variations in the surface Fermi level which are often quite abrupt. In agreement with earlier, lower resolution work [J. M. Palau, E. Testemale, and L. Lassabatere, J. Vac. Sci. Technol. 19, 192 (1981)],1 Fermi-level topograph

In condensed matter physics, the Kagome lattice and its inherent flat bands have attracted considerable attention for their prediction and observation to host a variety of exotic physical phenomena. Despite extensive efforts to fabricate thin films of Kagome materials aimed at modulating flat bands through electrostatic gating or strain manipulation, progress has been limited. Here, we report the observation of a d-orbital hybridized Kagome-derived flat band in Ag/Si(111) 3 × 3 as revealed by an

Abstract The heavy fermion state with Kondo-hybridisation (KH), usually manifested in f -electron systems with lanthanide or actinide elements, was recently discovered in several 3 d transition metal compounds without f -electrons. However, KH has not yet been observed in 4 d /5 d transition metal compounds, since more extended 4 d /5 d orbitals do not usually form flat bands that supply localised electrons appropriate for Kondo pairing. Here, we report a substitution- and temperature-dependent

Abstract Each plane of layered ReS 2 and ReSe 2 materials has 1D chain structure, from which intriguing properties such as 1D character of the exciton states and linearly polarized photoluminescence originate. However, systematic studies on the 1D character of charge carriers have not been done yet. Here, we report on systematic and comparative studies on the energy-momentum dispersion relationships of layered transition metal dichalcogenides ReS 2 and ReSe 2 by angle resolved photoemission. We

Abstract Hund’s rule coupling ( J ) has attracted much attention recently for its role in the description of the novel quantum phases of multi-orbital materials. Depending on the orbital occupancy, J can lead to various intriguing phases. However, experimental confirmation of the orbital occupancy dependency has been difficult as controlling the orbital degrees of freedom normally accompanies chemical inhomogeneities. Here, we demonstrate a method to investigate the role of orbital occupancy in

Abstract Inverted structures of common crystal lattices, referred to as antistructures, are rare in nature due to their thermodynamic constraints imposed by the switched cation and anion positions in reference to the original structure. However, a stable antistructure formed with mixed bonding characters of constituent elements in unusual valence states can provide unexpected material properties. Here, a heavy‐fermion behavior of ferromagnetic gadolinium lattice in Gd 3 SnC antiperovskite is rep

Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic-scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of co