A5026156471- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Advanced Chemical Physics Studies
- Advanced Condensed Matter Physics
- Quantum and electron transport phenomena
- Electron and X-Ray Spectroscopy Techniques
- Organic and Molecular Conductors Research
- Electronic and Structural Properties of Oxides
- Surface and Thin Film Phenomena
- Iron-based superconductors research
- X-ray Spectroscopy and Fluorescence Analysis
- Topological Materials and Phenomena
- 2D Materials and Applications
- Magnetic and transport properties of perovskites and related materials
- Magnetic properties of thin films
- Molecular Junctions and Nanostructures
- Graphene research and applications
- High-pressure geophysics and materials
- Copper-based nanomaterials and applications
- Inorganic Chemistry and Materials
- Advanced Materials Characterization Techniques
- ZnO doping and properties
- Nuclear Materials and Properties
- Semiconductor materials and interfaces
- Machine Learning in Materials Science
École Polytechnique Fédérale de Lausanne
2015-2024
École Polytechnique
1999-2010
Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine
2003-2006
University of Neuchâtel
1991-1997
Institut de Physique
1996
University of Lausanne
1993
Radboud University Nijmegen
1987-1992
Université Paris-Sud
1987-1991
University of Groningen
1988-1989
Université Paris Cité
1987-1989
The oxygen 1s x-ray-absorption edges of a series 3d-transition-metal oxides have been measured. structures at the edge arise from covalent mixing metal and states, which introduces p character in unoccupied states mainly character. spectra can be divided into two regions: first is double-peaked sharp structure near threshold, related to 3d states; second broader 5--10 eV above 4s 4p bands. We attribute up 15 threshold 2p data are analyzed terms ligand-field exchange splittings. It shown that...
Surface alloying is shown to produce electronic states with a very large spin-splitting. We discuss the long range ordered bismuth/silver(111) surface alloy where an energy bands separation of up one eV achieved. Such strong spin-splitting enables angular resolved photoemission spectroscopy directly observe region close band edge, density shows quasi-one dimensional behavior. The associated singularity in local has been measured by low temperature scanning tunneling spectroscopy....
The ultrafast dynamics of excited carriers in graphene is closely linked to the Dirac spectrum and plays a central role for many electronic optoelectronic applications. Harvesting energy from electron-hole pairs, instance, only possible if these pairs can be separated before they lose vibrations, merely heating lattice. While hot carrier could so far accessed indirectly, we here present direct time-resolved view on cone by angle-resolved photoemission (ARPES). This allows us show...
The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in energy range from 300 to 1600 eV intended for resonant inelastic scattering (RIXS) angle-resolved photoelectron spectroscopy (ARPES) are described. photon source is an undulator novel fixed-gap design where longitudinal movement permanent magnetic arrays controls not only light polarization (including circular 0-180 degrees rotatable linear polarizations) but also without changing gap....
Oxygen vacancies created in anatase TiO(2) by UV photons (80-130 eV) provide an effective electron-doping mechanism and induce a hitherto unobserved dispersive metallic state. Angle resolved photoemission reveals that the quasiparticles are large polarons. These results indicate can be tuned from insulator to polaron gas weakly correlated metal as function of doping clarify nature conductivity this material.
Anatase TiO2 is among the most studied materials for light-energy conversion applications, but nature of its fundamental charge excitations still unknown. Yet it crucial to establish whether light absorption creates uncorrelated electron-hole pairs or bound excitons and, in latter case, determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that direct...
We have used x-ray-absorption spectroscopy to study a series of compounds in which Cu assumes formal valence between 0 and 3. find that the shape, threshold energy, intensity ${L}_{3}$ absorption edge is strongly influenced by chemical state atoms. use 2p spectra large number compounds, including sulfides, oxides, La-Sr-Cu-O phthalocyanine complex, various minerals show presence strong 2p-3d excitonic transition fingerprint Cu(${d}^{9}$) contribution ground state. A simple ionic picture...
We present a 5m long spectrometer for soft x rays to be used at synchrotron radiation beamline resonant x-ray emission spectroscopy and inelastic scattering in the 400–1600eV energy range. It is based on variable line spacing spherical grating (average groove density of 3200mm−1, R=58.55m) charge coupled device two dimensional detector. With an spot sample 10μm, targeted resolving power higher than 10 000 all energies below 1100eV better 7000 1500eV. The off-line tests made with Al MgKα1,2...
We have carried out high-resolution photoemission experiments on two quasi-one-dimensional compounds: ${\mathrm{K}}_{0.3}$${\mathrm{MoO}}_{3}$ and (${\mathrm{TaSe}}_{4}$${)}_{2}$I. In both systems, a metal-insulator transition associated with lattice distortion is reported. show that the Fermi-step characteristic of metallic phase not observed above Peierls temperature. As this Fermi step always in higher-dimensional metals, we propose behavior results from singular properties...
We report the near-edge x-ray absorption fine-structure (NEXAFS) spectrum of a single layer graphite (graphene) obtained by micromechanical cleavage highly ordered pyrolytic on SiO2 substrate. utilized photoemission electron microscope to separately study single-, double-, and few-layers graphene samples. In single-layer we observe splitting pi resonance clear signature predicted interlayer state. The NEXAFS data illustrate rapid evolution electronic structure with increased number layers.
We demonstrate a giant Rashba-type spin splitting on semiconducting substrate by means of Bi-trimer adlayer Si(111) wafer. The in-plane inversion symmetry is broken inducing with Rashba energy about 140 meV, much larger than what has previously been reported for any semiconductor heterostructure. separation the electronic states their lifetime broadening, which directly observed angular resolved photoemission spectroscopy. experimental results are confirmed relativistic first-principles calculations.
Abstract Two series of experiments on well‐characterized systems were performed to examine the probing depth soft x‐ray absorption spectroscopy (XAS) measured in total‐electron‐yield (TEY) mode. First we Ni 2 p 3/2 spectra Ni(100) covered with Tb as a function overlayer thickness. Secondly recorded O 1s Ta 5 films produced by controlled anodic oxidatio foils oxide The mean (MPD) was found be much shorter than previously assumed (for 1s, only 1.9 nm). relative importance those cascade...
A detailed x-ray absorption study of the oxygen $K$ edge $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ is presented. preedge peak observed for all samples with $x\ensuremath{\ge}6.4$ which we argue to be due holes in $\mathrm{O} 2p$ band. By comparison ${\mathrm{Li}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}\mathrm{O}$ $x$ dependence number determined.
We observe a giant spin-orbit splitting in bulk and surface states of the non-centrosymmetric semiconductor BiTeI. show that Fermi level can be placed valence or conduction band by controlling termination. In both cases it intersects spin-polarized bands, corresponding depletion accumulation layers. The momentum these bands is not affected adsorbate-induced changes potential. These findings demonstrate two properties crucial for enabling semiconductor-based spin electronics -- large, robust...
We measured high resolution Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS) of the undoped cuprates La$_2$CuO$_4$, Sr$_2$CuO$_2$Cl$_2$, CaCuO$_2$ and NdBa$_2$Cu$_3$O$_6$. The dominant spectral features were assigned to $dd$ excitations we extensively studied their polarization geometry dependence. In a pure ionic picture, calculated theoretical cross sections for those used them fit experimental data with excellent agreement. By doing so, able determine energy symmetry Cu-3$d$...
The dynamics of excited electrons and holes in single layer (SL) MoS$_2$ have so far been difficult to disentangle from the excitons that dominate optical response this material. Here, we use time- angle-resolved photoemission spectroscopy for a SL on metallic substrate directly measure free carriers. This allows us ascertain direct quasiparticle band gap 1.95 eV determine an ultrafast (50 fs) extraction carriers via metal contact with MoS$_2$. process is key importance optoelectronic...
High-resolution x-ray absorption measurements reveal a rare-earth-dependent splitting of the $\text{Ni}\text{ }K$ edge in insulating, charge-disproportionated state whole $R{\text{NiO}}_{3}$ perovskite family. The is five times larger for ${\text{LuNiO}}_{3}$ [2.5(1) eV] than ${\text{PrNiO}}_{3}$ [0.5(3) eV], suggesting that charge transfer between ${\text{Ni}}^{3+\ensuremath{\delta}}$ and ${\text{Ni}}^{3\ensuremath{-}\ensuremath{\delta}}$ decreases by approaching itinerant limit heavier...
Bilayer graphene is a highly promising material for electronic and optoelectronic applications since it supporting massive Dirac fermions with tunable band gap. However, no consistent picture of the gap's effect on optical transport behavior has emerged so far, been proposed that insulating nature gap could be compromised by unavoidable structural defects, topological in-gap states, or structure altogether changed many-body effects. Here, we directly follow excited carriers in bilayer...
Time- and angle-resolved photoemission measurements on two doped graphene samples displaying different doping levels reveal remarkable differences in the ultrafast dynamics of hot carriers Dirac cone. In more strongly ($n$-)doped graphene, we observe larger carrier multiplication factors ($>$ 3) a significantly faster phonon-mediated cooling back to equilibrium compared less ($p$-)doped graphene. These results suggest that careful tuning level allows for an effective manipulation graphene's...
Lead-halide perovskite (LHP) semiconductors are emergent optoelectronic materials with outstanding transport properties which not yet fully understood. We find signatures of large polaron formation in the electronic structure inorganic LHP CsPbBr$_3$ by means angle-resolved photoelectron spectroscopy. The experimental valence band dispersion shows a hole effective mass $0.26\pm0.02\,\,m_e$, 50% heavier than bare $m_0 =0.17 m_e$ predicted density functional theory. Calculations...
Trigonal tellurium, a small-gap semiconductor with pronounced magneto-electric and magneto-optical responses, is among the simplest realizations of chiral crystal. We have studied by spin- angle-resolved photoelectron spectroscopy its unconventional electronic structure unique spin texture. identify Kramers-Weyl, composite, accordionlike Weyl fermions, so far only predicted theory, show that polarization parallel to wave vector along lines in k space connecting high-symmetry points. Our...
When electrons are subject to a potential with two incommensurate periods, translational invariance is lost, and no periodic band structure expected. However, model calculations based on nearly free one-dimensional experimental results from high-resolution photoemission spectroscopy quasi–one-dimensional material do show dispersing states signatures of both periodicities. Apparent structures generated by the nonuniform distribution electronic spectral weight over complex eigenvalue spectrum.
X-ray-absorption measurements at the Cu ${\mathit{L}}_{2,3}$ and O K edges of ${\mathrm{Cu}}_{2}$O reveal presence unoccupied states predominantly d p character bottom conduction band. We find that spectral features up to 25 eV from threshold can be assigned structures in calculated density states, projected on sites. However, for a satisfactory description anomalous line shape intensity edges, core hole created absorption process must included calculation. have investigated this effect by...
Abstract In this paper we review the present status of electron spectroscopy Ce and Yb Kondo systems, with particular emphasis on photoemission inverse photoemission. Our starting point is situation in mid-1980s, characterized by development a ‘Kondo scenario’ for thermodynamic spectral properties, as described Allen et al. (1986, Adv. Phys., 35, 275). That picture, based room-temperature results T = 0 approach to impurity Anderson Hamiltonian, has been generally confirmed better defined...