Search

Magnetic and optical properties are investigated for potassium clusters incorporated in zeolite LTA at loading densities of K atoms between 3.5 and 7.2 per cluster, the latter of which is saturated. The Curie–Weiss law with negative Weiss temperature -35 K is seen at 3.5 atoms per cluster, and gradually approaches the Curie law as the loading density increases up to 7.2 atoms per cluster. The Curie temperature, ∼8 K at 3.5 atoms per cluster, approaches 0 K at 7.2 atoms per cluster. These results suggest that the antiferromagnetic coupling between localized magnetic moments of K clusters decreases with increasing K-loading density, and almost disappears at the K-loading density of 7.2 atoms per cluster. The insulator-like absorption tail is observed in the infrared region at any loading density, indicating that K clusters in LTA are in the Mott insulator phase. The average magnetic moment estimated from the saturation magnetization remarkably increases from 0.25 to 0.75 μB per cluster as loading density increases from 3.5 to 7.2 atoms per cluster. On the contrary, the average magnetic moment estimated from the Curie constant is ∼1.6 μB per cluster, and almost independent of the loading density. The explanation of these magnetic properties by the model of ferrimagnetism proposed in a previous paper proves difficult.

The authors report infrared near-field spectroscopy using synchrotron radiation at BL43IR, SPring-8 in the finger print region. At the microspectroscopy station, the infrared synchrotron radiation beam is focused on a cantilever probe with a 3 μm square aperture. A comb-shaped Au electrode with the width of 3 μm and the distance of 3 μm is used for the reflection measurement. The Au electrodes can be resolved at 650 cm−1 and the resolution is estimated to be λ/5.

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 reflectance R(w) of a pressure-induced superconductor SrFe2As2 has been measured under external pressure to 6 GPa and at temperatures to 8 K. Optical conductivity s(w) has been derived from the measured R(w). At ambient pressure, in the antiferromagnetic state below T_N=198 K, a pronounced feature develops in s(w) due to the opening of a spin density wave (SDW) gap, as already reported in the literature. With increasing pressure, the SDW gap feature in s(w) is progressively suppressed. At 4 GPa, where the sample is superconducting, the SDW gap feature in s(w) is strongly reduced than that at ambient pressure, but is still clearly observed. At 6 GPa, the SDW gap is completely suppressed. The pressure evolutions of the SDW gap magnitude and the spectral weight closely follow the pressure evolution of T_N., 6 pages, 4 figures

Absorption spectra are reported for BiI 3 molecules incorporated into channels of zeolite MOR and AFI. Polarized absorption spectra for the zeolite single crystals, of size about 50 μm, were measured by means of microoptical spectroscopy. The absorption spectrum of BiI 3 in MOR is different from that observed in LTA, and also shows a polarization dependent on the direction of the channel. The BiI 3 molecule is expected to have nearly C 3v symmetry even in the MOR channels, and has a preferred orientation of the molecular axis along the channel. On the other hand, no polarization dependence of BiI 3 is observed in the AFI channel, although AFI has a channel size similar to that of MOR. The cations and the framework induce the electric field inside the MOR channels, which acts as an adsorption potential for molecules. The experimental results indicate that the electric field plays an important role in the molecular orientation.

The magnetization process of potassium clusters arrayed in zeolite LTA is measured up to 14 T. This material shows ferromagnetism at certain concentrations of potassium atoms in cluster. The magnetization at ferromagnetic concentrations increases linearly with the applied magnetic field at higher fields. This result is well explained by a spin-cant model of antiferromagnet. A largeness of an estimated spin-cant angle is assigned to the Dzyaloshinsky-Moriya interaction strongly enhanced by the degeneracy of 1p-orbital of cluster.

μSR has been studied for a ferromagnetic sample of K clusters in zeolite LTA as a function of longitudinal field (LF) and temperature. Under weak LF a non-relaxing asymmetry component is produced at low temperatures, whereas at higher temperatures in the paramagnetic state a two-component relaxation is clearly observed. The data are successfully explained by assuming two different muon-stopping sites in the cubic antiferromagnet, along with a canting of the spin structure.

We report a novel insulator-insulator transition arising from the internal charge degrees of freedom in the two-dimensional quarter-filled organic salt beta-(meso-DMBEDT-TTF)2PF6. The optical conductivity spectra above Tc = 70 K display a prominent feature of the dimer-Mott insulator, characterized by a substantial growth of a dimer peak near 0.6 eV with decreasing temperature. The dimer-peak growth is rapidly quenched as soon as a peak of the charge order shows up below Tc, indicating a competition between the two insulating phases. Our infrared imaging spectroscopy has further revealed a spatially competitive electronic phases far below Tc, suggesting a nature of quantum phase transition driven by material-parameter variations., 5 pages, 4 figures, supplemental material, to be published in Phys. Rev. Lett

Optical conductivity [{delta}({omega})] of PrRu{sub 4}P{sub 12} has been studied under high pressure to 14 GPa, at low temperatures to 8 K, and at photon energies 12 meV-1.1 eV. The energy gap in {delta}({omega}) at ambient pressure, caused by a metal-insulator transition due to an unconventional charge-density-wave formation at 63 K, is gradually filled in with increasing pressure to 10 GPa. At 14 GPa and below 30 K, {delta}({omega}) exhibits a pronounced Drude-type component due to free carriers. This indicates that the initial insulating ground state at zero pressure has been turned into a metallic one at 14 GPa. This is consistent with a previous resistivity study under pressure, where the resistivity rapidly decreased with cooling below 30 K at 14 GPa. The evolution of electronic structure with pressure is discussed in terms of the hybridization between the 4f and conduction electrons.

Electron spin resonance studies are carried out for potassium clusters stabilized in cages of aluminosilicate zeolite LTA, where cages are arrayed in a simple cubic structure. The average number of s-electrons per cluster, n , is systematically changed from 0 to the saturated value of \cong7.2. For samples at 2< n , where s-electrons occupy the 1p-state of K cluster, the g value decreases remarkably from 2, indicating that an enhancement of the spin–orbit interaction occurs due to the orbital degeneracy of the 1p-state. Simultaneously, ferromagnetism is observed for samples at 2< n . The origin of the ferromagnetism is assigned to the orbital degeneracy of 1p-state followed by the enhancement of the Dzyaloshinsky–Moriya interaction between adjacent K clusters.

In order to obtain broadband near-field infrared (IR) spectra, a Fourier-transform IR spectrometer (FT-IR) and a ceramic light source were used with a scattering-type scanning near-field optical microscope (s-SNOM). To suppress the background (far-field) scattering, the distance between the scattering probe and the sample was modulated with frequency Ω by a piezo-electric actuator, and the Ω component was extracted from the signal with a lock-in detection. With Ω=30 kHz, a peak-to-peak modulation amplitude of 198 nm, and a probe with smooth surface near the tip, broadband near-field IR spectra could be obtained in the 1200-2500 cm(-1).

Optical conductivity [s(w)] of Ce-filled skutterudite CeRu4Sb12 has been measured at high pressure to 8 GPa and at low temperature, to probe the pressure evolution of its electronic structures. At ambient pressure, a mid-infrared peak at 0.1 eV was formed in s(w) at low temperature, and the spectral weight below 0.1 eV was strongly suppressed, due to a hybridization of the f electron and conduction electron states. With increasing external pressure, the mid-infrared peak shifts to higher energy, and the spectral weight below the peak was further depleted. The obtained spectral data are analyzed in comparison with band calculation result and other reported physical properties. It is shown that the electronic structure of CeRu4Sb12 becomes similar to that of a narrow-gap semiconductor under external pressure., 8 pages, 9 figures

Magnetic and optical properties of Rb clusters in aluminosilicate zeolite LTA are investigated in detail. These clusters are stabilized in supercages arrayed in a simple cubic structure. The average number of s-electrons confined in each cluster, n , is changed up to the nearly saturated value ∼4.6. At n >2, the absolute value of the negative Weiss temperature increases with increasing n . In saturated samples at n ∼4.6, ferromagnetic properties are observed below the asymptotic Curie temperature 3 K, but the fraction of the spontaneous magnetization is found to be very small and incomplete. Magnetic properties are different from those of K clusters in LTA, and discussed in relation to residual K cations.

We have studied the IR reflectance of correlated electron materials under high pressure to 20 GPa, using synchrotron radiation as a highly bright IR source. The instrumentation and examples of obtained results are briefly described.

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.

K and Na clusters are generated in zeolite FAU with an Si-to-Al ratio of 1.25. We measured magnetic susceptibility, electron}spin resonance spectrum and the optical one. Observed magnetic properties are discussed from the viewpoint of the correlated electrons and/or the narrow energy band with a properly localized nature of clusters, together with a "nite disorder e!ect. ( 2000 Elsevier Science B.V. All rights reserved.

We investigated the infrared optical spectra of an organic dimer Mott insulator $\ensuremath{\kappa}\mathrm{\text{\ensuremath{-}}}(\mathrm{BEDT}\mathrm{\text{\ensuremath{-}}}\mathrm{TTF}{)}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Cl}$, 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.

We have fabricated a metallic structure in an organic Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl. The periodic metallic domains of approximately 90$\times$90 $\mu$m$^2$ obtained by X-ray irradiation through a molybdenum mesh mask are visualized by scanning microregion infrared reflectance spectroscopy technique. No deterioration by irradiation is found in a range of nanometer to micrometer scales. We demonstrate that the present processing method is applicable for the fabrication of molecular electronic devices., Comment: 3 pages, submitted to APEX

Avascular necrosis (osteonecrosis) is a disease that results from the temporary or permanent loss of blood supply to the bone. Synchrotron FT-IR microspectroscopy has been used to study the changes in mineral and matrix content of necrotic bone. FT-IR spectroscopic analysis revealed that in necrotic bone the relative mineral/matrix ratio decreased. Spectroscopic differences were observed between normal and necrotic bones. The noticeable differences may have important implications for analyzing and evaluating death bone.

Katsuya Araki, Naoto Yagi, Yuka Ikemoto, Hisashi Yagi, Chi-Jing Choong, Hideki Hayakawa, Goichi Beck, Hisae Sumi, Harutoshi Fujimura, Taro Moriwaki, Yoshitaka Nagai, Yuji Goto & Hideki Mochizuki "Synchrotron FTIR micro-spectroscopy for structural analysis of Lewy bodies in the brain of Parkinson’s disease patients", Scientific Reports, volume 5, Article number: 17625, Springer Nature, 2015, 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.

Infrared synchrotron radiation (IR-SR) is a highly brilliant white light source. We are developing an infrared near-field spectroscopy system with an IR-SR light source. The near-field spectroscopy system previously reported comprised an atomic force microscope (AFM) and a commercial Fourier transform infrared (FTIR) spectrometer. In the present study, the configuration of the FTIR interferometer has been modified to an asymmetric one. In the asymmetric interferometer, one beam split by a beamsplitter is focused onto the tip of an AFM probe, and the other beam goes to a movable mirror. The scattered light from the probe and the light reflected by the movable mirror interfere with each other. The near-field signal is extracted by a modulation method with an AFM oscillation frequency. The signal-to-noise ratio has been improved 6-fold and the signal-to-background ratio is improved 8-fold compared with those observed in the previous system.

Optical conductivity σ(ω) of CeCoIn5 has been measured under high pressure to 8 GPa and at low temperatures to 6 K, to study the pressure evolution of the conduction (c)-f electron hybridized state near the Fermi level. At ambient pressure, CeCoIn5 is a heavy fermion superconductor with Tc=2.3 K, and has moderately strong c-f hybridization. σ(ω) at ambient pressure shows a marked infrared peak due to optical excitations involving the c-f hybridized state. With increasing pressure, the infrared peak becomes broader, and its center shifts to higher energy. This result indicates that the large density of states of the c-f hybridized state becomes broader with increasing pressure, and that the peak of the density of states shifts away from the Fermi level. Althouth such pressure evolution of the c-f hybridized state had been widely assumed on the basis of theoretical consideration, the present optical result demonstrates it clearly and directly.

SPring-8, which is the third generation X-ray light source and has the largest storage ring among synchrotron radiation facilities in the world has been proved also to provide two order of magnitude higher infrared photon fluxes than a conventional globar lamp. We completed the construction of the beamline, BL43IR which is dedicated only to infrared spectroscopy and developed a far-infrared spectroscopic system under high pressure up to 15 GPa by using a diamond anvil cell combined with IR-microscopy. In this paper, we report the recent results of study on the change in the electronic structure of transition metal compounds due to a pressure-induced electronic phase transition as the example of our recent progress in the application of infrared synchrotron radiation to solid state physics.

CuIr/sub 2/Se/sub 4/ is a metal at atmospheric pressure, but shows a stabilization of insulating phase from metal phase under high pressure. In order to study the electronic structure very near to the Fermi level (E/sub F/) and its change due to a metal-insulator transition (MIT), we measured the temperature and pressure dependence of optical spectra on polycrystalline spinel compound CuIr/sub 2/Se/sub 4/ under high pressure. At ambient pressure, the growth of the peak structure at /spl sim/0.2 eV corresponding to the formation of a pseudo-gap state was found with decrease in temperature but a Drude component still remained even at 8 K. Under pressure, the /spl sigma/-spectra changed much from that at ambient pressure. At 0.5 GPa, two peaks at /spl sim/0.2 eV and at /spl sim/0.8 eV corresponding to interband transitions were found together with a Drude component. With pressure, the peak at /spl sim/0.2 eV that were assigned to the electronic excitation across the hybridization bands of Ir5d and Se4p states lost its intensity as the Drude component did at 5.5 GPa. At 6.0 GPa, the spectrum showed the disappearance of the Drude component and the shift to high energy of two interband transition peaks. Our experiments indicated clearly the pressure-induced MIT due to the increase in the degree of hybridization.

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. Detailed energy, temperature, and excitation power dependences of the photoinduced absorption are reported. This photo-induced absorption is attributed to the intragap excitations of the photogenerated carriers. The data show the existence of a high density of in-gap states for the photocarriers, which extends over a wide energy range starting from the conduction and valence band edges., Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jpn

Optical gain spectra are investigated for Zn 0.7 Cd 0.3 Se/ZnSe single quantumj well laser structures at room temperature by varying the optical excitation length. An optical gain of several tens of cm -3 is achieved for 100 kW/cm 2 at the exciton tail region. The photoluminescence excitation spectrum is also measured to determine exciton resonances. The gain mechanism is discussed in terms of phase-space filling of an inhomogeneously broadened exciton state.

By means of a scanning micro-region infrared reflectance spectroscopy, we study a real-space imaging of local electronic states in a 4d-electron transition-metal oxide Ca2RuO4. Our spectroscopic imaging shows a macroscopic spatial inhomogeneity of energy gap in the orbital-ordered insulating phase below 360 K. The result includes no metal–insulator domains but rather an inhomogeneous distribution of the energy gap. We demonstrate that the gap distribution is intimately correlated with local crystalline disorders, indicating a strong electron–lattice coupling expected in orbital-ordered systems. Such a disorder-sensitive infrared spectroscopy is reminiscent of a disorder effect on charge/orbital order in 3d oxides, implying a significant role of quenched disorder in various orbital-ordered systems.

Cadmium halides (CdCl2, CdBr2 and CdI2) crystallize in a layered structure in which a Cd2þ-ion plane is sandwiched between two halogen ion planes. The fundamental layers pile up along the crystal c-axis to make up cadmium halide crystals. When doping a small amount of metal cyanide into these cadmium halide crystals, cyanic ions are supposed to be substituted for the halogen ions. In the present work, polarized infrared (IR) absorption has been investigated on CN centers doped in CdI2 crystals. For interpretation of these IR absorption, interaction of the CN elastic dipole with the local electric field in the crystal must be taken into account: A strong local electric uniaxial crystal field along the c-axis could arrange the CN molecular axis along this axis of the crystal. On the other hand, IR absorption and luminescence on CN centers in alkali halide crystals have been studied extensively without any indication of such arrangement of the dipole centers. The crystals were grown from melt in a vacuum sealed quartz ampule filled with CdI2 powder containing impurity Hg(CN)2 of 0.1mol% as an impurity. The CN -ion would substitute for a host I -ion. The specimens were cleaved in the size of 10 10 5mm from the CdI2 crystal ingot. The concentration of Hg(CN)2 in the specimens was not determined in the present study. The values of concentration in the following are those in the melt. The crystal samples were mounted on a copper holder of a closed-cycle He refrigerator and were cooled down to 6K. The present experiments were performed at the absorption and reflection spectroscopy station on the beamline BL43IR of the synchrotron radiation facility SPring-8, Hyogo, Japan. Polarized IR absorption spectra were measured by using a FT-IR spectrometer (Bruker IFS 120HR). The spectral resolution of this spectrometer was set for 0.025 cm 1 at 2000 cm . An internal globar lamp of the FT-IR spectrometer was used as the light source. Figure 1 shows the IR absorption spectra of CdI2:Hg(CN)2 (0.1mol%) in the range of 2060–2160 cm 1 for the polarization parallel (E k c) and perpendicular (E ? c) to the c-axis. Polarized light with E k c or E ? c was led on the polished crystal surface along the direction perpendicular to the crystal c-axis (E is the electric field vector of polarized light). The interference pattern due to BaF2 windows of the cryostat appears on the background of both spectra. Dichroism between the E k c and E ? c spectra is remarkable: All absorption peaks are observed only in the polarization of E k c. As described above, the CdI2 crystal has the uniaxial crystal field in the direction along the c-axis. The dichroic absorption results show that the CN -ions in the I -ion planes are arranged with their electric dipole axes parallel to the crystal c-axis. In addition, the full width at half-maximum (0.07 cm ) of the absorption lines is much narrower than those ( 5 cm ) in alkali halides. The rotational motion of CN molecules is restrained by the local uniaxial electric field along the c-axis in the CdI2 crystal. The local uniaxial electric field at halogen ion sites comes from Cd2þ-ion planes with positive charge and I -ion planes with negative charge. The absorption peaks are classified into two groups. The one is of sharp doublet peaks (2082.1, 2084.8 cm ) in the low energy region. These peaks are attributed to CN -ions simply substituted for host I -ions, which are called Isolated-CN centers [see Figs. 2(a) and 2(a0)]. They correspond to the absorption peak due to substitutional CN ions for I -ions in alkali-iodides, e.g., the peak observed at Fig. 1. The IR absorption spectra of CdI2 doped CN measured at 6K. Upper and lower spectrum is E k c and E ? c, respectively.

Infrared (IR) spectroscopy is a versatile analytical method and nano-scale spatial resolution could be achieved by scattering type near-field optical microscopy (s-SNOM). The spectral bandwidth was, however, limited to approximately 300 cm(-1) with a laser light source. In the present study, the development of a broadband mid-IR near-field spectroscopy with a ceramic light source is demonstrated. A much wider bandwidth (at least 3000 to 1000 cm(-1)) is achieved with a ceramic light source. The experimental data on quartz Si-O phonon resonance bands are well reproduced by theoretical simulations indicating the validity of the present broadband near-field IR spectroscopy.

Molecular conductors consisting of “tight dimers” with short intermolecular distances have been studied from the viewpoint of the 1/2-filled picture. Triclinic -EtMe 3 P[Pd(dmit) 2 ] 2 [dmit = 1,3-...

Infrared reflectance spectroscopy has been used to probe the pressure evolution of metal–insulator (MI) transition in PrRu 4 P 12 up to 14 GPa. The decrease of reflectance at low temperatures, which is due to an energy gap associated with the MI transition, is almost unchanged with pressure up to 10 GPa. This decrease of reflectance, however, is strongly suppressed at 14 GPa, and an increase of reflectance is observed below 30 K. This result indicates that the MI transition of PrRu 4 P 12 has been suppressed at 14 GPa.

Far-infrared spectroscopy has been performed on [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic) single crystals, to probe changes in the molecular vibrations upon the photoinduced and temperature-induced spin crossovers. Synchrotron radiation has been used as the farinfrared source to overcome the strong absorption and the small sizes of the samples. Absorption lines due to FeN6 cluster vibrations, observed below 400 cm-1, show strong intensity variations upon the crossover due to the deformation of FeN6 between high-spin and low-spin states. However, they remain almost unchanged between the photo- and temperature-induced high-spin states. This is in sharp contrast to the lines at 500-700 cm-1 due to intramolecular vibrations of the picolylamine ligands, which show marked variations between the two high-spin states. It is concluded that the most important microscopic difference between the two high-spin states arises from the ligands, which is likely to reflect different states of intermolecular bonding between them., Comment: 10 pages, 4 figures

We embedded CdSe nanocrstallites into a porous glass with a diffusion process. Using picosecond time resolved luminescence spectrum technique, we investigated the electron dynamics in the CdSe microcrystallites in porous glass. The luminescence decay of our sample has a fast component decay sensitive to temperature. For a sample of CdSe microcrystallites with an average size of 25 Å diameter, the fast decay is 50 ps at 77 K, and is 100 ps at 2 K. With a simple three level model, the luminescence decay is simulated. The temperature dependence of luminescence decay results from nonradiative process.