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We have investigated the electronic structure of silver chalcogenides Ag2X (X = S, Se, Te) and their solid solutions using hard x-ray photoemission spectroscopy in combination with density functional theory calculations using generalized gradient approximation (GGA). By including the corrections for on-site Coulomb interactions (GGA + U), we successfully reproduced the valence band photoemission spectra, which consist mainly of the Ag 4d band, by calculation. The estimated values for U = 4–6 eV are slightly high for Ag 4d electrons but are consistent with those used in previously reported structural studies. On the other hand, the magnitude of the energy gap is virtually independent of U. These results suggest the strong correlation between Ag 4d electrons in Ag2X compounds to have surprisingly little impact on their electron transport properties. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of a potential thermoelectric material, higher manganese silicide, and its solid solutions with supersaturated Re by means of hard x-ray photoemission spectroscopy. The unusual Re substitution dependence of thermoelectric properties in the higher manganese silicide, reducing the electrical resistivity without altering the Seebeck coefficient, can be explained in terms of the variation of the density of states at the Fermi level and its energy derivative. Such an electronic structure variation contributes to an improvement in the thermoelectric performance in combination with the suppressed thermal conductivity. [ABSTRACT FROM AUTHOR]

The dynamic interaction between the traveling charges and the molecular vibrations is critical for the charge transport in organic semiconductors. However, a direct evidence of the expected impact of the charge-phonon coupling on the band dispersion of organic semiconductors is yet to be provided. Here, we report on the electronic properties of rubrene single crystal as investigated by angle resolved ultraviolet photoelectron spectroscopy. A gap opening and kink-like features in the rubrene electronic band dispersion are observed. In particular, the latter results in a large enhancement of the hole effective mass (> 1.4), well above the limit of the theoretical estimations. The results are consistent with the expected modifications of the band structures in organic semiconductors as introduced by hole-phonon coupling effects and represent an important experimental step toward the understanding of the charge localization phenomena in organic materials. [ABSTRACT FROM AUTHOR]

We study the electronic structure of CeCuAs2, which is known to show an anomalous negative temperature coefficient of resistivity below room temperature, while the thermopower shows metallic behavior. We carry out hard x-ray photoemission spectroscopy (PES), x-ray absorption spectroscopy (XAS), and resonant PES across the Ce 3d-4f and Cu 2p-3d thresholds to investigate the role of Kondo screening in CeCuAs2. The Ce 3d core-level PES shows the f0, f1, and f2 features, and the Ce 3d-4f XAS shows corresponding features due to transitions into the f1 and f2 states, as in Kondo systems. The spectral feature assignments are confirmed by single-impurity Anderson model calculations and indicate a nearly trivalent-Ce configuration with small but finite mixed valency. The resonant PES valence band spectra across the Ce 3d-4f threshold show an intense Ce 4f1 resonance just below the Fermi level, while the Ce 4f0 feature is observed at a binding energy of 2.5 eV. The obtained f partial density of states shows an unusual pseudogaplike dip at the Fermi level in CeCuAs2. The results indicate the importance of Kondo screening and a pseudogap in the f partial density of states for the anomalous transport and magnetic properties of CeCuAs2. [ABSTRACT FROM AUTHOR]

The Kondo resonance at the Fermi level is well established for the electronic structure of Ce (4f¹ electron) and Yb (4f¹ hole)-based systems. In this work, we report complementary experimental and theoretical studies on the Kondo resonance in the Pr-based 4f² system, PrTi2Al20. Using Pr 3d-4f resonant photoemission spectroscopy and single-impurity Anderson model (SIAM) calculations including the full multiplets of Pr ions, we show that a 4f² system can also give rise to a Kondo resonance at the Fermi level. The Kondo resonance peak is experimentally observed through a final-state multiplet-dependent resonance and is reproduced with properly tuned hybridization strength in SIAM calculations. [ABSTRACT FROM AUTHOR]

Electronic structures of La2NiMnO6 epitaxial films are characterized using synchrotron-radiation photoelectron spectroscopy and optical spectroscopy. X-ray absorption spectra reveal that the valence states of Ni2+ and Mn4+ are dominant. The electronic structure at the valence band maximum is mainly derived from the Mn 3d state. The conduction band minimum is composed mostly of the Mn 3d-O 2p hybridized state. The optical gap is estimated to be about 1.5 eV based on the optical conductivity derived from optical spectra. [ABSTRACT FROM AUTHOR]

We study the electronic structure of Tsai-type cluster-based quasicrystalline approximants, Au64 Ge22 Yb14 (AGY-I), Au63.5 Ge20.5 Yb16 (AGY-II), and Zn85.4 Yb14.6 (Zn-Yb), by means of photoemission spectroscopy. In the valence band hard x-ray photoemission spectra of AGY-II and Zn-Yb, we separately observe a fully occupied Yb 4f state and a valence fluctuation derived Kondo resonance peak, reflecting two inequivalent Yb sites, a single Yb atom in the cluster center and its surrounding Yb icosahedron, respectively. The fully occupied 4f signal is absent in AGY-I containing no Yb atom in the cluster center. The results provide direct evidence for a heterogeneous valence state in AGY-II and Zn-Yb. [ABSTRACT FROM AUTHOR]

We report a comparative study of the electronic structure of the compounds LaTe and CeTe, both of which crystallize in the rock salt structure. LaTe is a paramagnetic metal while CeTe is known to exhibit anomalous Kondo-like transport behaviour and undergoes a transition to a complex magnetically ordered state at low temperature ( T N = 2.2 K). We carry out hard X-ray photoelectron spectroscopy (HAXPES) of the core-levels and valence band of LaTe and CeTe at T = 20 K, in order to characterize their intrinsic electronic structure, and to address the role of Kondo effect on the electronic structure of CeTe. The bulk sensitive core level HAXPES spectra show evidence of screened features in the La 3 d and Ce 3 d states mixed with plasmon features. From a careful analysis of the Te, La and Ce derived core levels, we separate out the respective origins of the satellites and show that CeTe indeed exhibits definitive but weak f 0 and f 2 satellites due to Kondo screening, in addition to the main f 1 peak. The comparison of the valence band spectra of CeTe obtained using HAXPES and soft X-ray PES clearly identifies the Ce 4 f derived features. Resonant photoelectron spectrosocopy across the Ce 3 d − 4 f threshold confirms the Ce 4 f 1 final state at the Fermi level, corresponding to the tail of the Kondo resonance feature which occurs above the Fermi level, while the Ce 4 f 0 final state feature is observed at a binding energy of 2.4 eV. The 4 f 0 and 4 f 1 final states show giant resonances compared to the off-resonant spectra. However, in contrast to typical Kondo systems, the tail of the Ce 4 f 1 Kondo resonance at the Fermi level is relatively suppressed compared to the Ce 4 f 0 feature, which exhibits an unusually strong resonance enhancement. The results are indicative of a weakened Kondo effect which favours the magnetically ordered ground state in CeTe. [ABSTRACT FROM AUTHOR]

We report on the electronic structure of the 111-type iron pnictide superconductor LiFeAs as a function of temperature using angle-resolved photoemission spectroscopy. Below approximately 50 K, both the dyz hole band at the Z point and the dxz/yz electron band at the A point shift to a higher binding energy side. However, at the high-symmetry points Z, A, T, and M, the remaining bands are almost independent of temperature. One of the possible scenarios for these observations is that a strong, three-dimensional orbital-dependent correlation exists in the normal state of LiFeAs in relation to short-range spin fluctuations. [ABSTRACT FROM AUTHOR]

We study the electronic structure of bulk single crystals and epitaxial films of Fe3O4. Fe 2p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model--and in contrast to an earlier peak assignment--we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above TV and its T-dependent evolution. The Fe 2p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at EF for the polaronic half metal with a remnant order above TV and a clear gap formation below TV. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active fl-site electronic states, consistent with resistivity and optical spectra. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of Fe2P(0001) has been investigated by photoelectron spectroscopy (PES) utilizing synchrotron radiation. In the valence band (VB) spectra, an Fe 3d–P 3p hybrid band (main band) was observed at 0–3eV independent of photon energy, and satellites were observed at 4.5 and 7eV at hν <55eV. The satellites showed a resonant behavior around the Fe 3p threshold, and are associated with the photoemission process leading to two-hole bound final states. The slight Ar+ ion sputtering (1kV, 5min) induced little change in VB spectra, while core-level PES study showed that the P atoms in the surface region were selectively removed. This suggests that the stabilization of the metal sites due to the bonding with P atoms is ineffective on Fe2P(0001), unlike the situation reported earlier for Ni2P. [Copyright &y& Elsevier]

The electronic structure of a quantum spin liquid compound, EtMe3Sb[Pd(dmit)2]2, has been studied with angle-resolved photoemission spectroscopy, together with two other Pd(dmit)2 salts in the valence bond solid or antiferromagnetic state. EtMe3Sb[Pd(dmit)2]2, being a Mott insulator, has its lower Hubbard band identified, with a soft energy gap at the chemical potential. In addition, the spectral features exhibit anomalously broad linewidth and negligible dispersion, which fit well to the calculated energy levels of an isolated [Pd(dmit)2]2 dimer. We suggest that these electronic characteristics might be the manifestation of the spin-charge separation in a two-dimensional quantum spin liquid. [ABSTRACT FROM AUTHOR]

We report angle-resolved photoemission spectroscopy results of A-site ordered perovskite CaCu3Ti4O12. We have observed the clear band dispersions, which are shifted to the higher energy by 1.7 eV and show the band narrowing around 2 eV in comparison with the local density approximation calculations. In addition, the high-energy multiplet structures of Cu 3d8 final states have been found around 8-13 eV. These results reveal that CaCu3Ti4O12 is a Mott-type insulator caused by the strong correlation effects of the Cu 3d electrons well hybridized with O 2p states. Unexpectedly, there exists a very small spectral weight at the Fermi level in the insulator phase, indicating the existence of isolated metallic states. [ABSTRACT FROM AUTHOR]

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 1T-TaS2, realized by developing a high-intensity 60-eV laser obtained by high-order harmonic generation. Ta4f 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. [ABSTRACT FROM AUTHOR]