50% of the Nobel Prize in Physics 2020 was awarded to the discovery of the supermassive compact object (candidate of massive black hole) at the center of our galaxy, which was pioneered by American and European groups in the latter half of the 1990s. This article explains its impact on the test of General Relativity at a strong gravity regime. Concerning the General Relativity test, not only the American and European groups but also our Japanese group have been making contributions, using the world largest infra-red telescopes. Our research is also introduced.

Conformational change of biomolecules is essential to understand the fundamental properties of biology such as enzymatic properties, and its molecular detail should be addressed. Molecular dynamics simulations are an indispensable tool to investigate this problem, but conformational change is a “rare event” in a molecular sense because it accompanies activation processes, and conventional MD simulations are not feasible. To attack this problem, we introduce some of path sampling methods including Onsager-Machlup action method, string method, and weighted ensemble method, and illustrate some molecular examples.

We compared positron and electron-stimulated desorption (e⁺SD and ESD) of positive ions from a TiO₂(110) surface. Although desorption of O⁺ ions was observed in both experiments, the yield of e⁺SD was one order of magnitude higher than the yield of ESD at an incident energy of 500 eV. Furthermore, e⁺SD of O⁺ ions caused even below the ESD threshold and remained highly efficient with incident positron energies between 10 eV and 600 eV. The results indicate that e⁺SD of O⁺ ions is predominantly caused by pair annihilation of surface-trapped positrons with inner-shell electrons. We also observed the ion desorption from water chemisorbed on the TiO₂ surface and found that the desorption of specific ions was enhanced in e⁺SD. This finding corroborates our conclusion that annihilation-site selectivity of positrons results in site-selective ion desorption.

Recently, the coupling of Dirac/Weyl fermions with quantum phenomena in solids, such as magnetism, has been intensively investigated, since unconventional transport and optical phenomena were revealed. However, the material variety of the correlated topological materials has been still limited. Here we propose that layered material AMn X₂( A: alkaline and rare earth ions, X: Sb, Bi) is a promising platform for this. AMn X₂ consists of the alternative stack of the X ^－square net layer hosting quasi 2D Dirac fermions and the A²⁺–Mn²⁺–X ^3－magnetic block layer. By systematically substituting the A and X sites, we have demonstrated that the Dirac fermion state in the former layer can be controlled and even enriched by the coupling with the physical properties of the block layer.