Shunsuke Kitou

We investigated the precise crystal structures and electronic states of a quasi-two-dimensional molecular conductor $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{I}}_{3}$ at ambient pressure. The electronic resistivity of this molecular solid shows metal-to-insulator (MI) crossover behavior at ${T}_{\mathrm{MI}}=50\phantom{\rule{4pt}{0ex}}\mathrm{K}$. Our x-ray diffraction and $^{13}\mathrm{C}$ nuclear magnetic resonance experiments revealed that $\ensuremath{\alpha}\tex

A quasi-one-dimensional organic charge-transfer salt (TMTTF)_{2}PF_{6} undergoes a multistep phase transition as the temperature decreases. One of these transitions is called a "structureless transition," and these detailed structures were unknown for many years. With synchrotron x-ray diffraction, we observed a slight structural difference owing to the effect of charge-order transition between two TMTTF molecules in a dimer, which corresponds to the charge transfer δ_{CO}=0.20e. The two-dimensi

$1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$ has a semimetallic band structure at room temperature and undergoes phase transition to a triple-$q$ charge-density wave (CDW) state with a commensurate superlattice structure $(2a\ifmmode\times\else\texttimes\fi{}2a\ifmmode\times\else\texttimes\fi{}2c)$ below ${T}_{c}\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at ambient pressure. This phase transition is caused by cooperative phenomena involving electron-phonon and electron-hole

The orbital degree of freedom of electrons greatly influences the physical properties of materials such as magnetic order and unconventional superconductivity. An orbital is a minimal unit of "shape," and the orbital state can be unraveled by observing the spatial anisotropic distribution of electrons. However, it is difficult to experimentally extract the orbital information in a crystal because of various technical problems. Here, the Ti-3d orbital state in perovskite-type oxides RTiO 3 (R = Y

The physical properties of molecular crystals are governed by the frontier orbitals of molecules. A molecular orbital, which is formed by superposing the atomic orbitals of constituent elements, has complicated degrees of freedom in the crystal because of the influence of electron correlation and crystal field. Therefore, in general, it is difficult to experimentally observe the whole picture of a frontier orbital. Here, we introduce a new method called “core differential Fourier synthesis” (CDF

An anomalously high valence state sometimes shows up in transition-metal oxide compounds. In such systems, holes tend to occupy mainly the ligand p orbitals, giving rise to interesting physical properties such as superconductivity in cuprates and rich magnetic phases in ferrates. However, no one has ever observed the distribution of ligand holes in real space. Here, a successful observation of the spatial distribution of valence electrons in cubic perovskite SrFeO₃ by high-energy X-ra

The phase transition phenomenon in a semimetallic $1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$ has attracted attention as an excitonic insulator. However, as the phase transition accompanying superlattice peaks has the $q$ vector connecting the Fermi surfaces of the three-dimensional shape of hole and electron pockets, it also assumes the charge density wave (CDW) state owing to the electron--phonon interaction. To understand the electronic state at the low temperature, control of the chemical

Transition-metal atoms with d electrons sometimes form clusters in crystals, which significantly affect the physical properties. Such a cluster formation frequently accompanies a change in the crystal system, leading to the presence of domains with different crystal orientations. In particular, the cubic symmetry is rarely retained after the cluster formation. Here, we identify a cubic-to-cubic phase transition in lacunar spinel GaNb4Se8, where the change in the lattice parameter is less than 0.

$\mathrm{C}{\mathrm{u}}^{+}$ ion behavior is one of the heavily discussed topics in physical and material fields because of its unclear behavior and high potential in materials application. To provide a breakthrough in this field, comprehensive research that connects the real space and the reciprocal lattice (momentum) space is effective. Here, we investigated the $\mathrm{C}{\mathrm{u}}^{+}$ ion behavior in two-dimensional layered system $\mathrm{C}{\mathrm{u}}_{0.33}\mathrm{TiS}{\mathrm{e}}_{2

Structural parameters in quasi-one-dimensional organic conductors ${(\mathrm{TMTTF})}_{2}X$ ($X=\mathrm{Nb}{\mathrm{F}}_{6}, \mathrm{As}{\mathrm{F}}_{6}, \mathrm{P}{\mathrm{F}}_{6}$, and Br) are investigated by synchrotron x-ray diffraction. The temperature dependences of the crystal structures differ significantly between octahedral and monatomic anion systems, corresponding to the presence or absence of a charge-ordering transition. Changes in temperature and chemical pressure control the dime

The metal-insulator transition (MIT) in vanadium dioxide $({\mathrm{VO}}_{2})$ due to V-V dimerization has been extensively discussed for decades. While it is widely acknowledged that electron correlations, Peierls instabilities, and molecular orbital formations are crucial for understanding the MIT of ${\mathrm{VO}}_{2}$, the primary origin of the MIT remains controversial. In this study, we delve into the crystal structure and orbital state of ${\mathrm{VO}}_{2}$ through synchrotron x-ray diff

A real-space observation of the distribution state of valence electrons, which is responsible for physical properties, is a key methodology to understand the relation between the structure and functions of matter. Here, we observe Mo $4d$ orbital electrons at subangstrom resolution in a pyrochlore-type oxide ${\mathrm{Nd}}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ based on the core differential Fourier synthesis (CDFS) analysis of high-energy x-ray diffraction data. The ${\mathrm{Mo}}^{4+} 4{d}^{2}$

The metal-insulator transition (MIT) in vanadium dioxide VO$_2$ due to V-V dimerization has been extensively discussed for decades. While it is widely acknowledged that electron correlations, Peierls instabilities, and molecular orbital formations are crucial for understanding the MIT of VO$_2$, the primary origin of the MIT remains controversial. In this study, we delve into the crystal structure and orbital state of VO$_2$ through synchrotron x-ray diffraction experiments. The molecular orbita

An anomalously high valence state sometimes shows up in transition-metal oxide compounds. In such systems, holes tend to occupy mainly the ligand $p$ orbitals, giving rise to interesting physical properties such as superconductivity in cuprates and rich magnetic phases in ferrates. However, no one has ever observed the distribution of ligand holes in real space. Here, we report a successful observation of the spatial distribution of valence electrons in cubic perovskite SrFeO$_3$ by high-energy