Effects of 5d electrons and spin-orbit interaction on the characteristics of bulk plasmons in lead

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).An ab initio study of the dynamical dielectric response of bulk lead is presented. The influence of the 5d semicore states on the characteristics of the bulk plasmon is analyzed by means of first-principles pseudopotential calculations. The effects of spin-orbit interactions and local-fields are also studied in detail. The inclusion of the 5d semicore states in the valence configuration completely changes the high-energy-transfer dielectric properties of bulk Pb. In particular, it lowers the computed bulk plasmon energy by about 3.5 eV, bringing its frequency to good agreement with experimental data. In general, the high-energy-transfer dielectric response of bulk Pb is found to be shaped mostly by the interplay between the interband transitions involving the semicore 5d states and the spin-orbit coupling interaction. Local-field effects are found to affect the relative spectral weight of the high-energy excitations, while leaving their dispersion mostly unaffected.We acknowledge financial support from the Spanish MINECO (Grant No. FIS2013-48286-C2-1-P), the Departamento de Educacion del Gobierno Vasco, and the University of the Basque Country (Grant No. GIC07-IT-366-07).Peer Reviewe

Ab initio study of low-energy collective electronic excitations in bulk Pb

A theoretical study of the dynamical dielectric response of bulk lead at low energies is presented. The calculations are performed with full inclusion of the electronic band structure calculated by means of a first-principles pseudopotential approach. The effect of inclusion of the spin-orbit interaction in the band structure on the excitation spectra in Pb is analyzed, together with dynamical exchange-correlation and local-field effects. In general, results show significant anisotropy effects on the dielectric response of bulk Pb. At small momentum transfers along three different high-symmetry directions, the calculated excitation spectra present several peaks with strong acousticlike dispersion in the energy range below 2 eV. The analysis shows that only one of such modes existing at momentum transfers along the Γ-K direction can be interpreted as a true acousticlike plasmon, whereas all other modes are originated from the enhanced number of intraband electron-hole excitations at corresponding energies. Comparison with available optical experimental data shows good agreement. © 2013 American Physical Society.We acknowledge financial support from the Spanish MICINN (Grant No. FIS2010-19609-C02-01), the Departamento de Educación del Gobierno Vasco, and the University of the Basque Country (Grant No. GIC07-IT-366-07).Peer Reviewe

First principles quasiparticle damping rates in bulk lead

First principles calculations of the damping rates (inverse inelastic lifetimes) of low energy quasiparticles in bulk Pb are presented. Damping rates are obtained both for excited electrons and holes with energies up to 8 eV on a set of k vectors throughout the Brillouin zone (BZ). Strong localization effects in the calculated lifetimes are found. Averaged over the BZ inelastic lifetimes versus quasiparticle energy are reported as well. In addition, the effect of the spin-orbit induced splitting in the band structure on the calculated lifetimes in Pb is investigated.Comment: 10 pages, 8 figures, 5 table

Exchange interaction and its tuning in magnetic binary chalcogenides

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.Using a first-principles Green's function approach we study magnetic properties of the magnetic binary tetradymite chalcogenides Bi2Se3, Bi2Te3, and Sb2Te3. The magnetic coupling between transition-metal impurities is long range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into exchange interactions in magnetic binary tetradymite chalcogenides and open a way to design new materials for promising applications.We acknowledge support by the Tomsk State University Competitiveness Improvement Program and the Deutsche Forschungsgemeinschaft (Priority Program SPP 1666 “Topological Insulators”).Peer Reviewe

Exchange interaction and its tuning in magnetic binary chalcogenides

Using a first-principles Green's function approach we study magnetic properties of the magnetic binary chalcogenides Bi2Te3, Bi2Se3, and Sb2Te3. The magnetic coupling between transition-metal impurities is long-range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into magnetic interactions in magnetic binary chalcogenides and open a way to design new materials for promising applications

Expansion of Human Limbal Epithelial Stem/Progenitor Cells Using Different Human Sera: A Multivariate Statistical Analysis

Transplantation of human cultured limbal epithelial stem/progenitor cells (LESCs) has demonstrated to restore the integrity and functionality of the corneal surface in about 76% of patients with limbal stem cell deficiency. However, there are different protocols for the expansion of LESCs, and many of them use xenogeneic products, being a risk for the patients’ health. We compared the culture of limbal explants on the denuded amniotic membrane in the culture medium—supplemental hormone epithelial medium (SHEM)—supplemented with FBS or two differently produced human sera. Cell morphology, cell size, cell growth rate, and the expression level of differentiation and putative stem cell markers were examined. Several bioactive molecules were quantified in the human sera. In a novel approach, we performed a multivariate statistical analysis of data to investigate the culture factors, such as differently expressed molecules of human sera that specifically influence the cell phenotype. Our results showed that limbal cells cultured with human sera grew faster and contained similar amounts of small-sized cells, higher expression of the protein p63α, and lower of cytokeratin K12 than FBS cultures, thus, maintaining the stem/progenitor phenotype of LESCs. Furthermore, the multivariate analysis provided much data to better understand the obtaining of different cell phenotypes as a consequence of the use of different culture methodologies or different culture components.Research study supported by grants from Mutua Madrileña Foundation (FMM11/02), Basque Foundation for Health Research and Innovation BIOEF (BIO14/TP/002), National Eye Institute (R01EY021797), California Institute for Regenerative Medicine (TR-TR2-01768 and CLIN1-08686) and an unrestricted grant from Research to Prevent Blindness to the Department of Ophthalmology, University of California, Los Angeles. R.H.-M. was supported by fellowships from the University of the Basque Country UPV/EHU and the Jesus de Gangoiti Barrera foundation

Surface alloying and iron selenide formation in Fe/Bi2Se3(0001) observed by x-ray absorption fine structure experiments

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.The atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator Bi2Se3 is analyzed by surface x-ray absorption spectroscopy. Iron atoms deposited on a Bi2Se3 (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer. Iron atoms are neighbored by six selenium atoms at a distance in the 2.4 Å range indicating substantial atomic relaxations. Mild annealing up to 520 K leads to the formation of α-FeSe, characterized by a local order extending up to the sixth shell (5.80 Å). Ab initio calculations predict a noncollinear magnetic ordering with a transition temperature of 3.5-10 K depending on the iron concentration and the number of the layers in which Fe is located.We acknowledge financial support from DFG through priority program SPP1666 (Topological Insulators). M.M.O. and E.V.C. thank the Tomsk State University Academic D. I. Mendeleev Fund Program (Research Grant No. 8.1.05.2015). Partial support by the Saint Petersburg State University Project No. 11.50.202.2015 is also acknowledged.Peer Reviewe