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The silicon clathrates--materials composed of metal-doped Si(20) dodecahedra--were identified as the first superconductors based on pure silicon networks. The mechanism of superconductivity in these materials can be obtained by studying their phonon modes, as modified by isotope substitution, and specific-heat measurements. Here, we present experimental studies that provide strong evidence that superconductivity in Ba(8)Si(46) is explained in the framework of phonon-mediated Bardeen-Cooper-Schriefer theory. Analyses using the McMillan approximation of the Eliashberg equation indicate that the superconducting mechanism is in the medium coupling regime, but at the high-end limit. The large density of states at the Fermi level, which arises from hybridization of the Si(20) cluster and Ba orbitals, is responsible for the unexpectedly high superconducting temperature. The temperature evolution of the specific heat unambiguously shows that this is an s-wave symmetry superconductor.

We have completed a systematic study of the magnetization of a single crystal of double perovskite Sr 2 FeMoO 6 over a wide range of temperatures and fields. Near the ordering temperature of 405.0 K, the magnetization is described by critical exponents β =0.50±0.03 and γ =1.20±0.03. At low temperature, the compound is ferromagnetic, but the moment corresponds to only 3.3 μ B /formula unit, significantly less than the 3.6 expected. We discuss these observations in terms of mis-site defects of the Fe and Mo ions.

Using original modulation technique, the longitudinal electron spin-lattice relaxation time T 1 has been measured in a series of nearly cubic La 1− x Ca x MnO 3 ( x =0.1; 0.2; 0.25; 0.33) and layered La 2−2 x Sr 1+2 x Mn 2 O 7 ( x =0.4 and 0.5) manganites both in paramagnetic state and around the temperature ( T c ) of the magnetic ordering. The data are compared with the evolution of the transverse relaxation time T 2 as determined from the ESR linewidth. Well above T c , the T 1 = T 2 equality is confirmed, whereas a pronounced slowing down of T 1 is observed in all the materials as T c is approached. The temperature dependence of T 1 is found to be consistent with that of Tχ ( T ), where χ ( T ) represents the temperature dependence of the electron-spin susceptibility determined from the ESR absorption area. The interpretation suggests freezing the local field fluctuations due to polarization of superparamagnetic clusters in the external magnetic field.

Bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaics (OPV). In order to improve the incident photon-to-current efficiency (IPCE) of the BHJ solar cell, a comprehensive understanding of the ultrafast dynamics of excited species, such as singlet exciton (D*), interfacial charge-transfer (CT) state, and carrier (D+), is indispensable. Here, we performed femtosecond time-resolved spectroscopy of two prototypical BHJ blend films: poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend film and poly(9,9′-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) blend film. We decomposed differential absorption spectra into fast, slow, and constant components via two-exponential fitting at respective probe photon energies. The decomposition procedure clearly distinguished photoinduced absorptions (PIAs) due to D*, CT, and D+. Based on these assignments, we will compare the charge dynamics between the F8T2/PC70BM and P3HT/PCBM blend films.

We present a systematical study of thermal Hall effect on a bismuth single crystal by measuring resistivity, Hall coefficient, and thermal conductivity under magnetic field, which shows a large thermal Hall coefficient comparable to the largest one in a semiconductor HgSe. We discuss that this is mainly due to a large mobility and a low thermal conductivity comparing theoretical calculations, which will give a route for controlling heat current in electronic devices., Comment: 4pages, 3 figures

Giant magnetotransport phenomena including the field-induced nonmetal-metal transition have been found in single crystals of La 1- x Sr x MnO 3 near the critical composition ( x ≈0.17) for the nonmetal-metal transition and in the temperature region around the magnetic phase transition. Change of the resistivity shows a universal curve as a function of the magnitude of temperature- or field-induced magnetization, the most of which agrees with the prediction by the D =∞ and S =∞ Kondo lattice model with strong ferromagnetic (Hund) coupling.

Effects of hydrostatic pressure on Raman scattering and electronic absorption spectra have been investigated in layered cupric chloride (C2H5NH3)2CuCl4, consisting of strongly Jahn–Teller (JT) deformed CuCl4 layers. We observed selective deactivation of the Cu–Cl stretching modes at a pressure above ∼4 GPa, and interpreted the phenomena in terms of disappearance of the in‐plane lattice distortion of the CuCl4 layer. The pressure‐induced structural change reduces the charge‐transfer (CT)‐type gap from the ligand (Cl3p) to metal (Cu3dx2−y2) sites by ∼0.4 eV, and perhaps produces the two‐dimensional electronic states analogous to that of the parent compounds for the cupric superconductors.

Effects of hydrostatic pressure on the Raman spectra have been investigated for four kinds of 1,3‐diketone crystals with hydrogen‐bonded molecular chains. In all the crystals we studied, intense CO stretching Raman mode shows pressure‐induced softening reflecting compression of the hydrogen bonds. Furthermore, application of pressure broadens the both C=O and C–O stretching modes and intensifies several specific vibrational bands. We ascribed these spectral changes to formation or growth of the kink‐type defects of the hydrogen‐bonded sequence.

The effect of B -site substitution on the critical behavior has been investigated in Cr-doped manganites La 0.7 Ca 0.3 Mn 1- x Cr x O 3 ( x =0.00, 0.03 and 0.06) by means of the pump-probe method. We have observed that the Cr-doping suppresses the critical behavior of the relaxation time τ. This suppression has been interpreted in terms of a reduced correlation length of the photoinduced charge-ordering fluctuations due to the B -site impurities.

Oxidization effects on transport properties have been investigated for half-metallic Sr2FeMoO6+δ film. Contents of the excess oxygen (δ) for the heat-treated films were estimated from elongation of the lattice constant c. With the increase of δ, the magnitude of magnetoresistance (-Δρ/ρ0 at 3 T) increases at 100 K from 0.2% at δ=0.09 to1.4% at δ=0.94. We interpret this enhancement in term of the spatial inhomogeneity of δ and resultant tunneling-type magnetoresistance beyond the insulating region with δloc≥0.5.

Effects of chemical substitution on the superconductivity have been investigated in MgB 2 superconductor. Substitution of the Mn 2+ and Co 2+ ions for the Mg 2+ ions significantly suppresses the transition temperature T c at a rate of d T c /d x =-183 and -83 K. respectively. These doping effects are ascribed to the interaction between the local spin S and the constituent electron s of the Cooper pair.

We have grown large single crystals of SrNbO${}_{3.4+d}$ ($d\ensuremath{\sim}0.03$) with $n=5$ in the homologous series Sr${}_{n}$Nb${}_{n}$O${}_{3n+2}$ by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the $b$ axis is $\ensuremath{-}170$ $\ensuremath{\mu}$V/K at 300 K, which is 1 order of magnitude higher than the $\ensuremath{-}15$ $\ensuremath{\mu}$V/K along the $a$ axis and $\ensuremath{-}25$ $\ensuremath{\mu}$V/K along the $c$ axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.

We investigate thermal rectification in a bulk material with a pyramid shape to elucidate shape dependence of the thermal rectification, and find that rectifying coefficient R is 1.35 for this shape, which is smaller than R=1.43 for a rectangular shape. This result is fully duplicated by our numerical calculation based on Fourier's law. We also apply this calculation to a given shape, and show a possible way to increase R depending on the shape., Comment: 4 pages, 4 figures, accepted for publication in Appl. Phys. Lett

In the nominally hole-doped Mott insulator system ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{TiO}}_{3}$, the metal-insulator transition takes place near x=0.4. A thermal hysteretic behavior of the resistivity is observed in the immediate vicinity of the metal-insulator phase boundary. Application of pressure tends to suppress the quasireentrant (metal-insulator-metal) transition and to stabilize the metallic phase. Measurements of the Hall coefficient and the electronic specific heat indicate that the barely metallic phase at about x=0.4 is characterized by an enhancement of carrier mass rather than by a reduction of carrier density.

Dielectric and thermodynamic properties have been investigated in isotopically mixed crystals ${\mathrm{K}}_{3}$${\mathrm{D}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{H}}_{\mathit{x}}$(${\mathrm{SO}}_{4}$${)}_{2}$ with isolated hydrogen bonds interconnecting the dimeric ${\mathrm{SO}}_{4}^{2\mathrm{\ensuremath{-}}}$ units. The critical temperature ${\mathit{T}}_{\mathit{c}}$ for the antiferroelectric phase transition decreases with increasing proton concentration (x) and eventually the phase transition vanishes for x\ensuremath{\ge}${\mathit{x}}_{\mathit{c}}$\ensuremath{\sim}0.66. The x-dependent behavior of ${\mathit{T}}_{\mathit{c}}$, the dielectric constant \ensuremath{\epsilon}(T), and the specific heat jump \ensuremath{\Delta}C at ${\mathit{T}}_{\mathit{c}}$ are described by simple transverse Ising Hamiltonian. This indicates a determinative role of the proton tunneling in the phase transition and related properties.

Pressure dependence of the electronic states in K-TCNQ (potassium-tetracyanoquinodimethane) has been investigated by measurements of polarized reflectance spectra for the gap transitions. With application of pressure, the Peierls distortion appears to be least affected, whereas the charge gap shows a steep reduction against the pressure at a rate of -0.05 eV/GPa. The pressure-induced increase of the one-electron bandwidth is likely responsible for the observed decrease in the charge gap as argued in terms of the Hubbard model.

The temperature dependence of the structural parameters is investigated in ferromagnetic Mo pyrochlore Nd 2 Mo 2 O 7 , by means of high-resolution time-of-flight (TOF) neutron powder diffraction measurement. The Mo–O–Mo bond angle θ abruptly increases and the Mo–O bond length d decreases with the decrease of the temperature across the ferromagnetic transition temperature ( T C = 97 K). This structural variation suggests that itinerant carriers mediate the ferromagnetic coupling between Mo spins via the double-exchange mechanism.

We have investigated antiferromagnetic (AFM) correlations within the MnO 2 layers in a canted AFM La 1.1 Sr 1.9 Mn 2 O 7 by neutron diffraction study. Intense ferromagnetic (FM) diffuse scattering exists even at room temperature, and the FM correlation grows with decreasing temperature.

K1.88Co [Fe(CN)6]0.97·3.8H2O (I) is obtained from aqueous solutions of KCl, CoCl2, and K4[Fe(CN)6].

We have investigated effects of random substitution of proton sites with deuterons on the temperature‐ and pressure‐induced phase transitions in squaric acid crystal, which consists of ferroelectrically ordered molecular sheets of [C4O4]2−(SQ2−) skeletons and intervening protons or deuterons. In the isotopically mixed crystals (H1−xDx )2SQ, the critical temperature Tc for the dielectric phase transition was found to increase linearly with the deuterium concentration x, while the critical pressure Pc increases nonlinearly with x at 300 K. Around the pressure ∼20 kbar above Pc, the constituent SQ2− skeletons in the paraelectric phase show a symmetry change from the asymmetric (C1h ) to centrosymmetric (C4h ) form, which is likely caused by the deformation of the correlated proton (deuteron) potential.

We observed a reversible symmetry switch of a cobalt ferrocyanide framework by the alkaline cation exchange and resultant control of the optical properties at room temperature.

Brilliant pulsed x‐ray synchrotron radiation (SR) is useful for pump‐probe experiment such as time‐resolved x‐ray diffraction, x‐ray absorption fine structure, and x‐ray spectroscopy. For laser pump‐SR x‐ray probe experiments, short pulsed lasers are generally synchronized to the SR master oscillator controlling the voltage for acceleration of electron bunches in an accelerator, and the interval between the laser and the SR pulses is changed around the time scale of target phenomenon. Ideal delay control produces any time delay as keeping the time‐precision and pointing‐stability of optical pulses at a sample position. We constructed the time delay control module using a continuous phase shifter of radio frequency signal and a frequency divider, which can produce the delayed trigger pulses to the laser without degradation of the time precision and the pointing stability. A picoseconds time‐resolved x‐ray diffraction experiment was demonstrated at SPring‐8 storage ring for fast lattice response by femtosecond pulsed laser irradiation, and suggested the possibility of accurate sound velocity measurement. A delay control unit operating with subpicosecond precision has also been designed for femtosecond pump‐probe experiments using a free electron laser at SPring‐8 campus.

We have developed a pump‐probe X‐ray diffraction measurement system for a sample with irreversible reaction at BL40XU in the SPring‐8. The system mainly consists of a time‐resolved measurement system, a sample disk rotation system, and an X‐ray microbeam system. The time‐resolved measurement system gives time resolution of 50 ps in laser‐pump and X‐ray probe method. A sample disk rotation system for repetitive measurements was made to give a virgin sample for every measurement. The number of repetitions for one sample disk was increased by using the X‐ray microbeam technique. To keep the overlap of the X‐ray microbeam and the laser beam on the sample surface during the disk rotation, the sample disk rotation system was constructed by a low‐eccentric spindle motor. By using this system, the pump‐probe X‐ray diffraction measurement was demonstrated for a crystallization process of a DVD material.

We have developed the structure and optical property coincident measurement system equipped with the photo‐absorption system to the Large Debye‐Scherrer Camera at BL44B2 of the SPring‐8. Both photo‐absorption detecting systems, the Si pin‐photo diode for a 532 nm CW laser and the absorption spectrum covered the range of UV‐IR (200∼1400 nm) for a white beam, are adopted. In order to verify the coincident measurement system, the X‐ray powder diffraction and photo‐absorption with the cyanide complex were performed individually and simultaneously under the temperature changes. As a result, the coincident measurement system performed successfully the one‐to‐one corresponding measurement between X‐ray diffraction and photo‐absorption. In addition, the monitoring of the photo‐absorption informed us the property change of the material for the measurement condition and the sample transformation by temperature, laser etc. as well as damage by high‐brilliance synchrotron radiation X‐ray beam.

2-Carboxy-3-hydroxyphenalenone was found to behave as paraelectrics at room temperatur under ambient pressure, exhibiting an antiferroelectric transition at 40K. The paraelectric property is derived from an inversion of a transverse component of its dipole moment based on the rapid tautomerization in the solid state. A C 2V local symmetry of the molecule revealed by a crystallographic analysis was interpreted in terms of a dynamic disorder based on solid state 13 CNMMR (CP/MAS) measurements. The Curie constant determined from a Curie-Weiss plot turned out to be consistent with the above mechanism.

Infrared absorbance (IR) spectra and Raman scattering spectra were measured as a function of pressure for molecular crystals of several 1,3-diketones, which are composed of hydrogen-bonded π -molecular chains. An unconventional proton-related band is commonly observed in the IR spectra around 1800-2000cm−1 in these compounds. We ascribed the observed band to proton vibration localized around kink-(or antikink-) solitons. The intensity of the band rapidly increases with application of hydrostatic pressure, suggesting increase in number of the solitons-like defects of the molecular chains via deformation of the double-well type proton potential.

Optical spectra (ordinary absorption, photoluminescence, electroabsorption, and two-photon absorption spectra) have been investigated for thin films of polysilanes with a variety of backbone conformations such as trans planar, alternating trans-gauche, helical, and disordered forms. The results observed have revealed new features of one-dimensional exciton states characteristic of each conformation of the polymer backbone

One-photon and two-photon absorption and photoluminescence spectra have been investigated for thin films of poly(dihexylgermane) (PDHG) for a comparison with those of its Si-backbone analog, poly(dihexylsilane) (PDHS), with similar trans-planar backbones. The electronic structures of trans-planar PDHG and PDHS have been shown to resemble each other, including the energy positions of the $^{1}$${\mathit{B}}_{1\mathit{u}}$ and $^{1}$${\mathit{A}}_{\mathit{g}}$ exciton transitions, which is not in accord with a prediction by band-structure calculations. A significant difference of the exciton absorption peak in Si and Ge backbones is seen only for the gauchelike disordered conformation.

Effects of pressure and photo-excitation on the mixed-valence (MV) to single-valence (SV) phase transition in Cs 2 Au 2 Br 6 have been investigated by means of high-pressure Raman spectroscopy. Under pressures, we have found both the permanent (at 6.5 GPa) and transient (at 5.5 GPa) photo-induced phase transitions (PIPTs). The two types of PIPTs have been discussed in terms of the pressure-controlled free-energy potential.

Thermal responses of Prussian blue lattice, that is, a rocksalt-type network of metal ions bridged by cyano group, are systematically investigated for ${(\text{Cs},\text{Rb})}_{x}{M}^{\text{II}}{[{\text{Fe}}^{\text{III}}{(\text{CN})}_{6}]}_{y}z{\text{H}}_{2}\text{O}$ ($M=\text{Ni}$, Cu, Zn, and Cd) and ${(\text{Cs},\text{Rb})}_{x}{M}^{\text{III}}{[{\text{Fe}}^{\text{II}}{(\text{CN})}_{6}]}_{y}z{\text{H}}_{2}\text{O}$ ($M=\text{Fe}$ and Co) by means of the synchrotron-radiation x-ray powder diffraction. We found a universal relation between the coefficient ($\ensuremath{\beta}\ensuremath{\equiv}d\text{ }\text{ln}\text{ }a/dT$; $a$ is lattice constant) of the thermal expansion and magnitude of $a$: $\ensuremath{\beta}$ changes the sign from positive to negative with increase in $a$. We ascribed the negative thermal expansion observed in the large-$a$ region to intrinsic rotational instability of the $[\text{Fe}{(\text{CN})}_{6}]$ unit.

Taking advantage of strong electron-lattice interaction characteristic in quasi-one-dimensional systems, the prototypes of new organic molecular solids with one-dimensional ferroelectricity are presented; the ionic charge-transfer (CT) compounds with the donor-acceptor mixed stacks and the hydrogen-bonded (H-bonded) solids with enol-form π-molecular chains. Dynamical properties of the kink-type domain-walls or solitons in these 1D solids are discussed.

Two-photon-absorption spectra have been investigated for solid films of polysilanes with various Si-backbone conformations such as trans planar, alternating trans-gauche, helical, and disordered forms. In all the polysilanes with ordered backbones, the distinct two-photon-absorption peaks were observed at energies 0.8--1.0 eV above the one-photon-absorption peaks. These one-photon and two-photon transitions are interpreted in terms of the ground and excited states of one-dimensional excitons on the Si backbones.

Electronic phase diagram has been derived for the Prussian-Blue-type cyano-bridged transition-metal compound, ${\text{Na}}_{0.84\ensuremath{-}\ensuremath{\delta}}\text{Co}{[\text{Fe}{(\text{CN})}_{6}]}_{0.71}\ensuremath{\cdot}3.8{\text{H}}_{2}\text{O}$ $(0.0\ensuremath{\le}\ensuremath{\delta}\ensuremath{\le}0.61)$, as a function of the hole concentration $\ensuremath{\delta}$ of the $d$-electron system. The mother compound $(\ensuremath{\delta}=0)$ takes the ${\text{Co}}^{2+}$ $({t}_{2g}^{5}{e}_{g}^{2}:S=3/2)$ and ${\text{Fe}}^{2+}$ $({t}_{2g}^{6}:S=0)$ configuration and is paramagnetic down to zero temperature. At room temperature, the holes are selectively introduced on the Fe site. A slight hole doping $(\ensuremath{\delta}=0.13)$ causes the charge-transfer (CT) transition, that is, cooperative electron transfer from the ${\text{Co}}^{2+}$ site to the ${\text{Fe}}^{3+}$ site, with a decrease in temperature below ${T}_{\text{CT}}\ensuremath{\approx}250\text{ }\text{K}$. With a further increase in $\ensuremath{\delta}$, ${T}_{\text{CT}}$ slightly decreases from $\ensuremath{\approx}230\text{ }\text{K}$ at $\ensuremath{\delta}=0.24$ to $\ensuremath{\sim}210\text{ }\text{K}$ at $\ensuremath{\delta}=0.61$. Accordingly, the nature of the transition changes from the second-order type to the first-order type. In all the concentration ranges, the high-temperature (HT) phase is metastable even at low temperature. In this metastable phase, the ${\text{Fe}}^{3+}$ $({t}_{2g}^{5}:S=1/2)$ species mediate the ferromagnetic exchange coupling between the adjacent ${\text{Co}}^{2+}$ spins. The ferromagnetic transition appears at $\ensuremath{\delta}=0.39$, and the transition temperature ${T}_{C}$ increase from 7 K at $\ensuremath{\delta}=0.39$ to 13 K at $\ensuremath{\delta}=0.61$. Based on these experimental data, we will discuss the significant roles of the coupling between the charge, spin, and lattice degrees of freedom in the transition-metal cyanides.

Dynamics of the charge-transfer (CT) pairs has been investigated for the cyano-bridged ${\mathrm{Co}}^{2+}\text{\ensuremath{-}}{\mathrm{Fe}}^{3+}$ particles grown in a hydrophilic cavities of Nafion 117 film. We decomposed the differential absorption spectra into the fast and slow components. We ascribed the fast and slow components to the Frank-Condon state and the CT $({\mathrm{Co}}^{3+}\text{\ensuremath{-}}{\mathrm{Fe}}^{2+})$ pairs with lattice relaxation, respectively. We found that the lifetime ${\ensuremath{\tau}}_{\mathrm{CT}}$ of the pairs at $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ increases with the absorbed photon density $n$ from ${\ensuremath{\tau}}_{\mathrm{CT}}\ensuremath{\approx}2\phantom{\rule{0.3em}{0ex}}\mathrm{ns}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}\ensuremath{\approx}6\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$, reflecting the attractive interaction between the pairs.

An ultra-high-precision clock system for long time delay has been developed for picosecond time-resolved x-ray diffraction measurements using synchrotron radiation (SR) pulses and synchronized femtosecond laser pulses. The time delay control between pump laser pulse and the probe SR pulse was achieved by combining an in-phase quadrature modulator and a synchronous counter. This method allowed us to change the delay time by a nearly infinite amount while maintaining the precision of +/-8.40 ps. Time-resolved diffraction measurements using the delay control system were demonstrated for precise measurement of an acoustic velocity in a single crystal of gallium arsenide.

We have experimentally investigated the charge density distribution and the electrostatic potential for a charge-ordering doped manganite, ${\mathrm{Nd}}_{1∕2}{\mathrm{Sr}}_{1∕2}{\mathrm{MnO}}_{3}$. In the charge-ordered state, we observed a zigzag pattern of the charge density within the (010) plane. Judging from the ${\mathrm{MnO}}_{6}$ distortion, we ascribed the pattern to the bonding electron in the ${p}_{x(y)}\ensuremath{-}{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ hybridized state, not to the so-called ${d}_{3{x}^{2}\ensuremath{-}{r}^{2}}∕{d}_{3{y}^{2}\ensuremath{-}{r}^{2}}$ orbital ordering. We further calculated the electrostatic potential $U(r)$ from the charge density and the atomic positions, which clearly indicates the checkerboard-type charge disproportionation within the (010) plane.

Effects of the hydrostatic pressure on the magnetic and structural properties are investigated in a charge-transfer material, $\mathrm{Cs}[\mathrm{Co}{(3\text{\ensuremath{-}}\mathrm{C}\mathrm{N}\mathrm{py})}_{2}][\mathrm{W}{(\mathrm{C}\mathrm{N})}_{8}]{\mathrm{H}}_{2}\mathrm{O}$ $(\mathrm{C}\mathrm{N}\mathrm{py}=\text{cyanopyridine})$, with two-dimensional Co-W network bridged by CN anions. We have found that the compound shows a pressure-induced charge-transfer (CT) transition at $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at room temperature, accompanied by a remarkable color change from transparent red to green. The upper critical temperature $({T}_{\mathrm{CT},\text{up}})$ for the CT transition increases at a huge rate of $250\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{GPa}$ under pressures, reflecting the concomitant significant volume change $(\ensuremath{\Delta}V∕V=0.08)$.

High‐pressure effects on vibrational modes have been investigated in crystals of squaric acid H2C4O4 (H2SQ) and its deuterated analog (D2SQ) which show two‐dimensional networks of hydrogen bonds. Specific vibrational modes in Raman and infrared spectra were observed to anomalously disappear with the application of pressures above 30 kbar in H2SQ, but not in D2SQ, indicating that the H2SQ molecule in crystal shows the asymmetric (C1h)‐to‐centrosymmetric (C4h) structure change. This is possibly caused by pressure‐induced deformation of the correlated proton potential essentially from the double‐well to single‐well type.

The dynamics of the photoinduced phase transition has been investigated for the $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}$ cyanide film, ${\mathrm{Na}}_{0.35}\mathrm{Co}[\mathrm{Fe}(\mathrm{CN}{)}_{6}{]}_{0.79}∙3.7{\mathrm{H}}_{2}\mathrm{O}$, by means of the transient absorption spectroscopy. We observed two characteristic transient bands: short-lived intermediate band (I band) at $\ensuremath{\sim}1.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and long-lived photoinduced band (PI band) at $\ensuremath{\sim}2.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. We have found that the intensity of the I band transfers to the PI band as time exceeds, and interpreted the behavior in terms of the intersystem crossing from the photocreated low-spin ${\mathrm{Co}}^{2+}$ species to the high-spin species. We further have found that the excitation spectra of these bands are qualitatively different.

We report on the near-field optical microscopic (NSOM) imaging of single-crystal Nd1/2Sr1/2MnO3 near the first-order phase transition from the CE-type charge-ordered insulator (COI) to the ferromagnetic metal (FMM) at 165 K. Using polarized light, the measurements are sensitive to twin domains through optical anisotropy and to hysteretic inhomogeneous strain associated with the phase transition. Optical evidence for strain relaxation and multiphase coexistence is observed through the transition from 150 to 165 K. The multiphase coexistence is seen as the formation of FMM "nanoneedles" with widths less than 100 nm and lengths of at least several micrometers at temperatures well below TC. The work demonstrates polarized NSOM as a technique for the study of first-order solid-state phase transformations on the nanometer spatial scale.

We have investigated the optical conductivity spectra of La2-2xSr1+2xMn2O7 (0.3

The pulse characteristic and high coherent x‐ray beam of SPring‐8 allow us to investigate dynamics of chemical reactions and phase transition of materials caused by applied field. In order to realize such direct investigation, “x‐ray pinpoint structural measurement”, which is the advanced x‐ray measurement technique in nanometer spatial scale and/or pico‐second time scale, is being developed at SPring‐8. The features of “x‐ray pinpoint structural measurement” technique are, 1) spatial resolution: ∼ 100 nm, 2) time resolution: ∼ 40 ps, and 3) measurement under the photo‐irradiation, electric field, magnetic field, high pressure and active devices. Using this technique, we will explore the novel concept and new phenomena for nanomaterials and/or devices, and also demonstrate their validity.

We investigated the effects of temperature on the carrier formation dynamics in a small-molecular blend film, 2,5-di-(2-ethylhexyl)-3,6-bis-(5''-n-hexy-[2,2',5',2'']terthiophen-5-yl)-pyrrolo[3,4-c]pyrrolo-1,4-dione (SMDPPEH)/[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). We spectroscopically determined the absolute numbers of donor () and acceptor () excitons per absorbed photon as functions of the delay time (t), in addition to the relative number of donor carries (). We found that the carrier formation dynamics is independent of temperature at 300 and 80 K: the carrier formation time (τrise = 0.4 ps) is much faster than the decay time (τdecay ≈ 2.5 ps) of donor excitons. The temperature independence strongly suggests that only excitons created near the donor–acceptor interface contribute to the carrier formation.

Layered cobalt oxide, P2-NaxCoO2, is a prototypical cathode material for sodium-ion secondary battery. We systematically investigated the rate dependence of the discharge capacity (Q) in three thin films of Na0.68CoO2 with different film thickness (d) and in-plane grain radius (r). With subtracting conventional voltage drop effect on Q, we derived an intrinsic rate dependence of Q. We found a scaling relation between the renormalized discharge rate (γ ≡ r2/DT; D and T are the Na+ diffusion constant and discharge time, respectively) and relative capacity (=Q/Q0; Q0 is the value at a low rate limit). The observed scaling relation is interpreted in terms of the Na+ intercalation process at the electrolyte-NaxCoO2 interface and Na+ diffusion process within NaxCoO2.

The femto-second time-resolved spectroscopy was performed on the heterojunction (HJ) solar cell which consists of prototypical low-band gap donor (D), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5- b′] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]] (PTB7), and the C70 acceptor (A). We spectroscopically determined the absolute number of donor exciton ( nD*), acceptor exciton ( nA*), and carrier ( nD+) per an absorbed photon against the delay time (t). At 300 K, we found that the decay time ( τdecay = 3.5 ps) of A* is much longer than the carrier formation time ( τform = 1.1 ps), indicating that the late A* component does not contribute to the carrier formation process. The elongated τform (=1.5 ps) at 80 K is ascribed to the exciton migration process, not to the exciton dissociation process.

A boron subphthalocyanine chloride (SubPc) is a bipolar molecule and is used in hetero-junction organic solar cells. Here, we investigated the carrier injection dynamics from the donor α-sexithiophene (6T) or acceptor C60 layers to the bipolar SubPc layer by means of the femtosecond time-resolved spectroscopy. We observed gradual increase of the SubPc– (SubPc+) species within ≈300 ps. The increases are interpreted in terms of the exciton diffusion within the 6T (C60) layer and subsequent electron (hole) injection at the interface. In 6T/SubPc heterojunction, the electron injection is observed even at 80 K. The robust electron injection is ascribed to the efficient charge separation within the 6T layer under photo exciation at 400 nm.