Yuka Ikemoto

Imaging Phase Separation near the Mott Boundary of the Correlated Organic Superconductors κ-(BEDT-TTF)2X

Electronic phase separation consisting of the metallic and insulating domains with 50-100 microm in diameter is found in the organic Mott system kappa-[(h8-BEDT-TTF)(1-x)(d8-BEDT-TTF)x]2Cu[N(CN)2]Br by means of scanning microregion infrared spectroscopy using the synchrotron radiation. The phase separation appears below the critical end temperature 35-40 K of the first-order Mott transition. The observation of the macroscopic size of the domains indicates a different class of the intrinsic electronic inhomogeneity from the nanoscale one reported in the inorganic Mott systems such as high-Tc copper and manganese oxides.

Optical studies of nanoscale materials incorporated in the space of zeolite crystals

Abstract Optical spectroscopy is used for the characterization of the quantum electronic state of nanoscale materials incorporated in zeolite crystals. Alkali metal clusters generated in zeolite exhibit interesting phenomena in optical properties as well as magnetic ones. Potassium clusters incorporated in zeolite LTA have shown ferromagnetism at low temperatures. The origin of the ferromagnetism was explained by the itinerant electron model. The infrared spectrum and magnetization curves, however, suggest that the itinerant electron model is not applicable to the ferromagnetism. Magnetic properties are interpreted based on the model of ferrimagnetism. Polarized micro-optical spectroscopy suggests the possibility of the one-dimensional array of potassium clusters in zeolite MOR single crystal

Optical Probe of Carrier Doping by X-Ray Irradiation in the Organic Dimer Mott Insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl

We investigated the infrared optical spectra of an organic dimer Mott insulator kappa-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl, which was irradiated with x rays. We observed that the irradiation caused a large spectral weight transfer from the midinfrared region, where interband transitions in the dimer and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this caused the Mott gap to collapse. The increase of the Drude part indicates a carrier doping into the Mott insulator due to irradiation defects. The strong redistribution of the spectral weight demonstrates that the organic Mott insulator is very close to the phase border of the bandwidth-controlled Mott-insulator-metal transition.

Real Space Imaging of the Metal–Insulator Phase Separation in the Band Width Controlled Organic Mott System κ-(BEDT-TTF)2Cu[N(CN)2]Br

Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal–insulator fraction with the substitution ratio x in κ-[( h -BEDT-TTF) 1- x ( d -BEDT-TTF) x ] 2 Cu[N(CN) 2 ]Br, of which band width is controlled by the substitution ratio x between the hydrogenated BEDT-TTF molecule ( h -BEDT-TTF) and the deuterated one ( d -BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.

Loading density dependence of ferromagnetic properties in potassium clusters arrayed in a simple cubic structure in zeolite LTA

Magnetic properties are investigated for potassium clusters arrayed in zeolite LTA. The potassium loading density per cluster, n, is changed up to 7.2 per cluster. The n-dependence of the Curie constant and the magnetization are measured in detail. Possible origins of ferromagnetic properties are discussed. ( 2000 Elsevier Science B.V. All rights reserved.

Synchrotron FTIR micro-spectroscopy for structural analysis of Lewy bodies in the brain of Parkinson’s disease patients

Lewy bodies (LBs), which mainly consist of α-synuclein (α-syn), are neuropathological hallmarks of patients with Parkinson’s disease (PD). The fine structure of LBs is unknown, and LBs cannot be made artificially. Nevertheless, many studies have described fibrillisation using recombinant α-syn purified from E. coli. An extremely fundamental problem is whether the structure of LBs is the same as that of recombinant amyloid fibrils. Thus, we used synchrotron Fourier transform infrared micro-spectroscopy (FTIRM) to analyse the fine structure of LBs in the brain of PD patients. Our results showed a shift in the infrared spectrum that indicates abundance of a β-sheet-rich structure in LBs. Also, 2D infrared mapping of LBs revealed that the content of the β-sheet structure is higher in the halo than in the core, and the core contains a large amount of proteins and lipids.

Photogenerated Carriers in SrTiO3 Probed by Mid-Infrared Absorption

Infrared absorption spectra of SrTiO 3 have been measured under above-band-gap photoexcitations to study the properties of photogenerated carriers, which should play important roles in previously reported photoinduced phenomena in SrTiO 3 . A broad absorption band appears over the entire mid-infrared region under photoexcitation, which is attributed to absorption by the photogenerated carriers occupying in-gap states. The photoinduced absorption is strongly dependent on temperature even below 35 K, where the average photocarrier density is nearly constant. The data show that the density of in-gap states occupied by the photocarriers is high and distributed over a wide energy range extending to the band edges.

Far-infrared spectroscopy of electronic states of CuIr2Se4 at high pressure

The spinel compound CuIr 2 Se 4 at atmospheric pressure is a metal of wide temperature range, but undergoes a stabilization of the insulating phase from the metal phase at high pressures above 3 GPa. To study the change in electronic state at pressure, we performed a spectromicroscopic measurement in the far-infrared to visible region on polycrystalline CuIr 2 Se 4 at high pressures up to 8 GPa at room temperature. The peak structure at around 0.2 eV in the optical conductivity spectra at atmospheric pressure, whose origin was assigned to the hybridized band, was found to lose its intensity at pressure accompanied by the rapid suppression of the Drude component. This change in the optical spectra at pressure indicates that the pseudo-gap state formed in the vicinity of the Fermi level is very sensitive to pressure. We discuss this behaviour in relation to the instability of the metallic state due to the increase in the degree of hybridization with pressure.

Soft x-ray spectroscopy of Ba24Ge100: Electronic phase transition and Ba-atom rattling

The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.

Infrared study of spin crossover Fe-picolylamine complex

Infrared (IR) absorption spectroscopy has been used to probe the evolution of microscopic vibrational states upon the temperature- and photo-induced spin crossovers in [Fe(2-picolylamine) 3 ]Cl 2 EtOH (Fe–pic). To overcome the small sizes and the strong IR absorption of the single crystal samples used, an IR synchrotron radiation source and an IR microscope have been used. The obtained IR spectra of Fe–pic show large changes between high-spin and low-spin states, for both the temperature- and the photo-induced spin crossovers. In contrast, the spectra in the temperature- and photo-induced high-spin states are relatively similar to each other, however they show distinct differences below 750 cm -1 . This demonstrates that the photo-induced high-spin state involves microscopically different characters from those of the temperature-induced high-spin state. The results are discussed in terms of local pressure and structural deformations within the picolylamine ligands, and in terms of their possible relevance...