Electronic structure of NiO and related 3d-transition-metal compounds

The electronic structure of the transition-metal compounds is discussed with nickel oxide (NiO) serving as the prime example. Other systems are also discussed, especially the high-temperature superconductors. The main finding of the review from the inspection of many data is that the electronic structure of these compounds is severely influenced by correlation of the Mott-Hubbard-type. Also in the metallic (itinerant) state these systems show aspects of correlations (satellites), which can only be explained in a one-ion model. It is this simultaneous occurrence of one-ion and one-electron features which makes the investigation of this class of materials fascinating but also frustrating, because at this point there is no unified theoretical approach available that would allow one to describe the electronic properties of these systems coherently.     

Splitting of core-level lines in photoemission spectra of transition metal compounds

The multiplet structure of core-electron binding energies in Cr 3s, Cr 3p and Cr 2p levels of CrCl₃ and CrBr₃ compounds has been investigated by X-ray photoelectron spectroscopy. The Cr 3s levels show a doublet splitting (about 4.3?eV) for the main emission in both halides. Satellites features are observed in Cr 3s, 3p and 2p levels at higher binding energies. In the Cr 3s spectrum, the main emission is assigned to unscreened intra-atomic multiplet splittings with correlation-induced satellites. The Cr 3p and 2p spectra can be better explained by the multiplet splitting arising from the interaction between valence band 3d electrons and core p holes in the crystal field. Final state screening (charge-transfer) effects do not play a major role in Cr 3s main emission nor do they affect the satellite structures in a relevant way. This explains why the Cr 3s exchange splitting in chromium halides is proportional to the local magnetic moment.     

Effects of configuration-dependent hybridization on core-level photoemission spectra

The Ni2p X-ray photoemission spectrum (XPS) for NiCl₂ is reanalyzed on the basis of a NiCl₆⁴⁻ cluster model. By taking into account the electron configuration dependence of the hybridization strengths between Ni3d and Cl3p orbitals, we show that the model can consistently reproduce the experimental 2p-XPS and the energy gap of the system.     

Revisiting the valence-band and core-level photoemission spectra of NiO

We have reexamined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopies. The spectral weight of the lowest energy state was found to be enhanced in the bulk sensitive Ni 2p core-level spectrum. A configuration-interaction model including a bound state screening has shown agreement with the core-level spectrum and off- and on-resonance VB spectra. These results identify the lowest energy states in the core-level and VB spectra as the Zhang-Rice (ZR) doublet bound states, consistent with the spin-fermion model and recent ab initio calculations within dynamical mean-field theory. The results indicate that the ZR character first ionization (the lowest hole-addition) states are responsible for transport properties in NiO and doped NiO.     

Electronic structure of layered uranium compounds from photoemission spectroscopy

We present the photoemission results of two layered tetragonal compounds, the anti-ferromagnet UAsSe and ferromagnet USb₂. We observed intriguing electronic structure for both UAsSe and USb₂, in which relatively dispersive and narrow 5f bands are present. In the vicinity of the Fermi edge we found a very sharp photoemission peak with dispersion of several meV along the Γ to Z direction of the Brillouin zone. We also found a broader, hybridized f-character band with dispersion of several hundred meV along the Γ to X direction. Narrow and dispersive bands in these U-based magnetic materials are reminiscent of band magnetism as previously found in some transition metals.     

Electronic structure and photoemission on VNi3

The electronic structure of VNi₃ has been calculated and compared with the experimental results from photoemission, magnetic susceptibility and heat capacity measurements. The linearized muffintin orbitals method is used to compute the electronic density of states. Both paramagnetic and spin-polarized calculations have been performed and give results in good overall agreement with the experimental data.     

Valence band and core-level photoemission spectra of black phosphorus single crystals

Valence band structures of black phosphorus have been measured by synchrotron-radiation photoemission spectroscopy. The excitation photon-energy dependence of the spectra has provided information about the 3s-3p hybridization. As for inner core-levels, binding energies of 2p and 2s core-levels, $\text{2p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ splitting, and the bulk plasmon energy are estimated from X-ray photoemission spectroscopy.     

Electronic structure and calculated x-ray photoemission spectra of substoichiometric cubic molybdenum nitride

Total and partial densities of states of substoichiometric cubic MoN _x have been calculated for several concentrationsx by means of the KKR-CPA method. There are significant differences to the results of Papaconstantopoulos and Pickett [1] obtained by the LCAO-CPA method. In particular, the concentration dependence of the DOS at the Fermi energy is quite different. Using the single-scatterer final-state approximation, Al–K-XPS spectra have been calculated. It is found that the first peak in the valence band spectra is due mainly to metal-p rather than nonmetal-p states. The vacancy states in the DOS of substoichiometric MoN _x give also rise to an additional peak in the XPS spectra.     

Nature of the well screened state in hard X-ray Mn 2p core-level photoemission measurements of La1-xSrxMnO3 films

Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison of Mn 2p core-levels with soft x-ray (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping-induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX PES.     

Electronic structure analysis of Mn- and Fe-codoped In2O3 by photoemission yield measurements

The valence band electronic structures of Mn- and/or Fe-doped In₂O₃, i.e., In₂O₃:Mn, In₂O₃:Fe, and In₂O₃:(Mn, Fe), are investigated by photoemission yield measurements. Significant changes are observed in the threshold energy of photoemission, depending on the doped magnetic ions, which indicates that an additional occupied band appears above the top of the valence band of In₂O₃ owing to doping with Mn and/or Fe ions. It is confirmed that the order of the threshold energies of photoemission, E_PET, is E_PET(In₂O₃:Mn)<E_PET(In₂O₃:(Mn, Fe))<E_PET(In₂O₃:Fe)<E_PET(In₂O₃). To gain a better understanding of these results, first-principles molecular orbital calculations are also carried out, which successfully explain the observed changes in the photoemission threshold energies.     

Electronic structure of MgB2 from angle-resolved photoemission spectroscopy

The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching the Fermi energy. These can be assigned to the theoretically predicted sigma (B 2p(x,y)) and pi (B 2p(z)) bands. In addition, a small parabolic-like band is detected around the Gamma point, which can be attributed to a surface-derived state. The overall agreement between our results and the band calculations suggests that the electronic structure of MgB2 is of a conventional nature, thus implying that electron correlations are weak and may be of little importance to superconductivity in this system.     

Electronic structure of the YH3 phase from angle-resolved photoemission spectroscopy

Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We report on angle-resolved photoemission experiments of the Y trihydride phase. Most importantly, we find the absence of metal d bands at the Fermi level and a set of flat, H-induced bands located at much higher binding energy than predicted, indicating an increased electron affinity at H sites.     

Study on the electronic structure and Fermi surface of 3d-transition-metal disilisides CoSi2

We have investigated the electronic structure, the momentum density distribution ρ(p), and the Fermi surface FS of single crystals of the Pyrite-type 3d-transition-metal disilisides CoSi₂. The band structure calculations, the density of states DOS, and the FS, in vicinity of Fermi level, have been carried out using the full-potential linearized augmented plane wave FP-LAPW method within generalized gradient approximation GGA for exchange and correlation potential. The measurements have been performed via the 2D angular correlation of annihilation radiation ACAR experiments. ρ(p) has been reconstructed by using the Fourier transformation technique. The FS has been reconstructed within the first Brillion zone BZ through the Locks, Crisp, and West LCW folding procedures. The analysis confirmed that Si 3sp states hybrid with both Co 3d–t _2g and Co 3d–e _g states around Γ and X points, respectively. The dimensions of the FS of CoSi₂ have been compared to the present calculations as well as to the earlier results.