1,720,964 research outputs found
Correlation effects on the electronic properties of Bi2Sr2CaCu2O8
No full textWe have studied the role of on-site electronic correlation on the band structure of Bi2Sr2CaCu2O8. In our approach, an ab initio calculation supplies for the single particle starting point, on top of which self-energy effects are explicitly taken into account in the framework of the three-body scattering theory (3BS). We observe that correlation modifies the energy dispersion of hole quasiparticle states near the Fermi level, especially close to the X and (M) over bar symmetry points, but does not induce sensible changes at the Fermi level. To sustain this picture, we report calculations of effective masses
Theoretical simulation of core-level photoemission in transition-metal oxides
No full textWe discuss the 2p and 3s line shape in NiO and MnO photoemission, and we show that the main features of all the spectra for both systems are reproduced within an unique theoretical scheme that takes into account the dynamics of the created photohole, together with the detailed band structure of the compounds. The solid state bonding and the antiferromagnetic order are found to deeply influence the characteristics of core level spectra; in particular, the large difference in the spin unbalance of MnO and NiO explains the different response of the two compounds to the creation of a core hole
Spin dependent many-body effects in the photoemission of Co
No full textMany-body effects influence the energy versus momentum relation that is measured in angle-resolved photoemission experiments and the quasi-particle band structure may be significantly different from what is deduced within the independent particle model. In the case of cobalt many body effects are even more drastic than an energy renormalization giving rise to a quenching of quasi-particle peaks. Augmenting ab-initio band structure with many-body e-e interactions, we have obtained spin- and k-dependent self-energies, hole spectral functions and quasi-particle energies to be compared with photoemission spectra; our results show that e-e correlations are responsible for strong spin-dependent energy renormalizations
Band-structure effects in the core-level photoemission spectra of NiO
No full textCalculation of Ni 2p photoelectron spectra for NiO has been performed within a picture which takes into full account the itinerant character of valence electrons and the localized many-body interaction between core and valence electrons. The results of an nb initio band-structure calculation are used as an input for the calculation of self-energy correction and spectral function according to a three-body scattering solution of a many-body Hamiltonian which includes the Coulomb repulsion between core and valence states. The calculated spectrum shows, in agreement with experimental data, a doubly peaked main line which can be attributed to two independent relaxation processes involving valence-baud Ni d states of either pure or hybridized orbital character
ARPES band maps of ferromagnetic iron: Theoretical simulation including e-e correlation
No full textMany-body effects influence the energy-versus-momentum relation that is measured in angle resolvedphotoemission experiments and the quasiparticle band structure may be significantly differentfrom what is deduced within the independent particle model. Stimulated by recent high resolutionphotoemission data for iron showing quasiparticle renormalization close to the Fermi energy [1] wehave performed a systematic study 3d transition metals including on-site e-e correlation within the3Bs approach [2]; this amounts to solve a multi-orbital Hubbard Hamiltonian through an expansionof the interacting state in terms of configurations with one electron-hole pair added to the non interactingground state. The systematic analysis of metals of the 3d transition series allow us to showthat band occupation is a key parameter to quantify the effectiveness of many-body interactions. Wefind that e-e correlations are responsible for spin-dependent energy renormalization; in iron it turnsout that empty minority spin states are most affected while the same is true for filled majority spinones. A detailed analysis of energy dispersion curves after the inclusion of many body correctionand a comparison with measured spectra is also shown
Ab Initio Simulation of Optical Limiting: The Case of Metal-Free Phthalocyanine
Full text linkWe present a fully ab initio, nonperturbative description of the optical limiting properties of a metal-free phthalocyanine by simulating the effects of a broadband electric field of increasing intensity. The results confirm reverse saturable absorption as the leading mechanism for optical limiting phenomena in this system and reveal that a number of dipole-forbidden excitations are populated by excited-state absorption at more intense external fields. The excellent agreement with the experimental data supports our approach as a powerful tool to predict optical limiting in view of applications
Ab initio Fermi surface and conduction-band calculations in oxygen-reduced MoO3
No full textThis article reports ab initio Fermi surfaces and conduction-band calculations of both stoichiometric and oxygen-reduced MoO3. The data, based on a TB-LMTO approach in LDA, provide a convincing and detailed interpretation of the one-electron removal XPS valence bands, where a clear energy gap is observed for the stoichiometric samples, whereas a significant emission at the Fermi edge is measured for the oxygen reduced system. In addition, the electrical conductivity, as deduced from the shape of the calculated Fermi surface, is confined in the xz plane of the crystal, as required for Luttinger-liquid behavior. These results, when compared to the conduction mechanism observed in the blue bronze K0.3MoO3, clearly suggest that oxygen reduction and doping can bring to very different processes for the electronic transport
Quenching of majority-channel quasiparticle excitations in cobalt
No full textThe low-energy electronic excitations in cobalt are studied by a theoretical method that includes many-body effects and a realistic description of the band structure. Angle-resolved photoemission spectra measured on a thick film of hexagonal close-packed Co on Cu(111) agree well with calculated spectral functions. Because of many-body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV and in this energy region the spectrum is essentially incoherent. The many-body corrections are much stronger in the majority-spin channel and drastically affect the spin polarization of the spectra
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