Periodically rippled graphene: growth and spatially resolved electronic structure

We studied the growth of an epitaxial graphene monolayer on Ru(0001). The graphene monolayer covers uniformly the Ru substrate over lateral distances larger than several microns reproducing the structural defects of the Ru substrate. The graphene is rippled with a periodicity dictated by the difference in lattice parameter between C and Ru. The theoretical model predict inhomogeneities in the electronic structure. This is confirmed by measurements in real space by means of scanning tunnelling spectroscopy. We observe electron pockets at the higher parts of the ripples.Comment: 5 page

Estructura electrónica del Cd como impureza en Si

Se analiza la estructura electrónica del Cd como impureza en Si. Utilizando el método de Huckel extendido, se presentan resultados de clusters para impurezas de Cd en sitios sustitucionales e intersticiales de simetría tetrahédrica. Los niveles profundos obtenidos experimentalmente en el gap del Si pueden explicarse a partir de la geometría sustitucional, siempre que se distorsionen los primeros vecinos del Cd según una relajación que conserve la simetría Td, junto con pequeñas distorsiones trigonales del Cd. Estos resultados son consistentes con la información experimental dada por experiencias de correlaciones angulares perturbadas y mediciones de efecto Hall.Facultad de Ciencias Exacta

Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6

Magnetic dc susceptibility ($\chi$) and electron spin resonance (ESR) measurements in the paramagnetic regime, are presented. We found a Curie-Weiss (CW) behavior for $\chi$(T) with a ferromagnetic $\Theta = 446(5)$ K and $\mu_{eff} = 4.72(9) \mu_{B}/f.u.$, this being lower than that expected for either $Fe^{3+}(5.9\mu_{B})$ or $Fe^{2+}(4.9\mu_{B})$ ions. The ESR g-factor $g = 2.01(2)$, is associated with $Fe^{3+}$. We obtained an excellent description of the experiments in terms of two interacting sublattices: the localized $Fe^{3+}$ ($3d^{5}$) cores and the delocalized electrons. The coupled equations were solved in a mean-field approximation, assuming for the itinerant electrons a bare susceptibility independent on $T$. We obtained $\chi_{e}^{0} = 3.7$ $10^{-4}$ emu/mol. We show that the reduction of $\mu_{eff}$ for $Fe^{3+}$ arises from the strong antiferromagnetic (AFM) interaction between the two sublattices. At variance with classical ferrimagnets, we found that $\Theta$ is ferromagnetic. Within the same model, we show that the ESR spectrum can be described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the absence of a $g$-shift. Surprisingly, as observed in CMR manganites, no narrowing effects of the ESR linewidth is detected in spite of the presence of the strong magnetic coupling. These results provide evidence that the magnetic order in $Sr_{2}FeMoO_{6}$ does not originates in superexchange interactions, but from a novel mechanism recently proposed for double perovskites

Avances en los estudios arqueológicos, geoarqueológicos y paleoambientales en las Sierras Orientales de Tandilia. Resultados preliminares de los sitios Alero El Mirador y Abrigo La Grieta

This paper presents the characteristics of the archaeological record of two sites recently taken up, called Alero El Mirador and Abrigo La Grieta. The study of different proxy data like lithic assemblages, zooarchaeological and paleoenvironmental record (obtained by diatoms, phytoliths and anthracology inferences) and their relationship to stratigraphic units, allows us to hypothesize anthropic management aspects of local natural resources and paleoclimatic events occurred in the eastern of Tandilia hill during different moments of the Pleistocene-Holocene archaeological sequence.Este trabajo presenta las características de los registros arqueológicos de dos sitios recientemente retomados, denominados Alero El Mirador y Abrigo La Grieta. Se dan a conocer los resultados del análisis de los conjuntos líticos, del registro zooarqueológico y paleoambiental (obtenidos a partir de la evidencias de diatomeas, antracología y fitolitos), y su relación con las unidades estratigráficas. Esta información proxy permite hipotetizar aspectos del manejo antrópico de recursos naturales locales y de eventos paleoclimáticos ocurridos en el sector serrano de Tandilia oriental durante distintos tramos de la secuencia Pleistoceno-Holoceno

Single Crystal EPR of the Mixed-Ligand Complex of Copper(II) with l‑Glutamic Acid and 1,10-Phenanthroline: A Study on the Narrowing of the Hyperfine Structure by Exchange

We report an EPR study at X- and Q-bands of polycrystalline and single crystal samples of the mixed copper­(II) complex with l-glutamic acid (glu) and 1,10-phenantroline (phen), [Cu­(glu)­(phen)­(H₂O)]⁺ NO₃^–·2­(H₂O). The polycrystalline sample spectrum at Q-band showed well resolved <i>g</i>_∥and <i>g</i>_⊥ features and partially solved hyperfine structure at <i>g</i>_∥, typical for weakly exchange coupled systems. This is confirmed from the angular variation of the EPR spectra which shows for certain magnetic field orientations a partially solved hyperfine structure characteristic of weak exchange, whereas a single Lorentzian line corresponding to strong exchange is observed for others. Analysis and simulation of the single crystal EPR spectra were performed using the random frequency modulation model of Anderson. Numerical simulations of the angular variation of the EPR spectra showed that the narrowing of the hyperfine structure is due to an exchange-mediated mechanism in which transitions between any pair of lines are equally likely. The exchange interaction responsible for this process is mediated by hydrophobic interactions between two phen molecules and a mixed chemical path of the type CuA–O_apH···O–C–O_eq–CuB, for which we evaluated an average isotropic exchange parameter |<i>J</i>| ≈ 25 × 10^–4 cm^–1