Development of the Soft X-ray AGM-AGS RIXS beamline at the Taiwan Photon Source.

We report on the development of a high-resolution and highly efficient beamline for soft X-ray resonant inelastic X-ray scattering (RIXS) located at the Taiwan Photon Source. This beamline adopts an optical design that uses an active grating monochromator (AGM) and an active grating spectrometer (AGS) to implement the energy compensation principle of grating dispersion. Active gratings are utilized to diminish defocus, coma and higher-order aberrations, as well as to decrease the slope errors caused by thermal deformation and optical polishing. The AGS is mounted on a rotatable granite platform to enable momentum-resolved RIXS measurements with scattering angles over a wide range. Several high-precision instruments developed in-house for this beamline are described briefly. The best energy resolution obtained from this AGM-AGS beamline was 12.4 meV at 530 eV, achieving a resolving power of 4.2 × 104, while the bandwidth of the incident soft X-rays was kept at 0.5 eV. To demonstrate the scientific impact of high-resolution RIXS, we present an example of momentum-resolved RIXS measurements on a high-temperature superconducting cuprate, i.e. La2-xSrxCuO4. The measurements reveal the A1g buckling phonons in superconducting cuprates, opening a new opportunity to investigate the coupling between these phonons and charge-density waves.

Doping Dependence of Collective Spin and Orbital Excitations in the Spin-1 Quantum Antiferromagnet La_{2-x}Sr_{x}NiO_{4} Observed by X Rays.

We report the first empirical demonstration that resonant inelastic x-ray scattering (RIXS) is sensitive to collective magnetic excitations in S=1 systems by probing the Ni L_{3} edge of La_{2-x}Sr_{x}NiO_{4} (x=0, 0.33, 0.45). The magnetic excitation peak is asymmetric, indicating the presence of single and multi-spin-flip excitations. As the hole doping level is increased, the zone boundary magnon energy is suppressed at a much larger rate than that in hole doped cuprates. Based on the analysis of the orbital and charge excitations observed by RIXS, we argue that this difference is related to the orbital character of the doped holes in these two families. This work establishes RIXS as a probe of fundamental magnetic interactions in nickelates opening the way towards studies of heterostructures and ultrafast pump-probe experiments.

Coulomb Correlations Intertwined with Spin and Orbital Excitations in LaCoO_{3}.

We carried out temperature-dependent (20-550 K) measurements of resonant inelastic x-ray scattering on LaCoO_{3} to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantified the renomalized crystal-field excitation energies and spin-state populations. We show that the screening of the effective on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO_{3}. The results establish that the gradual spin-state crossover is associated with a relative change of Coulomb energy versus bandwidth, leading to a Mott-type insulator-to-metal transition.

Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels.

Resonant inelastic x-ray scattering is used to investigate the electronic origin of orbital polarization in nickelate heterostructures taking LaTiO_{3}-LaNiO_{3}-3×(LaAlO_{3}), a system with exceptionally large polarization, as a model system. We find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This provides an explanation for the limited success of theoretical predictions based on tuning orbital energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena.

Origin of the large polarization in multiferroic YMnO3 thin films revealed by soft- and hard-X-ray diffraction.

We investigated the magnetic structure of an orthorhombic YMnO(3) thin film by resonant soft x-ray and hard x-ray diffraction. We observed a temperature-dependent incommensurate magnetic reflection below 45 K and a commensurate lattice-distortion reflection below 35 K. These results demonstrate that the ground state is composed of coexisting E-type and cycloidal states. Their different ordering temperatures clarify the origin of the large polarization to be caused by the E-type antiferromagnetic states in the orthorhombic YMnO(3) thin film.

Unconventional exciton evolution from the pseudogap to superconducting phases in cuprates.

Electron quasiparticles play a crucial role in simplifying the description of many-body physics in solids with surprising success. Conventional Landau's Fermi-liquid and quasiparticle theories for high-temperature superconducting cuprates have, however, received skepticism from various angles. A path-breaking framework of electron fractionalization has been established to replace the Fermi-liquid theory for systems that show the fractional quantum Hall effect and the Mott insulating phenomena; whether it captures the essential physics of the pseudogap and superconducting phases of cuprates is still an open issue. Here, we show that excitonic excitation of optimally doped Bi2Sr2CaCu2O8+δ with energy far above the superconducting-gap energy scale, about 1 eV or even higher, is unusually enhanced by the onset of superconductivity. Our finding proves the involvement of such high-energy excitons in superconductivity. Therefore, the observed enhancement in the spectral weight of excitons imposes a crucial constraint on theories for the pseudogap and superconducting mechanisms. A simple two-component fermion model which embodies electron fractionalization in the pseudogap state provides a possible mechanism of this enhancement, pointing toward a novel route for understanding the electronic structure of superconducting cuprates.

Redescription of Brachirus aspilos (Bleeker 1852), a senior synonym of four nominal species, with a note on the distribution of Dagetichthys marginatus (Boulenger 1900) (Pleuronectiformes: Soleidae).

The poorly known sole Brachirus aspilos (Bleeker 1852) is redescribed on the basis of the holotype and 48 non-type specimens from Japan, Taiwan, Philippine, Singapore, Indonesia, Papua New Guinea, and Australia. The species is characterized by the following combination of characters: dorsal-fin rays 64-76 (mode 71), anal-fin rays 51-62 (56), pored scales on straight portion of lateral line 93-126 (118); vertebrae 41-44 (43); pectoral-fin rays 4-7 (6) and 4-7 (5) on ocular and blind sides, respectively; pelvic-fin rays 4-6 (5) and 4-5 (4) on ocular and blind sides, respectively; caudal-fin rays 13-15 (14); body slightly elongate, its depth 40.0-51.0 (mean 45.5)% SL; head length 16.1-23.9 (18.6)% SL; pectoral fin on ocular side longer than that on blind side, 5.3-7.6 (6.6)% SL and 4.0-6.0 (4.8)% SL, respectively; pelvic fin on ocular side longer than that on blind side, 4.9-7.4 (6.0)% SL and 4.3-7.5 (5.8)% SL, respectively; body depth below lateral line 21.7-27.1 (23.4)% SL; lips without labial papillae; eyes separated by scaled interorbital space; cycloid or weakly ctenoid scales on blind side; body on ocular side uniformly brown or grey with dark vermiculation, some small white blotches along dorsal- and anal-fin bases, or without remarkable pattern. Brachirus dicholepis (Peters 1877), B. heterolepis (Bleeker 1856), B. marmoratus (Bleeker 1853), and B. sorsogonensis (Evermann Seale 1907), previously regarded as valid species, are all regarded as junior synonyms of B. aspilos. In addition, specimens previously reported as Dagetichthys marginatus (Boulenger 1900) from the western Pacific Ocean are re-identified as B. aspilos, the former species being considered restricted to South African waters.

Probing optically silent superfluid stripes in cuprates.

Unconventional superconductivity in the cuprates coexists with other types of electronic order. However, some of these orders are invisible to most experimental probes because of their symmetry. For example, the possible existence of superfluid stripes is not easily validated with linear optics, because the stripe alignment causes interlayer superconducting tunneling to vanish on average. Here we show that this frustration is removed in the nonlinear optical response. A giant terahertz third harmonic, characteristic of nonlinear Josephson tunneling, is observed in La1.885Ba0.115CuO4 above the transition temperature Tc = 13 kelvin and up to the charge-ordering temperature Tco = 55 kelvin. We model these results by hypothesizing the presence of a pair density wave condensate, in which nonlinear mixing of optically silent tunneling modes drives large dipole-carrying supercurrents.

Down-regulation of an inhibitor of cell growth, transmembrane protein 34 (TMEM34), in anaplastic thyroid cancer.

PURPOSE: Ansaplastic thyroid cancer (ATC) is one of the most lethal malignancies, but the carcinogenic mechanism of ATC has not been clarified. Recently, we performed a cDNA microarray analysis and identified transmembrane protein 34 (TMEM34) that down-regulated in anaplastic thyroid cancer cell lines (ACL)s as compared to normal thyroid tissues. METHODS: To investigate the role of TMEM34 in ATC carcinogenesis, we examined expression levels of TMEM34 in ACLs as well as differentiated thyroid cancers (DTC)s and normal human tissues. To explore the effect of TMEM34 in ATC development, cell-growth assays with KTA2 cells were performed. RESULTS: Expression of TMEM34 was down-regulated in all 11 ACLs, as compared to either normal thyroid tissues or cell lines derived from papillary or follicular thyroid cancers. TMEM34 was expressed ubiquitously in normal human tissues tested. Transfection of TMEM34 into KTA2 cells led to inhibition of cell growth. CONCLUSIONS: Our findings suggest that TMEM34 might be a tumor suppressor gene, associated with the development of ATC from DTC.

Jahn-Teller distortion driven magnetic polarons in magnetite.

The first known magnetic mineral, magnetite, has unusual properties, which have fascinated mankind for centuries; it undergoes the Verwey transition around 120 K with an abrupt change in structure and electrical conductivity. The mechanism of the Verwey transition, however, remains contentious. Here we use resonant inelastic X-ray scattering over a wide temperature range across the Verwey transition to identify and separate out the magnetic excitations derived from nominal Fe2+ and Fe3+ states. Comparison of the experimental results with crystal-field multiplet calculations shows that the spin-orbital dd excitons of the Fe2+ sites arise from a tetragonal Jahn-Teller active polaronic distortion of the Fe2+O6 octahedra. These low-energy excitations, which get weakened for temperatures above 350 K but persist at least up to 550 K, are distinct from optical excitations and are best explained as magnetic polarons.

Raman and fluorescence characteristics of resonant inelastic X-ray scattering from doped superconducting cuprates.

Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O(8+δ). Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast, the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors.

Characterization of excitatory amino acid receptors in cultured chick cerebellar neurons.

In order to characterize excitatory amino acid receptors in cultured chick cerebellar neurons, the effects of amino acid agonists on the input resistance and the antagonist specificity of the depolarization induced by each agonist were intracellularly studied. In Mg-containing medium, glutamate (especially at low doses), aspartate and N-methyl-D-aspartate not only decreased the input resistance at depolarized membrane potentials but also increased it at around the resting potential. In Mg-free medium, glutamate (high and low doses) and all other agonists simply decreased the input resistance. The effects of antagonists on amino acid-induced depolarizations in Mg-free medium were as follows: Mg and alpha-aminoadipate blocked N-methyl-D-aspartate and aspartate most strongly, glutamate and kainate moderately, and quisqualate only slightly; 2-amino-4-phosphonobutyrate antagonized N-methyl-D-aspartate most strongly, aspartate moderately and others mildly; 2-amino-5-phosphonovalerate blocked aspartate most strongly and others mildly; gamma-D-glutamylglycine blocked kainate most strongly and others moderately; and kynurenate was rather nonselective but most strongly antagonized N-methyl-D-aspartate and aspartate. These results suggest that all receptor subtypes (N-methyl-D-aspartate-, quisqualate- and kainate-types) are present in cultured chick cerebellar neurons, but their antagonist specificities are different from those in other central neurons, and also that glutamate at a low dose activates N-methyl-D-aspartate receptors, while it acts on quisqualate receptors at a high dose.

3-Methylhistidine content and pH dependency of ATPase activity of adult and embryonic chicken cardiac ventricular myosins.

A distinct difference in the 3-methylhistidine (3-MeHis) content and the pH-dependency curve for calcium-activated adenosine triphosphatase (Ca-ATPase) activity was observed between chicken and mammalian cardiac ventricular myosins. The 3-MeHis content and pH dependency of the Ca-ATPase activity of myosins from adult and embryonic chicken cardiac ventricular muscles and chicken fast white and slow red muscles were almost the same.

Presence of smooth muscle myosin-like protein on liver cells.

Antiserum against purified chicken smooth muscle myosin was obtained from rabbits. The serum was specific for smooth muscle myosin and did not react with myosins from fast and slow skeletal muscle or cardiac muscle. Using this specific antibody, the location of smooth muscle myosin-like protein was studied by double antibody immunofluorescence microscopy with sections of chicken liver tissue. Marked fluorescence was demonstrated along the sinusoids of hepatic tissue and the vascular walls. The findings in this study suggest that a myosin-like protein, which is immunologically similar to the myosin from smooth muscle but not to myosins from skeletal or cardiac muscle would exist on the sinusoidal surface of liver cells.

Effect of calcium ions on the sensitivities of cultured cerebellar neurons to glutamate and aspartate.

Iontophoretically applied glutamate and aspartate induced depolarizations in immature (6-13 days in culture) and mature (25-45 days) cultured chick cerebellar neurons, immature neurons being less sensitive. The input resistances of the neurons were variously changed by these amino acids. Reversal potentials of the depolarizations induced by both amino acids were similar in either immature or mature neurons. The population of amino acid-sensitive neurons increased with maturation. In mature neurons, the amplitude of glutamate- or aspartate-induced depolarization was decreased by addition of 10 mM Ca2+ to normal Tyrode's solution, aspartate responses being decreased more greatly. In low-Na+ solution (2.7 mM), however, high Ca2+ significantly enhanced amino acid-induced depolarizations. In immature neurons, on the other hand, the amplitude of glutamate- or aspartate-induced depolarization was drastically and consistently increased when 10 mM Ca2+ was added either to normal solution or to the low-Na+ solution. These enhancing actions of Ca2+ were abolished by Mn2+, but only partially by 10 mM glutamic acid diethylester or 1 mM D-alpha-aminoadipate, though responses to both amino acids in normal solution were blocked by these antagonists at the same concentrations. These results suggest that calcium ions enhance the effect of glutamate and aspartate in immature neurons, possibly by interacting with the ionophores involved in amino acid responses.

Effects of noradrenaline on the responsiveness of cultured cerebellar neurons to excitatory amino acids.

The effects of noradrenaline (NA) on the responsiveness of cultured cerebellar neurons to excitatory amino acids were intracellularly investigated. NA applied to external medium to a final concentration of 10 microM or lower slightly decreased the firing frequency of spontaneous spikes, induced a small hyperpolarization or slightly increased the input resistance of Purkinje cells. In addition, bath-applied NA was found to enhance the depolarizations induced by iontophoretically applied glutamate and aspartate but to a smaller extent for the latter. These direct and modulating effects of NA were also observed when NA was applied by iontophoresis. The sites sensitive to iontophoresed NA were found to be not uniformly distributed but localized in restricted regions on individual Purkinje cells. The enhancement by NA of the glutamate or aspartate response was blocked by beta-adrenergic antagonists, propranolol or pindolol, and extracellularly applied cAMP mimicked the NA action. These results suggest the possibility that NA physiologically modulates excitatory amino acid-mediating synaptic transmission in the cerebellum probably by acting on beta-rather than alpha-adrenergic receptors.

Participation of cyclic adenosine monophosphate and beta-adrenergic receptors in the facilitatory effect of noradrenaline on the response of cultured cerebellar neurons to glutamate.

For the purpose of examining possible involvement of the cyclic adenosine monophosphate (cAMP) system and adrenergic receptors in the modulatory effect of noradrenaline (NA) on the glutamate-induced depolarizing response, the effects of dibutyryl cAMP (DBcAMP), forskolin, theophylline, clonidine, isoproterenol and propranolol were intracellularly investigated in the cerebellar neurons cultured from chick embryos. Not only NA-induced hyperpolarization and increase in input resistance but also the facilitatory effect of NA on the glutamate response were mimicked by DBcAMP and isoproterenol. This facilitatory effect of DBcAMP was enhanced by theophylline or forskolin, while that of isoproterenol was antagonized by propranolol. Clonidine suppressed glutamate-induced depolarization. These results that the enhancing action of NA on the responsiveness of cultured cerebellar neurons to excitatory amino acids is mediated by beta-adrenergic receptors and the intracellular cAMP system.

Development of sensitivity to GABA and glycine in cultured cerebellar neurons.

The effects of iontophoretically applied gamma-aminobutyric acid (GABA) and glycine on developing cerebellar neurons cultured for 7-40 days were intracellularly investigated. All neurons tested dose-dependently responded to both GABA and glycine. In mature neurons (after 25 days in culture) these amino acids inhibited spontaneous spikes, decreased the membrane input resistance and induced either hyperpolarization or depolarization of membrane potential. The mean reversal potential was -47 mV for GABA and -43 mV for glycine. Immature neurons, 7-12 days in culture, which were not spontaneously firing, also behaved in a similar manner as the mature ones, though the membrane resistance was not so largely changed by GABA or glycine and the reversal potential was more positive (-39 mV for GABA, -37 mV for glycine). These reversal potentials were shifted toward 0 mV by lowering the external Cl- concentration in either mature or immature neurons. The effects of GABA and glycine on mature or immature neurons were more or less inhibited by all of picrotoxin, bicuculline and strychnine. The effective concentrations of these antagonists, however, were lower in general in immature neurons. In mature neurons, picrotoxin and bicuculline became more selective to GABA than glycine and strychnine became more selective to glycine than GABA. These results suggest that sensitivities to GABA and glycine differentiate into selective types in the course of maturing of cerebellar cultured neurons.

Electrophysiological and pharmacological actions of N-acetylaspartylglutamate intracellularly studied in cultured chick cerebellar neurons.

The electrophysiological and pharmacological actions of N-acetylaspartylglutamate (NAAG) in cultured chick cerebellar neurons were intracellularly investigated in comparison with L-aspartate (ASP) and L-glutamate (GLU). Iontophoretically applied NAAG dose-dependently induced depolarizations associated with increases in spike discharge and changes in membrane conductance. Relative excitatory potencies seemed to be GLU greater than ASP greater than or equal to NAAG. The voltage-dependent increase in input resistance observable in the presence of Mg ions was most notable for ASP, moderate for NAAG and least for GLU. The reversal potential of NAAG-induced depolarization was at about 0 mV and similar to that for ASP or GLU, indicating primary concern of Na+/K+-conductances to the NAAG action. Mg ions depressed the actions of ASP and NAAG more strongly than the GLU action. 2-Amino-5-phosphonovalerate (APV) and D-alpha-aminoadipate antagonized the actions of ASP and NAAG more effectively than the GLU action. 2-Amino-4-phosphonobutyrate (APB) and glutamic acid diethylester showed rather non-selective antagonisms to NAAG, ASP and GLU. These results suggest that NAAG is excitatory to cultured chick cerebellar neurons and functionally resembles ASP or is intermediate between ASP and GLU, and may also support the suggested candidacy of NAAG for a neurotransmitter in the CNS.

Subtypes of adrenergic receptors and intracellular mechanisms involved in modulatory effects of noradrenaline on glutamate.

We have previously reported that the response of cultured chick cerebellar neurons to glutamate is enhanced by noradrenaline (NA) or isoproterenol and suppressed by clonidine. The present study was carried out to further specify the adrenergic receptor subtypes involved in the facilitatory effect of NA or isoproterenol and the suppressive effect of clonidine, and to examine the intracellular mechanisms underlying these modulatory effects of NA. The clonidine effect, which was mimicked by NA iontophoresed with large ejecting currents, was blocked by yohimbine and tolazoline (alpha 2 antagonists) and also by dibutyryl cyclic AMP or forskolin which augmented the glutamate response by itself. Prazosin, an alpha 1 receptor antagonist did not block the clonidine effect. NA- or isoproterenol-induced facilitation, which was mimicked by denopamine (beta 1 agonist), was antagonized by acebutolol (beta 1 antagonist) and not by ICI 118,551 (beta 2 antagonist). Pretreatment of neurons with pertussis toxin for more than 24 h blocked the suppressive action of clonidine without affecting the facilitatory action of isoproterenol. Furthermore, intracellular injection of GDP beta S inhibited the modulatory effects of either clonidine or isoproterenol. These results indicate that the facilitatory and inhibitory modulatory effects of NA may be mediated by beta 1 and alpha 2 receptors linked to cAMP systems, respectively, and the former is coupled with the stimulatory G protein (Gs) and the latter is with the inhibitory G protein (Gi).