Changyoung 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

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 for various

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

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 RuO₂ is a prototypical candidate for realizing the prospects of altermagnetism. However, the experimental studies on RuO₂ are still in the early stages. In this study, the magnetic responses in RuO₂ film are investigated b

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

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 Gd₃ SnC antiperovskite is re

Bare and Sb covered GaAs(110) surfaces were studied with a photoelectron microscope. For the cleaved surfaces, maximum band bendings of 0.85 and 0.50 eV was observed for n- and p-type GaAs, respectively. For n-type, evaporation of Sb reduces the band bending from 0.85 to 0.55 eV. Annealing p-GaAs at 350 °C almost restored the flatband condition for an initially unpinned area. A reduction of band bending was observed for an initially heavily pinned area. This suggests that the cleavage defects or

The design and testing of an imaging band-pass analyzer (BPA) consisting of two 90° spherical sectors operating in a magnetic-field-free region is described. Image electrons injected nearly parallel to one another and perpendicular to the first 90° sector are focused into an energy plane where electrons of desired energy are band-pass filtered. A second 90° sector is used to recover the energy-filtered image. With a 1-mm aperture, energy resolution of 1% and spatial resolution of 0.01% of the ma

Copper-based high-temperature superconductors share a common feature in their crystal structure, which is the presence of a CuO₂ plane, where superconductivity takes place. Therefore, important questions arise as to whether superconductivity can exist in a single layer of the CuO₂ plane and, if so, how such superconductivity in a single CuO₂ plane differs from that in a bulk cuprate system. To answer these questions, studies of the superconductivity in cuprate mo

A prototype of the 250-μm pitch 8 × 8 silicon photomultiplier (SiPM) array was designed and fabricated by the 0.2 μm 5-metal Silicon on Insulator (SOI)-CMOS technology aiming at the monolithic integration of sensors and front-end electronics. The SOI technology enables the 3D integration of electronics without a mechanical bonding that allows the pixel size refinement, the backside illumination, and the improved electronics performance. The signal of SiPM is processed by the front-end electronic