Frederik Schiller

Bio: Frederik Schiller is an academic researcher from Spanish National Research Council. The author has contributed to research in topics: Vicinal & Surface states. The author has an hindex of 20, co-authored 68 publications receiving 971 citations. Previous affiliations of Frederik Schiller include University of the Basque Country & Dresden University of Technology.

Antiferromagnetism, valence fluctuation, and heavy-fermion behavior in EuCu2(Ge1-xSix)2

Abstract: We have investigated the magnetic, thermodynamic, transport, and electronic properties across the transition from the divalent antiferromagnetic state to the valence fluctuating state of Eu in the alloy ${\mathrm{EuCu}}_{2}({\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Si}}_{x}{)}_{2}.$ The antiferromagnetic state is very stable from $x=0$ up to $x=0.6$ and disappears rather abruptly at ${x}_{c}\ensuremath{\approx}0.65.$ Near the crossover, we confirmed a pronounced Kondo-like behavior in the resistivity and in the thermopower. Further on, for x slightly larger than ${x}_{c},$ we observe the formation of a heavy Fermi liquid at low temperatures, as evidenced by a large linear coefficient of the specific heat $(\ensuremath{\gamma}=191{\mathrm{m}\mathrm{J}/\mathrm{K}}^{2}\mathrm{mol}$ for $x=0.7),$ a large quadratic term in the resistivity and a strongly enhanced constant susceptibility ${\ensuremath{\chi}}_{0}.$ This is a unique observation of heavy fermion behavior in a Eu compound. The photoemission spectra of the Eu $4f$ and $3d$ core levels indicate significant valence fluctuation even for $xl{x}_{c}$ in the magnetically ordered regime. The decrease of ${T}_{N}$ before reaching the critical point as well as the Kondo and the heavy fermion behavior found near ${x}_{c}$ are in strong contrast to the observation in typical Eu systems, which usually show a first-order transition from a (almost) divalent state to a strongly valence fluctuating Eu state.

X-ray photoemission analysis of clean and carbon monoxide-chemisorbed platinum(111) stepped surfaces using a curved crystal

Abstract: Surface chemistry and catalysis studies could significantly gain from the systematic variation of surface active sites, tested under the very same conditions. Curved crystals are excellent platforms to perform such systematics, which may in turn allow to better resolve fundamental properties and reveal new phenomena. This is demonstrated here for the carbon monoxide/platinum system. We curve a platinum crystal around the high-symmetry (111) direction and carry out photoemission scans on top. This renders the spatial core-level imaging of carbon monoxide adsorbed on a 'tunable' vicinal surface, allowing a straightforward visualization of the rich chemisorption phenomenology at steps and terraces. Through such photoemission images we probe a characteristic elastic strain variation at stepped surfaces, and unveil subtle stress-release effects on clean and covered vicinal surfaces. These results offer the prospect of applying the curved surface approach to rationally investigate the chemical activity of surfaces under real pressure conditions.

Fermi gap stabilization of an incommensurate two-dimensional superstructure.

Abstract: The compressed, incommensurate approximately (9.5 x 9.5) moire superstructure of the Ag monolayer on Cu(111) displays a filled surface state band with a Fermi energy gap at the Brillouin zone boundary. By contrast, the surface band is gapless for the less compressed, commensurate (9 x 9) moire of two Ag layers. A simple estimate of the energy gain rendered by opening this gap gives a value similar to the elastic energy change required to modify the commensurate structure, thereby suggesting that the approximately (9.5 x 9.5) incommensurate phase is stabilized by such a gap opening. The possible presence of a charge density wave state is discussed.

Structure and electronic properties of dysprosium-silicide nanowires on vicinal Si"001…

Abstract: Dysprosium-silicide nanowires with widths of 15–100 A and lengths exceeding several 1000 A can be formed on Si(001) by self-assembly. Because of the anisotropy of the Si(001) surface, these nanowires grow in two orthogonal directions. In this study we demonstrate that growth on vicinal substrates results in a perfect unidirectional alignment of the wires. This allows an investigation by angle-resolved photoelectron spectroscopy showing anisotropic metallicity of the nanowires.

Model potential for the description of metal/organic interface states

Abstract: We present an analytical one-dimensional model potential for the description of electronic interface states that form at the interface between a metal surface and flat-lying adlayers of π-conjugated organic molecules The model utilizes graphene as a universal representation of these organic adlayers It predicts the energy position of the interface state as well as the overlap of its wave function with the bulk metal without free fitting parameters We show that the energy of the interface state depends systematically on the bond distance between the carbon backbone of the adayers and the metal The general applicability and robustness of the model is demonstrated by a comparison of the calculated energies with numerous experimental results for a number of flat-lying organic molecules on different closed-packed metal surfaces that cover a large range of bond distances

Optical nano-imaging of gate-tunable graphene plasmons

Abstract: The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes However, because photons do not possess charge, a way of controlling them efficiently by electrical means has so far proved elusive A promising way to achieve electric control of light could be through plasmon polaritons—coupled excitations of photons and charge carriers—in graphene In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can readily be tuned electrically by varying the graphene carrier density Although evidence of optical graphene plasmon resonances has recently been obtained spectroscopically, no experiments so far have directly resolved propagating plasmons in real space Here we launch and detect propagating optical plasmons in tapered graphene nanostructures using near-field scattering microscopy with infrared excitation light We provide real-space images of plasmon fields, and find that the extracted plasmon wavelength is very short—more than 40 times smaller than the wavelength of illumination We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume The cavity resonance is controlled in situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors This successful alliance between nanoelectronics and nano-optics enables the development of active subwavelength-scale optics and a plethora of nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing, and strongly enhanced light–matter interactions for quantum devices and biosensing applications

All-Si valley-hall photonic topological insulator

Abstract: We propose an all-Si photonic topological insulator (PTI) that emulates the quantum-valley-Hall (QVH) effect with backscattering-free edge states. Such QVH-PTI has exotic external coupling property to vacuum and can be utilized for designing random resonant time-delay cavities immune to reflections.

Controlling a chemical coupling reaction on a surface: tools and strategies for on-surface synthesis

Abstract: On-surface synthesis is appearing as an extremely promising research field aimed at creating new organic materials. A large number of chemical reactions have been successfully demonstrated to take place directly on surfaces through unusual reaction mechanisms. In some cases the reaction conditions can be properly tuned to steer the formation of the reaction products. It is thus possible to control the initiation step of the reaction and its degree of advancement (the kinetics, the reaction yield); the nature of the reaction products (selectivity control, particularly in the case of competing processes); as well as the structure, position, and orientation of the covalent compounds, or the quality of the as-formed networks in terms of order and extension. The aim of our review is thus to provide an extensive description of all tools and strategies reported to date and to put them into perspective. We specifically define the different approaches available and group them into a few general categories. In the last part, we demonstrate the effective maturation of the on-surface synthesis field by reporting systems that are getting closer to application-relevant levels thanks to the use of advanced control strategies.

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.