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We study epitaxial NdNiO3 thin films on NdGaO3(001) single-crystal substrates grown using a pulsed-laser deposition method. The films show a clear first-order metal-insulator transition (MIT) at TMI∼240 K, which is significantly higher than TMI∼190 K in bulk NdNiO3. The x-ray reciprocal space map shows in-plane tensile and out-of-plane compressive strain, stabilizing the more distorted NdNiO3 thin films with the higher transition temperature. Hard x-ray photoemission shows changes across the MIT and the bandwidth-controlled charge-transfer gap opens due to the reduced p-d hybridization in the low-temperature insulating phase. [ABSTRACT FROM AUTHOR]

We have examined the valence-band electronic structures of gold and silver in the same column in the periodic table with nominally filled d orbitals by means of a recently developed polarization-dependent hard x-ray photoemission. Contrary to common expectation, it is found that the 5dorbital electrons contribute prominently to the conduction electrons in gold, while the conduction electrons in silver are to some extent free-electron-like with negligible 4d contribution, which could be related to the well-known fact that gold is more stable than silver in air. The 4d electron correlation effects are found to be essential for the conduction electron character in silver. [ABSTRACT FROM AUTHOR]

Hard and soft x-ray photoelectron spectroscopies (called HAXPES and SXPES) were performed at ~8 and ~1.25 keV for the metal-insulator transitions (MIT) system VO2. From the sharp difference between HAXPES and SXPES in the O 1s spectra, it was found that the clean surface of the metal VO2 is covered with a less itinerant surface layer. Clear changes of the spectral shapes were observed in HAXPES on MIT for the V 1s, 2p, 3s, 3p and O 1s core levels. The enhanced intensity of these core levels in the low-binding-energy (EB) region of the main peak in the metal phase is due to the non-local or long range screening effects. The V 3d valence band in the metal phase is composed of coherent and incoherent parts. The prominent peak near 0.9 eV in the insulator phase has an incoherent tail in the high-EB region and the peak and its lower EB components are understood to have a noticeable coherent component. It is experimentally confirmed that both electron correlation and band changes induced by lattice distortion are responsible for the spectral changes on MIT in VO2. [ABSTRACT FROM AUTHOR]

Hard and soft x-ray photoelectron spectroscopy was performed for core and valence electrons in solid compounds containing V and O atoms. The single-nucleus recoil effects on photoelectron emission were observed in the form of recoil shifts for all core levels and the valence band in a heavy Fermion material LiV2O4, whereas such shifts were negligible in VO2 even in the high temperature metal phase. The valence band recoil shifts of V5O9 and V2O3 metal are found to be in between. These differences in the valence band are ascribable to the difference in the relative spectral weight of the O 2p component near the Fermi level. [ABSTRACT FROM AUTHOR]

Hard x-ray valence band photoemission spectroscopy (PES) is realized using high-energy and high-brilliance synchrotron radiation. High-energy (∼6 keV) excitation results in larger probing depths of photoelectrons compared to conventional PES, and enables a study of intrinsic electronic property of materials in actual device structures much less influenced by surface condition. With this technique, requirements for surface preparation are greatly reduced, if not eliminated. It is a nondestructive tool to determine electronic structure from surface to genuine bulk as shown by a study on SiO2/Si(100). Electronic structure modification related to the ferromagnetism in the diluted magnetic semiconductor Ga0.96Mn0.04N is also observed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have revealed that anisotropic 4f charge distributions caused by the crystalline electric field are responsible for linear dichroism (LD) in 3d core-level photoemission spectra of rare earth compounds. Indeed, we have successfully observed the intrinsic LD for cubic YbB 12 and tetragonal SmCu 2 Si 2 . We have also performed polarization-dependent 4f photoemission in a valence-band region. The observed LDs in the experimental 4f spectra are reduced from those predicted from the theoretical simulations for the localized ions. [ABSTRACT FROM AUTHOR]

We present genuine bulk Ir 5d jeff states of layered perovskite iridates obtained by hard-x-ray photoemission spectroscopy (HAXPES) with s- and p-polarized lights. HAXPES spectra of Sr2IrO4 and Ba2IrO4 are well reproduced by the quasiparticle density of states calculated by the local density approximation with dynamical mean-field theory (LDA+DMFT). It is demonstrated that the insulating nature of the iridates is triggered by antiferromagnetic correlation (Slater type) combined with electron correlation (Mott type). The extremely-low-energy bulk-sensitive photoemission spectroscopy reveals "bad metallic" states in the paramagnetic phase of the iridates, suggesting strongly renormalized metallic states above the Néel temperature as predicted by the LDA+DMFT. [ABSTRACT FROM AUTHOR]

We have performed high-resolution hard-x-ray photoemission spectroscopy for the metal-insulator transition (MIT) system (V1-xCrx)2O3 in the paramagnetic metal, paramagnetic insulator, and antiferromagnetic insulator phases. The quality of the spectra enables us to conclude that the on-site Coulomb energy U does not change through the MIT, which eliminates all but one theoretical MIT scenario in this paradigm material. [ABSTRACT FROM AUTHOR]

Hard and soft x-ray photoelectron spectroscopies (called HAXPES and SXPES) were performed at ~8 and ~1.25 keV for the metal-insulator transitions (MIT) system VO2. From the sharp difference between HAXPES and SXPES in the O 1s spectra, it was found that the clean surface of the metal VO2 is covered with a less itinerant surface layer. Clear changes of the spectral shapes were observed in HAXPES on MIT for the V 1s, 2p, 3s, 3p and O 1s core levels. The enhanced intensity of these core levels in the low-binding-energy (EB) region of the main peak in the metal phase is due to the non-local or long range screening effects. The V 3d valence band in the metal phase is composed of coherent and incoherent parts. The prominent peak near 0.9 eV in the insulator phase has an incoherent tail in the high-EB region and the peak and its lower EB components are understood to have a noticeable coherent component. It is experimentally confirmed that both electron correlation and band changes induced by lattice distortion are responsible for the spectral changes on MIT in VO2. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the electronic structure of configuration vanadium oxides (VO2, SrVO3 and CaVO3) using soft X-ray (SX) and hard X-ray (HX) photoemission spectroscopy (PES). The valence band spectra of VO2 in SX- and HX-PES clearly show the opening of a gap at across the metal–insulator transition. Spectral changes in the V 2p and O 1s core levels were also observed. In addition, configuration correlated metals SrVO3 and CaVO3 are typical materials whose valence band spectra are compared with dynamical mean-field theory. The V 2p and V 1s core level HX-PES of SrVO3 and CaVO3 show clear additional well-screened features. These features originate from bulk screening by a coherent band at . These spectra are nicely reproduced by a cluster model calculation, indicating a difference of the parameter for the interaction strength between the central V 3d orbitals and the coherent band. [Copyright &y& Elsevier]

Abstract: We have measured Ir 4f core-level photoemission spectra using an excitation photon energy of for single crystalline at 250 and across the metal–insulator transition temperature of about . The Ir 4f spin–orbit doublet shifts by about towards higher binding energy with decreasing temperature. Tails and satellites around 1 and , respectively, higher in binding energy than the peaks of Ir 4f doublets are observed in the 250-K spectrum, but they almost disappear at . The peak analysis here done indicates that the Ir 4f spectrum at consists of two components apart corresponding to the charge separation of Ir ions in . [Copyright &y& Elsevier]

Here we report investigation of valence band electronic states of ferromagnetic Ga0.96Mn0.04N by bulk-sensitive X-ray photoemission, which is realized at high flux X-ray undulator beamline BL29XU of SPring-8, at photon energy of 5.95 keV. We have observed that Mn doping introduces a new structure in the band gap region near the top of the valence band, and also a broader structure in deeper valence band region. Basing upon the first principle calculation, these structures are assigned as Ga 4s originated states, which are raised by hybridization between 3d orbitals of Mn with GaN host orbitals. The present result evidences the second nearest Ga bonds are affected by that Mn–N bond formation, suggesting the long-range interaction of Mn in this host material. [Copyright &y& Elsevier]

Abstract: We have carried out soft and hard X-ray spectroscopy of Sm-based filled skutterudites SmFe4 P12 and SmOs4 Sb12. Sm 3d–4f resonant photoemission and Sm 3d–4f X-ray absorption spectra suggest that SmOs4 Sb12 has much more strongly mixed Sm valence state than SmFe4 P12 in the bulk. On the other hand, the Sm trivalent state is dominant on the surface of SmOs4 Sb12. [Copyright &y& Elsevier]

• Linear dichroism (LD) in Pr3+ 3 d 5/2 core-level photoemission spectra has been observed for cubic PrB 6 , PrIr 2 Zn 20 and PrBe 13. • The experimental LDs and polarization-dependent spectra are well reproduced by ionic-model calculations taking the crystalline electric fields into account. • The 4 f ground-state symmetry of cubic Pr compounds can be determined by linearly polarized Pr 3 d core-level photoemission spectroscopy. We report the core-level photoemission study of cubic PrBe 13 , PrIr 2 Zn 20 and PrB 6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3 d core-level photoemission spectra reflecting the 4 f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3 d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4 f ground-state symmetry. [ABSTRACT FROM AUTHOR]

Abstract: We have carried out hard X-ray photoemission spectroscopy (HXPES) for pyrochlore molybdenum oxides Sm2Mo2O7 and Tb2Mo2O7 single crystals with excitation energy of 5.95keV, in order to investigate electronic structures and correlations in the bulk. The Mo 3d core spectra show complex features, in contrast to an ordinary doublet spectral feature derived from the spin–orbit interaction, indicating significant electron correlation in the valence band. While an intense peak structure at ∼0.5eV is observed in the valence band of Sm2Mo2O7, the peak is broadened and shifted way in Tb2Mo2O7, which suggests the difference of the electron correlation energy depending on the rare-earth site. [Copyright &y& Elsevier]

Abstract: We have realized hard X-ray (HX) photoemission spectroscopy (PES) with high throughput and high-energy resolution for core level and valence band studies using high-energy and high-brilliance synchrotron radiation at SPring-8. This is a brand new method because large escape depth of high-energy photoelectrons enables us to probe intrinsic bulk states free from surface condition. By use of a newly developed electron energy analyzer and well-focused X-rays, high-energy resolution of 75meV (E/ΔE =79,000) was realized for 5.95keV photoelectrons. [Copyright &y& Elsevier]

Yb 3d and valence-band photoemission spectra of YbInCu4 have been measured at hν=5.95 keV. Abrupt changes are observed in both spectra, reflecting the valence transition at Tν=42 K. The Yb valence estimated from the Yb 3d spectra is z∼2.90 at 220–50 K and sharply decreases to z∼2.74 at 30–10 K. [Copyright &y& Elsevier]

Abstract: Sm-based filled skutterudites and have been investigated by soft and hard X-ray photoemission spectroscopy (PES). Bulk-sensitive Sm 3d–4f resonant PES and surface-sensitive valence-band PES spectra suggest in the bulk that has much more strongly mixed Sm valence state than . A significant Sm divalent peak in the vicinity of the Fermi level () has been observed in , indicating that the Sm 4f states contribute to the electronic states at . [Copyright &y& Elsevier]

Abstract: We study the electronic structure of Mott–Hubbard systems SrVO and CaVO with photoemission spectroscopy (PES) using hard X-rays (HX) ( 8keV) and soft X-rays (SX) ( 900eV). In HX-PES results, the V 2p core levels of SrVO and CaVO show clear additional intensity, which are not observed in SX-PES. These features originate from bulk screening by coherent states at Fermi level as observed in other 3d transition metal oxides. From the comparison between SrVO and CaVO in HX-PES, the intensity in SrVO is nearly similar to CaVO. The results suggest screening from coherent states is more efficient in HX-PES compared to SX-PES. [Copyright &y& Elsevier]

Abstract: We have examined the electronic states of the Kondo semiconductor CeRhAs and the semimetal CeRhSb by means of high-resolution photoemission spectroscopy using tunable photon energies from up to 5948eV. On the basis of the photon-energy dependence of the photoionization cross-section, we have elucidated the p–d–f hybridized states in these compounds. [Copyright &y& Elsevier]