Mahmoud Khaled Abusamak

The electronic structure of the new superconducting material LaNiPO experimentally probed by soft X-ray spectroscopy and theoretically calculated by the combination of local density approximation with Dynamical Mean-Field Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray emission (XES) and absorption (XAS) spectra which probe the occupied and unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are strongly renormalized by dynamical correlations and shifted about 1.5 eV lower in the valence band than the corresponding Fe 3d states in LaFeAsO. We further obtain a lower Hubbard band at –9 eV below the Fermi level in LaNiPO which bears striking resemblance to the lower Hubbard band in the correlated oxide NiO, while no such band is observed in LaFeAsO. These results are also supported by the intensity ratio between the transition metal L2 and L3 bands measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the presence of the stronger electron correlations in the Ni 3d states in LaNiPO in comparison with the Fe 3d states in LaFeAsO. These findings are in accordance with resonantly excited transition metal L3 X-ray emission spectra which probe occupied metal 3d-states and show the appearance of the lower Hubbard band in LaNiPO and NiO and its absence in LaFeAsO.

Electrical properties and optical band gap of amorphous Se65Ga30In5 thin films, which were thermally evaporated onto chemically cleaned glass substrates, have been studied before and after thermal annealing at temperatures above the glass transition temperature and below the crystallization temperature. The IeV characteristics, which were recorded in the temperature range (200e300 K), were obtained at different voltages and exhibit an ohmic and non-ohmic behavior at low (0e5 V) and high (5 e18 V) voltages, respectively, for annealed and as-prepared films. Analysis of the experimental data in the high voltage range confirms the presence of space charge limited conduction (SCLC) for annealed and as-prepared films. The dependence of DC conductivity on temperature in the low voltage region shows two types of conduction channels: The first is in the range 270e300 K and the other at the lower temperature range (200e270 K). The conduction in the first region is due to thermally activated process, while in the other is due variable range hopping (VRH) of charge carriers in the band tails of the localized states. After annealing, the conductivity has been found to increase but the activation energy decreases. This is attributed to rupturing of SeeIn weak bonds and formation of SeeGa strong bonds. This process changes the concentration of defects in the films which in turn decreases the density of states N(EF) as predicted by Mott’s VRH model. Analysis of the absorption coefficient of annealed and as-prepared films, in thewavelength range 300e700 nm, reveals the presence of parabolic densities of states atthe edges of both valence and conduction bands in the studied films. The optical band gap (Eg) was obtained through the use of Tauc’s relation and is found to decrease with annealing temperature

This paper reports on the band structure properties and changes in band structure of fluorine-doped LaO1−xFxFeAs (x = 0, 0.2) compound, measured using X-ray photoemission spectroscopy (XPS). The band structure of the superconducting compound is compared with nonsuperconducting parent compound LaOFeAs. With fluorine doping, a shift of the shallow core level is observed in XPS spectra, which may be a response of the band structure due to fluorine doping in the system. The balance of the chemical potential shift with the screening effect of conduction electrons near the Fe and As ions is discussed using nearly unchanged Fe 2p and As 3d core-level spectra. The La 3d core-level spectra shift towards the high energy, ∼0.36eV, may bedue tothe chemical potential shift caused by fluorine doping. In our valence band spectra, a small peak at around 0.2 eV is observed, which disappeared with the fluorine doping in the system, indicating a change of Fe 3d state from low spin to high spin states and also confirming the nature of Fe 3d electrons as itinerant, which is responsible for superconductivity in these compounds.

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precursors

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precurso

The electronic structure of the new superconducting material LaNiPO experimentally probed by soft X-ray spectroscopy and theoretically calculated by the combination of local density approximation with Dynamical Mean-Field Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray emission (XES) and absorption (XAS) spectra which probe the occupied and unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are strongly renormalized by dynamical correlations and shifted about 1.5 eV lower in the valence band than the corresponding Fe 3d states in LaFeAsO. We further obtain a lower Hubbard band at –9 eV below the Fermi level in LaNiPO which bears striking resemblance to the lower Hubbard band in the correlated oxide NiO, while no such band is observed in LaFeAsO. These results are also supported by the intensity ratio between the transition metal L2 and L3 bands measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the presence of the stronger electron correlations in the Ni 3d states in LaNiPO in comparison with the Fe 3d states in LaFeAsO. These findings are in accordance with resonantly excited transition metal L3 X-ray emission spectra which probe occupied metal 3d-states and show the appearance of the lower Hubbard band in LaNiPO and NiO and its absence in LaFeAsO.

Electrical properties and optical band gap of amorphous Se65Ga30In5 thin films, which were thermally evaporated onto chemically cleaned glass substrates, have been studied before and after thermal annealing at temperatures above the glass transition temperature and below the crystallization temperature. The IeV characteristics, which were recorded in the temperature range (200e300 K), were obtained at different voltages and exhibit an ohmic and non-ohmic behavior at low (0e5 V) and high (5 e18 V) voltages, respectively, for annealed and as-prepared films. Analysis of the experimental data in the high voltage range confirms the presence of space charge limited conduction (SCLC) for annealed and as-prepared films. The dependence of DC conductivity on temperature in the low voltage region shows two types of conduction channels: The first is in the range 270e300 K and the other at the lower temperature range (200e270 K). The conduction in the first region is due to thermally activated process, while in the other is due variable range hopping (VRH) of charge carriers in the band tails of the localized states. After annealing, the conductivity has been found to increase but the activation energy decreases. This is attributed to rupturing of SeeIn weak bonds and formation of SeeGa strong bonds. This process changes the concentration of defects in the films which in turn decreases the density of states N(EF) as predicted by Mott’s VRH model. Analysis of the absorption coefficient of annealed and as-prepared films, in thewavelength range 300e700 nm, reveals the presence of parabolic densities of states atthe edges of both valence and conduction bands in the studied films. The optical band gap (Eg) was obtained through the use of Tauc’s relation and is found to decrease with annealing temperature

This paper reports on the band structure properties and changes in band structure of fluorine-doped LaO1−xFxFeAs (x = 0, 0.2) compound, measured using X-ray photoemission spectroscopy (XPS). The band structure of the superconducting compound is compared with nonsuperconducting parent compound LaOFeAs. With fluorine doping, a shift of the shallow core level is observed in XPS spectra, which may be a response of the band structure due to fluorine doping in the system. The balance of the chemical potential shift with the screening effect of conduction electrons near the Fe and As ions is discussed using nearly unchanged Fe 2p and As 3d core-level spectra. The La 3d core-level spectra shift towards the high energy, ∼0.36eV, may bedue tothe chemical potential shift caused by fluorine doping. In our valence band spectra, a small peak at around 0.2 eV is observed, which disappeared with the fluorine doping in the system, indicating a change of Fe 3d state from low spin to high spin states and also confirming the nature of Fe 3d electrons as itinerant, which is responsible for superconductivity in these compounds.

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precursors

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precurso