Surface Science with condensed-matter physics
Even though surface science is an old-fashioned research area, it has an essential role in condensed matter physics and device applications. As the thickness of the devices is going thinner, it is hard to neglect the influence of surface and interfaces. Moreover, surface/interface physics has been raised again since the observation of the topological matter. Our goal is to understand Low D systems with surface/interface properties.
Physical Review Letters 110, 036801(2013), New Journal of Physics 16, 093030 (2014), ACS Nano 9 (11),10621–10627 (2015), Applied Surface Science 504, 144341 (2020)
Low-dimensional (low-D) electronic systems
Since the rise of graphene and topological insulators, vdW crystals have been the key to novel device applications. For example, Dirac fermions in graphene show a chiral structure ordered by pseudospins, whereas topological insulators show the chiral spin structure of surface states. And this chiral structure is the essential physics underneath the non-trivial electronic properties of matter. Our insight is to probe such chiral electron bands and to find a connection with the physical properties of vdW crystals.
Physical Review Letters 116, 186802 (2016), Journal of Electron Spectroscopy and Related Phenomena 216, 86-91 (2016), Nano Letters 17(3), 1610-1615 (2017), Physical Review B 101, 235431 (2020)
Angle-resolved Photoemission Spectroscopy (ARPES)
ARPES is a powerful tool for exploring the electronic states of matter in reciprocal space. We can measure the photoelectron currents, converting these electrons from the escape angle and kinetic energy to the momentum and binding energy. The spectral function can be analyzed in terms of dispersion, many-body interaction, and the matrix element effect (probability of photoexcitation) might be understood by the electron bands, orbital, spin, and pseudospin nature.
Quasiparticles measured by ARPES
There are numerous exotic features in quantum materials, such as bandgap, non-trivial topological states, and electron-boson coupling. We are interested in these quasi-particles, and our goal is to understand the electrical properties of quantum materials with their electronic states.
Physical Review Letters 119, 226801 (2017), Nature Materials 17, 676–680 (2018), Nature Materials 19, 277–281(2020), Scientific Reports 10, 12957 (2020) etc...
Spatially-resolved ARPES (Nano ARPES, Nano ESCA)
The ARPES community has tried to explore the electronic structure in a tiny region of the crystallised surface. From this manner, several beamlines in the world developed a sub-micron-sized beam by employing optics with high-numerical-aperture. Moreover, some technicians developed the PEEM system, which is called Nano ESCA. We have challenges for the potential science cases of such spatially-resolved ARPES technics.
Applied Surface Science 532, 147390 (2020), Nature Communications 12, 2874 (2021), New Journal of Physics (2022, accepted)
Photoelectron Spectroscopy
ARPES(ARUPS), Spin-resolved ARPES(SR ARPES) and Spatially-resolved ARPES (Nano ARPES)
XPS, Nano ESCA, PEEM
Electron Diffraction: LEED and RHEED
Computation Technics: Tight-binding Model, DFT Packages (QUESTAAL and WEIN2K)