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New developments in the field of cognitive sciences and eye tracking technology has allowed for more direct study of underlying cognitive processes occurring during task performance. First, eye tracking technology provides a continuous measure of pupil dilation, an indicator of cognitive effort during task performance. Second, it provides a measure of scanning patterns, providing insight as to how and where cognitive effort is directed. In this study 57 subjects were eye tracked as they performed three sessions on a dual-attention task involving monitoring gauges and comparing equations. Additional measures included performance and self-report measures of self-efficacy, and cognitive interference. The objective eye tracking measures corroborated and expanded on previously established relationships between cognitive processing, cognitive interference, self-efficacy, and performance.

We present the data from ultrahigh-resolution laser-excited photoemission spectroscopy on a newly discovered noncentrosymmetric superconcluctor Mg(10)Ir(19)B(16). We observed the evidences for the opening of superconducting gap where numerical fittings show that isotropic s-wave model can satisfactorily explain the behavior of spectra near the Fermi level. We also present the valence band photoemission spectrum and B K fluorescence spectrum to discuss the basic electronic structure of Mg(10)Ir(19)B(16). (C) 2009 Elsevier B.V. All rights reserved.

The authors have investigated the temperature variation of optical spectra comparatively for an oxygenated nonsuperconducting and a reduced superconducting crystal of Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4+y}. Anomalous gap-like structure as large as 0.3 eV has been observed in the optical conductivity spectrum of the oxygenated crystal with lowering temperature from 340 K, while little temperature-variation has been observed for the reduced crystal. Furthermore, anomalies in lattice dynamics have been observed only for the oxygenated crystal in far-infrared spectra. These spectral signatures have shown parallel temperature-dependence, signaling a possible charge ordering in the oxygenated nonsuperconducting crystal.

In Fe-based superconductors, electron doping is often realized by the substitution of transition-metal atoms for Fe. In order to investigate how the electronic structure of the parent compound is influenced by Zn substitution, which supplies nominally four extra electrons per substituted atom but is expected to induce the strongest impurity potential among the transition-metal atoms, we have performed an angle-resolved photoemission spectroscopy measurement on Ba(Fe${}_{1\ensuremath{-}x}$Zn${}_{x}$)${}_{2}$As${}_{2}$ (Zn-122). In Zn-122, the temperature dependence of the resistivity shows a kink around $T\ensuremath{\sim}$ 135 K, indicating antiferromagnetic order below the N$\stackrel{\ifmmode \acute{}\else \'{}\fi{}}{\mathrm{e}}$el temperature of ${T}_{\mathrm{N}}\ensuremath{\sim}$ 135 K. In fact, folded Fermi surfaces (FSs) similar to those of the parent compound have been observed below ${T}_{\mathrm{N}}$. The hole and electron FS volumes are, therefore, different from those expected from the rigid-band model. The results can be understood if all the extra electrons occupy the Zn 3$d$ state $\ensuremath{\sim}$10 eV below the Fermi level and do not participate in the formation of the FSs.

We have investigated the temperature variation of optical spectra for single crystals of Nd 2-x Ce x CuO 4 (0.05 < x ≤ 0.15). While little temperature variation has been observed in the optical spectrum of the x = 0.15 crystal, we have found a notable pseudogap as large as 0.2-0.4 eV at low temperature for the underdoped crystals (x < 0.15). Drude-like response also evolves concomitantly with the pseudogap formation. The onset temperature (T*) of the pseudogap decreases with electron doping. The origin of the pseudogap has been ascribed to the antiferromagnetic correlation.

Charge dynamics and its critical behavior are investigated near the metal-insulator transition of layered-nickelate ${R}_{2\ensuremath{-}x}$Sr${}_{x}$NiO${}_{4}$ ($R=\mathrm{Nd}$, Eu). The polarized x-ray absorption spectroscopy experiment clearly shows the multiorbital nature which enables the ${x}^{2}\ensuremath{-}{y}^{2}$-orbital-based checkerboard-type charge ordering or correlation to persist up to the critical doping region ($x\ensuremath{\sim}1$). In the barely metallic region proximate to the charge-ordered insulating phase, the nominal carrier density estimated from the Hall coefficient markedly decreases in accord with development of the pseudogap structure in the optical conductivity spectrum, while the effective mass is least enhanced. The present findings combined with the results of recent angle-resolved photoemission spectroscopy show that the pseudogap in the metal-insulator critical state evolves due to the checkerboard-type charge correlation to extinguish the coherent-motion carriers in a characteristic momentum (k)-dependent manner with lowering temperature.

Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results., The physical properties of organic metals have generally been described in terms of a highly correlated Luttinger liquid. Using angle-resolved photoelectron spectroscopy, Kiss et al. measure the Fermi surface of (BEDT-TTF)3Br(pBIB), and find that, in contrast to other systems, it can be described as a Fermi liquid.

We investigate the two-dimensional (2D) highly spin-polarized electron accumulation layers commonly appearing near the surface of n-type polar semiconductors BiTeX (X = I, Br, and Cl) by angular-resolved photoemission spectroscopy. Due to the polarity and the strong spin-orbit interaction built in the bulk atomic configurations, the quantized conduction-band subbands show giant Rashba-type spin-splitting. The characteristic 2D confinement effect is clearly observed also in the valence-bands down to the binding energy of 4 eV. The X-dependent Rashba spin-orbit coupling is directly estimated from the observed spin-split subbands, which roughly scales with the inverse of the band-gap size in BiTeX., Comment: 15 pages 4 figures

In layered polar semiconductor BiTeI, giant Rashba-type spin-split band dispersions show up due to the crystal structure asymmetry and the strong spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band structures of BiTeI using the bulk-sensitive $h\nu$-dependent soft x-ray angle resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is shown to be well reproducible by the first-principles calculations, with huge spin splittings of ${\sim}300$ meV at the conduction-band-minimum and valence-band-maximum located in the $k_z=\pi/c$ plane. It provides the first direct experimental evidence of the 3D Rashba-type spin splitting in a bulk compound., Comment: 9 pages, 4 figures

The three-dimensional Fermi-surface structure of hole-doped metallic layered nickelate Eu${}_{2\ensuremath{-}x}$Sr${}_{x}$NiO${}_{4}$ ($x=1.1$), an important counterpart to the isostructural superconducting cuprate La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$, is investigated by energy-dependent soft-x-ray angle-resolved photoemission spectroscopy. In addition to a large cylindrical hole Fermi surface analogous to the cuprates, we observe a $\ensuremath{\Gamma}$-centered $3{z}^{2}\ensuremath{-}{r}^{2}$-derived small electron pocket. This finding demonstrates that in the layered nickelate the $3{z}^{2}\ensuremath{-}{r}^{2}$ band resides close to the ${x}^{2}\ensuremath{-}{y}^{2}$ one in energy. The resultant multiband feature with varying orbital character as revealed may strongly work against the emergence of the high-temperature superconductivity.

We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate ${\mathrm{Sm}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$. The data show the existence of a nodal hole-pocket Fermi surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferrmagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole pocket is compatible with a $d$-wave symmetry.

Time-resolved photoelectron spectroscopy (trPES) can directly detect transient electronic structure, thus bringing out its promising potential to clarify nonequilibrium processes arising in condensed matters. Here we report the result of core-level trPES on 1$T$-TaS${}_{2}$, realized by developing a high-intensity 60-eV laser obtained by high-order harmonic generation. Ta$4f$ core-level trPES offers the transient amplitude of the charge-density wave (CDW), via the site-selective and real-time observation of Ta electrons. The present result indicates an ultrafast photoinduced melting and recovery of CDW amplitude, followed by a peculiar long-life oscillation (i.e., collective amplitudon excitation) accompanying the transfer of electrons among adjacent Ta atoms. core-level trPES offers a broad range of opportunities for investigating the ultrafast atom-specific electron dynamics in photorelated phenomena of interest.

We have investigated charge dynamics and electronic structures for single crystals of metallic layered nickelates, ${R}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Nd},\mathrm{Eu}$), isostructural to ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$. Angle-resolved photoemission spectroscopy on the barely metallic ${\mathrm{Eu}}_{0.9}{\mathrm{Sr}}_{1.1}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Eu}$, $x=1.1$) has revealed a large hole surface of ${x}^{2}\ensuremath{-}{y}^{2}$ character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped ($xl0.1$) cuprates, although the antiferromagnetic interactions are 1 order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered nickelate arises from the real-space charge correlation.

Electronic structures of the quantum critical superconductor $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}{\mathrm{YbAlB}}_{4}$ and its polymorph $\ensuremath{\alpha}\mathrm{\text{\ensuremath{-}}}{\mathrm{YbAlB}}_{4}$ are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb $3d$ core level spectra, the values of the Yb valence are estimated to be $\ensuremath{\sim}2.73$ and $\ensuremath{\sim}2.75$ for $\ensuremath{\alpha}$- and $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}{\mathrm{YbAlB}}_{4}$, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show ${\mathrm{Yb}}^{2+}$ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}{\mathrm{YbAlB}}_{4}$.

We investigate the electronic structure of Chromium Nitride (CrN) across the first-order magneto-structural transition at T_N ~ 286 K. Resonant photoemission spectroscopy shows a gap in the 3d partial density of states at the Fermi level and an On-site Coulomb energy U ~ 4.5 eV, indicating strong electron-electron correlations. Bulk-sensitive high resolution (6 meV) laser photoemission reveals a clear Fermi edge indicating an antiferromagnetic metal below T_N. Hard x-ray Cr 2p core-level spectra show T-dependent changes across T_N which originate from screening due to coherent states as substantiated by cluster model calculations using the experimentally observed U. The electrical resistivity confirms an insulator above T_N (E_g ~ 70 meV) which becomes a disordered metal below T_N. The results indicate CrN transforms from a correlated insulator to an antiferromagnetic metal, coupled to the magneto-structural transition., Submitted to Physical Review Letters (February 2010) 11 pages, 3 figures in the main text, 1 Supplementary Information

Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature (T) dependence of the electronic structure in BaFe2As2 across the magnetostructural transition at T{N} approximately 140 K. A drastic transformation in Fermi surface (FS) shape across T{N} is observed, as expected by first-principles band calculations. Polarization-dependent ARPES and band calculations consistently indicate that the observed FSs at k{z} approximately pi in the low-T antiferromagnetic state are dominated by the Fe3d{zx} orbital, leading to the twofold electronic structure. These results indicate that magnetostructural transition in BaFe2As2 accompanies orbital-dependent modifications in the electronic structure.

We report on the electronic structure of the perovskite oxide CaCrO3 using valence-band, core-level, and Cr 2p - 3d resonant photoemission spectroscopy (PES). Despite its antiferromagnetic order, a clear Fermi edge characteristic of a metal with dominant Cr 3d character is observed in the valence band spectrum. The Cr 3d single particle density of states are spread over 2 eV, with the photoemission spectral weight distributed in two peaks centered at ~ 1.2 eV and 0.2 eV below EF, suggestive of the coherent and incoherent states resulting from strong electron-electron correlations. Resonant PES across the Cr 2p - 3d threshold identifies a 'two-hole' correlation satellite and yields an on-site Coulomb energy U ~4.8 eV. The metallic DOS at EF is also reflected through the presence of a well-screened feature at low binding energy side of the Cr 2p core-level spectrum. X-ray absorption spectroscopy (XAS) at Cr L3,2 and O K edges exhibit small temperature dependent changes that point towards a small change in Cr-O hybridization. The multiplet splitting in Cr 2p core level spectrum as well as the spectral shape of the Cr XAS can be reproduced using cluster model calculations which favour a negative value for charge transfer energy between the Cr 3d and O 2p states. The overall results indicate that CaCrO3 is a strongly hybridized antiferromagnetic metal, lying in the regime intermediate to Mott-Hubbard and charge-transfer systems.

We have studied the momentum dependence of the energy gap of Bi2(Sr,R)2CuOy by angleresolved photoemission spectroscopy (ARPES), particularly focusing on the difference between R=La and Eu. By comparing the gap function and characteristic temperatures between the two sets of samples, we show that there exist three distinct energy scales, {\Delta}pg, {\Delta}sc0, and {\Delta}eff sc0, which correspond to T* (pseudogap temperature), Tonset (onset temperature of fluctuating superconductivity), and Tc (critical temperature of coherent superconductivity). The results not only support the existence of a pseudogap state below T* that competes with superconductivity but also the duality of competition and superconducting fluctuation at momenta around the antinode below Tonset., Comment: accepted in Phys. Rev. B

Low-energy electronic structure of optimally doped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is investigated using laser-excited angle-resolved photoemission spectroscopy. The surface state and the CuO chain band that usually overlap the ${\text{CuO}}_{2}$ plane derived bands are not detected, thus enabling a clear observation of the bulk superconducting state. The observed bilayer splitting of the Fermi surface is $\ensuremath{\sim}0.08\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ along $(0,0)\ensuremath{-}(\ensuremath{\pi},\ensuremath{\pi})$ direction, significantly larger than ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$. The kink structure of the band dispersion reflecting the renormalization effect at $\ensuremath{\sim}60\text{ }\text{meV}$ shows up similarly as in other hole-doped cuprates. The momentum dependence of the superconducting gap shows ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave-like amplitude but exhibits a nonzero minimum of $\ensuremath{\sim}12\text{ }\text{meV}$ along the $(0,0)\ensuremath{-}(\ensuremath{\pi},\ensuremath{\pi})$ direction. Possible origins of such an unexpected ``nodeless'' gap behavior are discussed.

We have studied the mass renormalization in Ca2-xSrxRuO4 (x=0.2) using high-resolution angle-resolved photoemission spectroscopy. We observed precise band dispersions near the Fermi level (E_{F}) and the corresponding Fermi surfaces. A characteristic flat band with approximately 4 meV dispersion accompanying sharp quasiparticle (QP) peaks shows up in a limited momentum region around (pi, 0). The QP peak rapidly evolves below the crossover temperature T;{*} approximately 20 K, which agrees well with the mass enhancement behavior indicated by thermal, magnetic, and transport properties. We discuss the origin of the mass renormalization in relation to the local flat band at (pi, 0) possibly derived from the gamma (d_{xy}) band.

We have performed a temperature-dependent angle-integrated laser photoemission study of iron oxypnictide superconductors LaFeAsO:F and LaFePO:F exhibiting critical-transition temperatures (${T}_{c}$'s) of 26 and 5 K, respectively. We find that high-${T}_{c}$ LaFeAsO:F exhibits a temperature-dependent pseudogaplike feature extending over $\ensuremath{\sim}0.1\text{ }\text{eV}$ about the Fermi level at 250 K, whereas such a feature is absent in low-${T}_{c}$ LaFePO:F. We also find $\ensuremath{\sim}20\text{-meV}$ pseudogaplike features and signatures of superconducting gaps in both LaFeAsO:F and LaFePO:F. We discuss the possible origins of the unusual pseudogaplike features through comparison with the high-${T}_{c}$ cuprates.

We study electron dynamics in graphite with time resolved photoemission spectroscopy (TRPES). Using the fourth harmonic (5.95 eV) and fundamental of a Ti:sapphire laser as a pump-probe, respectively, we observe a biexponential decay of excited electrons

Laser-excited photoemission spectroscopy is used to show that the doped carriers in metallic or superconducting diamond couple strongly to the lattice via high-energy ($\ensuremath{\sim}150\text{ }\text{ }\mathrm{meV}$) optical phonons, with direct observations of localized Franck-Condon multiphonon sidebands appearing as Fermi-edge replicas. It exhibits a temperature-dependent spectral weight transfer from higher to lower energy sidebands and zero-phonon Fermi-edge states. The quantified coupling strength shows a systematic increase on lowering temperature, implicating its relation to the normal state transport and superconductivity.

We investigate the doping dependent low energy, low temperature ($T$ = 5 K) properties of nodal quasiparticles in the d-wave superconductor Bi$_{2.1}$Sr$_{1.9}$CaCu$_2$O$_{8+\delta}$ (Bi2212). By utilizing ultrahigh resolution laser-excited angle-resolved photoemission spectroscopy, we obtain precise band dispersions near $E_{F}$, mean free paths and scattering rates ($\Gamma$) of quasiparticles. For optimally and overdoped, we obtain very sharp quasiparticle peaks of 8 meV and 6 meV full-width at half-maximum, respectively, in accord with terahertz conductivity. For all doping levels, we find the energy-dependence of $\Gamma \sim |\omega |$, while $\Gamma$($\omega =0$) shows a monotonic increase from overdoping to underdoping. The doping dependence suggests the role of electronic inhomogeneity on the nodal quasiparticle scattering at low temperature (5 K $\lsim 0.07T_{\rm c}$), pronounced in the underdoped region.

We have performed temperature- (T-)dependent laser-photoemission spectroscopy of the antiferromagnetic (AF) superconductor ErNi 2 B 2 C to study the electronic-structure evolution reflecting the interplay between antiferromagnetism and superconductivity. The spectra at the superconducting (SC) phase show a very broad spectral shape. A T-dependent SC gap shows a sudden deviation from the BCS prediction just below T N . This observation can be explained well by the theoretical model and thus represents the characteristic bulk electronic structure of the AF SC phase for the first time.

We have performed soft x-ray and ultrahigh-resolution laser-excited photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to band structure calculations and yields a reasonable assignment of partial densities of states. However, the sharp peak near the Fermi level slightly deviates from the calculated energy position, giving rise to the necessity of self-energy correction. We have also performed ultrahigh-resolution laser photoemission experiment on FeSe and observed the suppression of intensity around the Fermi level upon cooling., Comment: 6 pages, 3 figures

The energy gap of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu) was probed by angle resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet laser (photon energy 6.994 eV) or He I resonance line (21.218 eV) as photon source. The results show that the gap around the node at sufficiently low temperatures can be well described by a monotonic d-wave gap function for both samples and the gap of the R=La sample is larger reflecting the higher Tc. However, an abrupt deviation from the d-wave gap function and an opposite R dependence for the gap size were observed around the antinode, which represent a clear disentanglement between the antinodal pseudogap and the nodal superconducting gap., Comment: Submitted as the proceedings of LT25

The electronic structure near the Fermi level (E F ) of the β-pyrochlore superconductor KOs 2 O 6 is studied using laser-excited ultrahigh-resolution photoemission spectroscopy. The superconducting gap clearly opens across the superconducting transition (T c = 9.6 K), with the strong electron-phonon coupling value of 2Δ(0)/k B Τ c ≥ 4.56. A fitting analysis identifies clear anomalies at T P = 7.5 K in the temperature dependencies of the superconducting gap size and the quasiparticle relaxation lifetime. These anomalies and the fine spectral structures arising from phonons suggest that the existence of the rattling behavior of K ions significantly affects the superconductivity in KOs 2 O 6 .

The Nd-moment order in the layered nickelate Nd2−xSrxNiO4 (x = 0.7) has been investigated by performing a neutron diffraction experiment using a single crystal sample. First, the checkerboard (CB)-type charge order was confirmed by observing the temperature dependence of the nuclear superlattice peak at \(\boldsymbol{{Q}} = (5,0,0)\) between 1.9 and 300 K, which indicates that the transition temperature of the CB-type charge order is above 300 K. Magnetic superlattice peaks with the propagation vector \(\boldsymbol{{k}} = (1 - \varepsilon ,0,1)\) appear below 67 K, and the value of e was determined to be 0.455 in good agreement with previous studies. The intensity of the magnetic superlattice peaks appearing below 67 K shows a sharp increase below ≈20 K. This behavior indicates that the Nd moments freeze under the influence of the Ni ordering. The CB-type antiferromagnetic (AFM) Ni order in the NiO2 layers is stacked antiferromagnetically in the c-axis direction, while the Nd moments in the Nd/SrO2 layers...

The cobalt oxide superconductor Na(x)CoO(2) x yH(2)O is studied by angle-resolved photoemission spectroscopy. We report the Fermi surface (FS) topology and electronic structure near the Fermi level (E(F)) in the normal state of Na(x)CoO(2) x yH(2)O. Our result indicates the presence of the hexagonal FS centered at the Gamma point, while the small pocket FSs along Gamma-K direction are absent, similar to Na(x)CoO(2). The top of the e(g)(') band, which is expected in band calculations to form the small pocket FSs, extends to within approximately 30 meV below E(F), closer to E(F) than in Na(x)CoO(2). We discuss its possible role in superconductivity, comparing with other experimental and theoretical results.

We have performed a vacuum ultraviolet laser excited photoemission spectroscopy on a $d$-electron heavy-fermion-like material ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ single crystal. We observed a sharp peak structure in the density of states at $\ensuremath{\sim}4\text{ }\text{ }\mathrm{meV}$ above the Fermi level (${E}_{\mathrm{F}}$). The evolution of the peak height corresponds well with the crossover behavior to the heavy-fermion-like state as observed in the thermal and transport properties. The position, shape, and temperature ($T$) dependence of the peak structure is quite similar to the Kondo resonance observed in conventional $f$-electron heavy Fermion compounds.

We have investigated the low energy electronic state of a boron-doped diamond thin film by the ultrahigh resolution laser-excited photoemission spectroscopy. We observed a clear shift of the leading edge below 11 K indicative of a superconducting gap opening ($\Delta \sim 0.78$ meV at 4.5 K). The gap feature is significantly broad and the well-defined quasiparticle peak is not recognizable even at the lowest temperature of measurement 4.5 K. We discuss our result in terms of possible disorder effect on superconductivity in this system., Comment: 12 pages, 4 figures

The temperature (T) dependence of the charge-stripe order in La2-xSrxNiO4 has been investigated in the vicinity of x approximately 1/3 by synchrotron radiation x-ray diffraction measurements. With decreasing T, a prominent commensurate-incommensurate (C-IC) crossover is observed in the x 1/3 region the IC order is dominant over the whole T range. Such a C-IC crossover is interpreted as the entropy-driven self-doping of the charge stripes, and its x dependence indicates the clear electron-hole asymmetry with the x=1/3 compound as the Mott insulator.

We have investigated the temperature and doping variations of optical and transport properties in the electron-doped high-${T}_{\mathrm{c}}$ cuprate crystals ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ $(0l~xl~0.15).$ In the optical spectra of underdoped crystals $(xl0.15),$ a notable pseudogap is observed at low temperatures. A Drude-like response evolves concomitantly with pseudogap formation. Both the magnitude $({\ensuremath{\Delta}}_{\mathrm{PG}})$ and onset temperature ${(T}^{*})$ of the pseudogap decrease with electron doping, while holding the relation that ${\ensuremath{\Delta}}_{\mathrm{PG}}\ensuremath{\approx}{10k}_{\mathrm{B}}{T}^{*}.$ The ${\ensuremath{\Delta}}_{\mathrm{PG}}$ is comparable to the magnitude of the pseudogap at around $(\ensuremath{\pi}/2,\ensuremath{\pi}/2)$ in the photoemission spectra reported by Armitage et al. [Phys. Rev. Lett. 88, 257001 (2002)], which indicates that the pseudogap appearing in the optical spectra is identical to that discerned by the photoemission spectroscopy. The scattering rate spectra $1/\ensuremath{\tau}(\ensuremath{\omega})$ of the $x=0.10--0.15$ crystals show a kink structure at around 0.07 eV, which can be ascribed not to the pseudogap but to the electron-phonon coupling. In accordance with the evolution of the Drude response, the in-plane resistivity begins to decrease rapidly at around ${T}^{*}$ in the underdoped region. The out-of-plane resistivity shows an even more distinct decrease below ${T}^{*}.$ This is because the interplane charge transport is governed by electronic states at around $(\ensuremath{\pi},0),$ where the quasiparticle spectral weight is accumulated in the case of the electron-doped system. This is contrary to the hole-doped case with the pseudogap around this point. The origin of the pseudogap has been ascribed to the antiferromagnetic spin correlation, which is consistent with the evolution of a two-magnon band in the ${B}_{1\mathrm{g}}$ Raman spectra below ${T}^{*}.$ The pseudogap phenomenon in the electron-doped cuprate has been argued comparatively with that of the hole-doped cuprate.

The evolution of spin- and orbital-ordered states has been investigated for a series of insulating perovskites $R{\mathrm{MnO}}_{3}$ $(R=\mathrm{L}\mathrm{a},\mathrm{P}\mathrm{r},\mathrm{N}\mathrm{d},\dots{}).$ $R{\mathrm{MnO}}_{3}$ with a large ${\mathrm{GdFeO}}_{3}$-type distortion is regarded as a frustrated spin system having ferromagnetic nearest-neighbor and antiferromagnetic (AF) next-nearest-neighbor (NNN) interactions within a ${\mathrm{MnO}}_{2}$ plane. The staggered orbital order associated with the ${\mathrm{GdFeO}}_{3}$-type distortion induces the anisotropic NNN interaction, and yields unique sinusoidal and up-up-down-down AF ordered states in the distorted perovskites with ${e}_{g}^{1}$ configuration.

We have investigated the charge-spin-ordering transition in ${\mathrm{La}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{NiO}}_{4}$ by measurements of Raman and optical conductivity spectra. The checkerboard-type charge ordering below $\ensuremath{\sim}400\mathrm{K}$ can be probed by activated phonon ${(A}_{1g}$ and ${E}_{u})$ and two-magnon ${(B}_{1g})$ modes in the infrared and Raman spectra as well as by formation of pseudogaps in the optical conductivity spectra. Besides, another ${B}_{2g}$ Raman mode emerges below 150 K together with reduction of the optical gap, which can be attributed to another ordering process, i.e., the stripe formation.

A notable pseudogap ( ${\ensuremath{\Delta}}_{\mathrm{PG}}$ as large as 0.2--0.4 eV) has been found below a characteristic temperature ${T}^{*}$ in the optical conductivity spectrum for metallic but nonsuperconducting crystals of ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ $(xl0.15)$. The ${\ensuremath{\Delta}}_{\mathrm{PG}}$ and ${T}^{*}$ decrease with doping $x$, holding the relation of ${\ensuremath{\Delta}}_{\mathrm{PG}}\ensuremath{\approx}{10k}_{\mathrm{B}}{T}^{*}$. The Drude-like component is observed to evolve concomitantly with the pseudogap. The ${T}^{*}$ almost coincides with another characteristic temperature ${T}_{0}$ that scales the Hall coefficient. These results indicate that the charge transport in the underdoped region is under the strong influence of the pseudogap state.

In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E(B) = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation.

We have investigated temperature dependence of optical conductivity spectra comparatively for oxygenated (antiferromagnetic) and reduced (superconducting) crystals of Nd1.85Ce0.15CuO4+y. In the spectra of the oxygenated crystal, anomalous pseudogap structure, accompanied by phonon anomalies, evolves with decreasing temperature from 340 K, while these features almost disappear in the spectra of the reduced crystal. These anomalies are proposed to be due to charge ordering instability induced by a minute amount of interstitial apical-oxygen, which seems to suppress the superconductivity in the oxygenated (or as-grown) crystal.

We have investigated the electronic structures of antiferromagnetic superconductor ErNi 2 B 2 C by using laser-photoemission spectroscopy. The observed spectra below the superconducting transition temperature ( T c = 9.0 K) show a very broad coherent peak and finite density of states at the Fermi level due to strong magnetic pair breaking effects. In addition, we find a dip structure in the temperature dependence of the superconducting order parameter just below the antiferromagnetic ordering temperature ( T N = 6.0 K). This behavior can be well interpreted as a result of competition between the rapid evolution of the antiferromagnetic molecular field and the increase of the superconducting condensation energy with decreasing temperature.

We have observed the charge and the magnetic ordering in La2−xSrxNiO4(0.28⩽x⩽0.46) by neutron scattering. In the c-plane, holes and spins order as a two-dimensional system, where holes form stripes and they are inserted into the antiferromagnetic ordering. Along the c-axis, the two-dimensional ordering stacks. However, the coherence along the c-axis is much weaker than that in the c-plane. We discuss how two-dimensional ordering stacks and why the coherence along the c-axis becomes weak.

We report the results of first photoemission spectroscopy on a newly discovered noncentrosymmetric superconductor Mg 10 Ir 19 B 16 . We measured the valence band structure of Mg 10 Ir 19 B 16 using soft X-ray photoemission technique and found that the first principal calculation explains our observation well. In the bulk-sensitive laser-excited photoemission study, we observed that the intensity at the Fermi level decreases as we lower the sample temperature, indicative of the opening of superconducting energy gap. Using Dynes' function, we performed fitting analysis on the spectra of superconducting state.

Noncentrosymmetric superconductors Li 2 Pd 3 B and Li 2 Pt 3 B are studied by high-resolution photoemission spectroscopy. The valence band spectra of Li 2 Pd 3 B and Li 2 Pt 3 B are well explained by first-principles band calculations. The sub-meV photoemission result shows that the size of the superconducting gap of Li 2 Pd 3 B is about 1.1 meV at 5.4 K with a reduced gap value (2Δ 0 / k B T c ) of about 4.5, which is greater than the Bardeen–Cooper–Schrieffer (BCS) value of 3.52. The obtained superconducting gap can be explained more clearly with an s -wave superconducting gap than with p - and d -wave superconducting gaps. This result indicates that Li 2 Pd 3 B is a conventional strong-coupling superconductor.

We have developed a low temperature ultrahigh resolution system for polarization dependent angle-resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet (vuv) laser (hnu=6.994 eV) as a photon source. With the aim of addressing low energy physics, we show the system performance with angle-integrated PES at the highest energy resolution of 360 mueV and the lowest temperature of 2.9 K. We describe the importance of a multiple-thermal-shield design for achieving the low temperature, which allows a clear measurement of the superconducting gap of tantalum metal with a T(c)=4.5 K. The unique specifications and quality of the laser source (narrow linewidth of 260 mueV, high photon flux), combined with a half-wave plate, facilitates ultrahigh energy and momentum resolution polarization dependent ARPES. We demonstrate the use of s- and p-polarized laser-ARPESs in studying the superconducting gap on bilayer-split bands of a high T(c) cuprate. The unique features of the quasi-continuous-wave vuv laser and low temperature enables ultrahigh-energy and -momentum resolution studies of the spectral function of a solid with large escape depth. We hope the present work helps in defining polarization dependent laser excited angle-resolved photoemission spectroscopy as a frontier tool for the study of electronic structure and properties of materials at the sub-meV energy scale.