The importance of characterizing electronic properties of μm- and nm-scale world cannot be overemphasized. Understanding based on the atomic level characterization methods is becoming increasingly important in elucidating new quantum phenomena and developing functional materials and devices. In photoelectron spectroscopy (PES), the photoelectrons emitted from the sample surface irradiated with X-rays are measured to clarify the composition and electronic structure of the sample. So far, high-resolution electron analyzers have been developed to measure the valence band dispersion of crystalline samples, but they average information over a wide field of view. However, the most interesting materials and useful devices are often micrometer-scale polycrystalline or highly integrated structures. Therefore, a high-specification electron energy and momentum analysis apparatus that also has microscope functions was desired. The momentum microscope, a combination of projection-type electron analyzer and photoelectron microscope, simultaneously realizes a microscope function for magnifying and observing minute parts of complicated-structured samples with element selectivity and a spectroscopy function for visualizing electron behavior (momentum) that determines the electronic properties of a sample. Now we have introduced the latest momentum microscope at the undulator-based soft X-ray beamline of UVSOR providing the optimal energy light for valence bands and core levels of various elements. Microscopy with a spatial resolution of 50 nm and photoelectron spectroscopy (field of view: 2 μm) with energy / momentum resolutions of 20 meV / 0.01 Å-1 at 9 K (-264 ºC) are successfully demonstrated. In addition to the features of momentum microscope, the sample temperature can be freely changed up to 400 K (127 ºC), which enables in-situ observation of phase transition in the materials. One can investigate how the composition, structure, and electronic state of materials are related to electronic properties and functions. A method to directly observe the electronic structure of μm-sized materials are realized.　The momentum microscope opens the door to direct observation of the Fermi surface and band structure of μm-sized targets such as surface atomic sites, thin films and interfaces, molecular adsorbates, and polycrystals, which was difficult with conventional electron energy analyzers. It enables electronic property and function analysis from a new point of view, such as direct observation of structure and electronic state changes where superconductivity and catalytic activity are occurring. In addition to contributing to basic science and applied research, we aim to make this new pioneering analyzer and analysis method a precursor to measurement technology innovation.

物質中では電子は原子に散乱され、互いに干渉しあいながら、波のように運動しています。光を照射し、電子を真空中に取り出して計測する光電子分光法は、こうした物質中の電子の素性を原子レベルで解明する有力な手法として発展してきました。面白いことに、電子は波の性質を保持したまま光電子として真空中に飛び出すため、光電子の角度分布には、物質中での電子の運動や原子の並び方に由来する実に美しい波紋文様（光電子ホログラム）が現れます。光電子が織りなす「アート」を物理法則に基づいて解析すると、時として原子の世界と実用的な技術が結び付く発見に至る、それが私たちの研究の醍醐味です。 私たちは分子研極端紫外光研究施設（UVSOR）に世界最先端の光電子運動量顕微鏡の実験拠点を新設しました。光電子運動量顕微鏡は、光電子ホログラムを可視化する新しい発想の分析器で、物性が発現している微小領域に照準を合わせ、実際にその物性を司る電子状態にズームインすることができます。私たちが特に注目する電子スピンは特異な磁気特性・電気伝導・光熱励起・化学反応など様々な量子現象の源泉です。そこで、私たちは独自の3Dスピンベクトルイメージング装置や元素選択的な共鳴光電子回折分光法を創案しました。これらを光電子運動量顕微鏡と融合し、電子物性・機能が発現する現場を直接分析する研究を進めています。独自の分析装置・分光手法を駆使して電子の運動を精緻・包括的に解析し、まだ誰も知らない新奇現象を捕まえ、電子・スピン物性科学の新展開を目指します。