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Register a new userElectronic structure of Pr2MnNiO6 from x-ray photoemission, absorption and density functional theory
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Added by
Padmanabhan Balasubramanian Dr
Publication date
2017
fields
Physics
and research's language is
English
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The electronic structure of double perovskite Pr2MnNiO6 is studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 2+ and 4+ states respectively. Using charge transfer multiplet analysis of Ni and Mn 2p XPS spectra, we find charge transfer energies {Delta} of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the atomic values of 8.00 and 3.00 respectively thereby indicating the covalent nature of the system. The O 1s edge absorption spectra reveal a band gap of 0.9 eV which is comparable to the value obtained from first principle calculations for U-J >= 2 eV. The density of states clearly reveal a strong p-d type charge transfer character of the system, with band gap proportional to average charge transfer energy of Ni2+ and Mn4+ ions.
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We report the formation of a non-magnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator LaTiO3 and the antiferromagnetic charge transfer insulator LaFeO3. By density functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the t2g and eg bands. As a result of these two driving forces, the Fe 3d bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe 3d bands and reveals an unprecedented charge transfer up to 1.2+/-0.2 e-/interface unit cell in our LaTiO3/LaFeO3 heterostructures.
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We explore the electronic band structure of free standing monolayers of chromium trihalides, CrXtextsubscript{3}{, X= Cl, Br, I}, within an advanced emph{ab-initio} theoretical approach based in the use of Greens function functionals. We compare the local density approximation with the quasi-particle self-consistent emph{GW} approximation (QSemph{GW}) and its self-consistent extension (QS$Gwidehat{W}$) by solving the particle-hole ladder Bethe-Salpeter equations to improve the effective interaction emph{W}. We show that at all levels of theory, the valence band consistently changes shape in the sequence Cl{textrightarrow}Br{textrightarrow}I, and the valence band maximum shifts from the M point to the $Gamma$ point. However, the details of the transition, the one-particle bandgap, and the eigenfunctions change considerably going up the ladder to higher levels of theory. The eigenfunctions become more directional, and at the M point there is a strong anisotropy in the effective mass. Also the dynamic and momentum dependent self energy shows that QS$Gwidehat{W}$ adds to the localization of the systems in comparison to the QSemph{GW} thereby leading to a narrower band and reduced amount of halogens in the valence band manifold.
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