Soshi Iimura

Iron arsenide superconductors based on the material LaFeAsO(1-x)F(x) are characterized by a two-dimensional Fermi surface (FS) consisting of hole and electron pockets yielding structural and antiferromagnetic transitions at x=0. Electron doping by substituting O(2-) with F(-) suppresses these transitions and gives rise to superconductivity with a maximum T(c) of 26 K at x=0.1. However, the over-doped region cannot be accessed due to the poor solubility of F(-) above x=0.2. Here we overcome this

The hydride ion (H^-) is a unique anionic species that exhibits high reactivity and chemical energy. H^- conductors are key materials to utilize advantages of H^- for applications, such as chemical reactors and energy storage systems. However, low H^- conductivity at room temperature (RT) in current H^- conductors limit their applications. In this study, we report a H^- conductivity of ∼1 mS cm^-1 at RT, which is higher by 3 o

In iron-based superconductors, high critical temperature (<i>T</i>_c) superconductivity over 50 K has only been accomplished in electron-doped <i>hRE</i>FeAsO (<i>hRE</i> is heavy rare earth (<i>RE</i>) element). Although <i>hRE</i>FeAsO has the highest bulk <i>T</i>_c (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a sy

We investigate the doping dependence of the magnetic excitations in the two-superconducting-dome system LaFeAsO${}_{1\ensuremath{-}x}$D${}_{x}$. Using inelastic neutron scattering, spin fluctuations at different wave numbers were observed under both superconducting domes around $x$ $=$ 0.1 and 0.4 but vanished at $x$ $=$ 0.2 corresponding to the ${T}_{\mathrm{c}}$ valley. Theoretical calculations indicate that the characteristic doping dependence of the spin fluctuations is rationally explained

We perform transport measurements and band structure calculations of electron-doped $\mathrm{LaFeAs}{\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{H}}_{x}$ over a wide range of $x$ from 0.01 to 0.66. The ${T}^{2}$ and $\ensuremath{\surd}T$ dependency of the resistivity are observed at $x\ensuremath{\sim}0.17$ and 0.41, respectively. The sign change of ${R}_{\mathrm{H}}$ without opening of the spin-density-wave gap for $0.45\ensuremath{\le}x\ensuremath{\le}0.58$ and $T&lt;{T}_{\mathrm{N}}$ as well as th

Copper iodide (CuI) is a promising p-type transparent semiconductor with excellent carrier mobility. However, the high hole concentration in conventionally fabricated CuI including the single crystal hinders its applicability to the channel layer of thin-film transistors. We found that Zn substitution into Cu⁺ sites can effectively reduce the hole concentration. Experimental and computational examinations showed that the dominant mechanism involved the formation of a defect pair, the

Iron-based superconductors have grown to be a new continent of high Tc superconductors comparable to cuprates. The optimal critical temperature (Tc) of 56 K in electron-doped 1111-type iron oxypnictides attracts considerable attention of physicists and chemists. Carrier doping is not only essential to induce superconductivity but also is a critical parameter that governs the electronic, magnetic, and crystallographic properties of ground states in high-Tc superconductors. Hydride ion (H-) which

Anion-excess fluorite is a unique structure type of inorganic crystals and is well known as an appropriate crystal structure for fast anion conduction. In particular, the introduction of excess anion and charged defect by chemical doping significantly enhances the conductivity. However, the clustering of dopants and defects is the main obstacle for further enhancement of conductivity. We investigated the pressure–chemical composition phase diagram of the LaHO–LaH3 system, in which the highly H–

Resistive switching induced by ion migration is promising for applications such as random-access memory (ReRAM) and neuromorphic transistors. Hydride ions (H^-) are an interesting candidate as the migration ion for resistive switching devices because they have fast diffusion in several compounds at room temperature and doping/dedoping can be used effectively to achieve significant changes in the electronic conductivity. Here, we report reversible resistive switching characteristics in

New manganese arsenides CsMn₄As₃, RbMn₄As₃, and KMn₄As₃ were synthesized by solid-state reaction. They consist of edge-sharing MnAs₄ tetrahedra, which are a building block similar to those of Fe-based superconductors. CsMn₄As₃ and RbMn₄As₃ adopt the KCu₄S₃-type structure (tetragonal P4/ mmm space group, No. 123) with a Mn₄As₃ double

Hydride ions (H^-) in solvents are chemically active anions with strong electron-donating ability and are used as reducing agents in organic chemistry. Here, we evaluate the energy level of 1s-electrons in H^- accommodated in solid lanthanum hydrides, LaH_<i>x</i> (2 ≤ <i>x</i> ≤ 3), by photoemission (ultraviolet photoelectron and photoelectron yield spectroscopies) measurements and density functional theory calculations. We show that a very shallow valance band max