Search results for "angle-resolved photoemission spectroscopy"
showing 10 items of 51 documents
Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides
2016
Using a second-order perturbative Green's functions approach we determined the normal state single-particle spectral function $A(\vec{k},\omega)$ employing a minimal effective model for iron-based superconductors. The microscopic model, used before to study magnetic fluctuations and superconducting properties, includes the two effective tight-binding bands proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and inter-orbital local electronic correlations, related to the Fe-3d orbitals. Here, we focus on the study of normal state electronic properties, in particular the temperature and doping dependence of the total density of states, $A(\omega)$, and of $A(\vec{k},\o…
Electron-spectroscopic investigations on ternary HFS: CeT2X2
1997
Investigations of the electronic properties were carried out for ternary Ce-based heavy fermion systems. The well-ordered surfaces of HFS were prepared by MBE on W (110) with subsequent annealing. The layers are characterised by MEED, LEED, AES and XPS. For the electron-spectroscopic investigations, ARUPS and SPEELS were used. In the photoemission spectra, dispersion effects could be detected. By means of SPEELS, the dipole-forbidden Ce f-f transitions could be observed. The comparison of the energy loss spectra above and below the characteristic temperature T∗ reveals differences in the energy losses as well as in the asymmetries.
Phonon Driven Floquet Matter.
2018
The effect of electron–phonon coupling in materials can be interpreted as a dressing of the electronic structure by the lattice vibration, leading to vibrational replicas and hybridization of electronic states. In solids, a resonantly excited coherent phonon leads to a periodic oscillation of the atomic lattice in a crystal structure bringing the material into a nonequilibrium electronic configuration. Periodically oscillating quantum systems can be understood in terms of Floquet theory, which has a long tradition in the study of semiclassical light-matter interaction. Here, we show that the concepts of Floquet analysis can be applied to coherent lattice vibrations. This coupling leads to p…
Survival of Floquet–Bloch States in the Presence of Scattering
2021
Floquet theory has spawned many exciting possibilities for electronic structure control with light, with enormous potential for future applications. The experimental demonstration in solids, however, remains largely unrealized. In particular, the influence of scattering on the formation of Floquet-Bloch states remains poorly understood. Here we combine time- and angle-resolved photoemission spectroscopy with time-dependent density functional theory and a two-level model with relaxation to investigate the survival of Floquet-Bloch states in the presence of scattering. We find that Floquet-Bloch states will be destroyed if scattering-activated by electronic excitations-prevents the Bloch elec…
Optical magnetic circular dichroism in threshold photoemission from a magnetite thin film
2011
Threshold photoemission excited by polarization-modulated ultraviolet femtosecond laser light is exploited for phase-sensitive detection of magnetic circular dichroism (MCD) for a magnetite thin film. Magnetite (Fe(3)O(4)) shows a magnetic circular dichroism of ∼(4.5 ± 0.3) × 10(-3) for perpendicularly incident circularly polarized light and a magnetization vector switched parallel and antiparallel to the helicity vector by an external magnetic field. The asymmetry in threshold photoemission is discussed in comparison to the magneto-optical Kerr effect. The optical MCD contrast in threshold photoemission will provide a basis for future laboratory photoemission studies on magnetic surfaces.
Observation of quantized subband states and evidence for surface electron accumulation in CdO from angle-resolved photoemission spectroscopy
2008
The electronic structure of well-ordered single-crystal thin films of CdO100 has been studied using angleresolved photoemission spectroscopy. Quantized electron subbands are observed above the valence-band maximum. The existence of these states provides evidence of an intrinsic electron accumulation space-charge layer near the CdO surface, an interpretation supported by coupled Poisson-Schrodinger calculations. The origin of the accumulation layer result is discussed in terms of the bulk band structure of CdO calculated using quasiparticle-corrected density-functional theory, which reveals that the conduction-band minimum at the Brillouin-zone center lies below the charge neutrality level.
Magnetic dichroism in photoemission with unpolarized light.
1994
A magnetic dichroism in photoemission from ferromagnets induced by unpolarized light is observed for the first time in the valence band region as well as for surface states. The study was carried out with magnetized Fe(110), Co(0001), and Gd(0001) films grown epitaxially on W(110). This phenomenon leads to an intensity asymmetry for opposite directions of the sample magnetization. It can be easily used for a routine laboratory diagnostic of magnetic behavior. A simple theoretical interpretation of the phenomenon based on the atomic model is given.
X-ray photoemission studies of the electronic structure of single-crystalline CdO(100)
2007
The electronic structure of single-crystalline CdO is investigated using X-ray photoemission spectroscopy. The surface is prepared by in situ Ar+ ion bombardment and annealing (IBA). The core level spectra before and after the IBA are presented, and reveal a dramatic reduction in the surface contamination. The semi-core Cd 4d level and valence band region following the IBA are also shown. The surface Fermi level is pinned 1.3 +/- 0.10 eV above the valence band maximum. (c) 2007 Elsevier Ltd. All rights reserved.
Refractory metal reactivity towards oxide surface : W/TiO2(1 1 0) case.
2006
International audience; Reactivity of deposited tungsten towards TiO2(1 1 0) surface was studied using synchrotron radiation photoemission spectroscopy (both core levels, valence band and resonant photoemission) on Materials Science Beamline at ELETTRA. W depositions carried out at room temperature on TiO2(1 1 0) surface give rise to an interfacial reaction which leads to a metastable situation due to kinetic limitations. Annealing induces chemical changes which are function of the initial coverage; for fractional coverage, annealing induces completion of oxidation of deposit whereas reduction to metallic tungsten occurs for highest coverage. These results demonstrate that interaction of W …
Chemical stability of the magnetic oxide EuO directly on silicon observed by hard x-ray photoemission spectroscopy
2011
We present a detailed study of the electronic structure and chemical state of high-quality stoichiometric EuO and O-rich ${\mathrm{Eu}}_{1}{\mathrm{O}}_{1+x}$ thin films grown directly on silicon without any buffer layer using hard x-ray photoemission spectroscopy (HAXPES). We determine the EuO oxidation state from a consistent quantitative peak analysis of $4f$ valence band and $3d$ core-level spectra. The results prove that nearly ideal, stoichiometric, and homogeneous EuO thin films can be grown on silicon, with a uniform depth distribution of divalent Eu cations. Furthermore, we identify the chemical stability of the EuO/silicon interface from Si $2p$ core-level photoemission. This work…