Cantor Spectra for Double Exchange Model

We numerically study energy spectra and localization properties of the double exchange model at irrational filling factor. To obtain variational ground state, we use a mumerical technique in momentum space by ``embedded'' boundary condition which has no finite size effect a priori. Although the Hamiltonian has translation invariance, the ground state spontaneously exhibits a self-similarity. Scaling and multi-fractal analysis for the wave functions are performed and the scaling indices $\alpha$'s are obtained. The energy spectrum is found to be a singular continuous, so-called the Cantor set with zero Lebesque measure.Comment: 4 pages, 4 figures, revtex, corrected some typos, accepted for publication in PR

Bulk Electronic structure of Na0.35_{0.35}CoO2_{2}.1.3H2_{2}O

High-energy (h$\nu$ = 5.95 keV) synchrotron Photoemission spectroscopy (PES) is used to study bulk electronic structure of Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O, the layered superconductor. In contrast to 3-dimensional doped Co oxides, Co $\it{2p}$ core level spectra show well-separated Co$^{3+}$ and Co$^{4+}$ ions. Cluster calculations suggest low spin Co$^{3+}$ and Co$^{4+}$ character, and a moderate on-site Coulomb correlation energy U$_{dd}\sim$3-5.5 eV. Photon dependent valence band PES identifies Co $\it{3d}$ and O $\it{2p}$ derived states, in near agreement with band structure calculations.Comment: 4 pages 4 figures Revised text added referenc

Dynamical mean-field approach to materials with strong electronic correlations

We review recent results on the properties of materials with correlated electrons obtained within the LDA+DMFT approach, a combination of a conventional band structure approach based on the local density approximation (LDA) and the dynamical mean-field theory (DMFT). The application to four outstanding problems in this field is discussed: (i) we compute the full valence band structure of the charge-transfer insulator NiO by explicitly including the p-d hybridization, (ii) we explain the origin for the simultaneously occuring metal-insulator transition and collapse of the magnetic moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of plane-wave pseudopotentials which allows us to compute the orbital order and cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a general explanation for the appearance of kinks in the effective dispersion of correlated electrons in systems with a pronounced three-peak spectral function without having to resort to the coupling of electrons to bosonic excitations. These results provide a considerable progress in the fully microscopic investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

Degradation of emerging contaminants: effect of thermal treatment on nb2o5 as photocatalyst

This study describes the use Nb2O5 catalysts – calcined at different temperatures (373–873 K) – in the photo-catalytic degradation reaction of four contaminants of emerging concern: acetylsalicylic acid (ASA), 17α-ethi-nylestradiol (EE2), ibuprofen (IBP) and paracetamol (PAR). The photocatalysts were characterized by different techniques – N2 adsorption/desorption, photoacoustic spectroscopy (PAS), Fourier Transform Infrared (FT-IR) and X-ray diffraction (XRD) – and applied in the photocatalytic degradation tests. Among the tested catalysts, non-calcined Nb2O5 showed the highest photocatalytic activity. The characterization results indicated that this catalyst presented an amorphous (non-crystalline) structure, low band gap and the highest surface area (SBET =182 m2 g-1). A design of experiments (DoE) methodology was applied in order to verify the effects of pH (4–10) and catalyst concentration (0.5–1.5 g L-1) in the four pollutants removal using the non-calcined Nb2O5. Ac-cording to the Experimental Design Analysis, a statistically significant linear effect with a negative coefficient was observed for pH in EE2, IBP and PAR photocatalytic degradation. Tests to verify the influence of the presence compounds together in the degradation reaction of each contaminant, suggested that the photocatalytic degradation of IBP occurs predominantly through the action of radicals O2•-, , with minor contribution from HO•.The authors are thankful to the Brazilian agencies CNPq, CAPES and Fundação Araucária for financial support of this work, C2MMa and Brazilian Mining and Metallurgy Company – CBMM. This work was financially supported by project CIMO (UIDB/00690/2020) through FEDER under Program PT2020.info:eu-repo/semantics/publishedVersio