A5062407060- Topological Materials and Phenomena
- Graphene research and applications
- Quantum and electron transport phenomena
- Magnetic properties of thin films
- 2D Materials and Applications
- Advanced Condensed Matter Physics
- Molecular Junctions and Nanostructures
- Physics of Superconductivity and Magnetism
- Electronic and Structural Properties of Oxides
- Surface and Thin Film Phenomena
- ZnO doping and properties
- Force Microscopy Techniques and Applications
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Iron-based superconductors research
- Advanced Chemical Physics Studies
- High-pressure geophysics and materials
- Zeolite Catalysis and Synthesis
- Inorganic Chemistry and Materials
- Rare-earth and actinide compounds
- Advancements in Battery Materials
- Organic and Molecular Conductors Research
- Theoretical and Computational Physics
- Material Properties and Failure Mechanisms
- Stochastic Gradient Optimization Techniques
École Polytechnique Fédérale de Lausanne
2012-2021
The Open University
2009-2012
City, University of London
2009-2012
CEA Paris-Saclay
2006-2008
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2006-2008
Direction des énergies
2008
Laboratoire de Physique des Interfaces et des Couches Minces
2008
Institut Rayonnement-Matière de Saclay
2008
Service de Physique de l'État Condensé
2007
CEA Paris-Saclay - Etablissement de Saclay
2006-2007
The intense theoretical and experimental interest in topological insulators semimetals has established band structure topology as a fundamental material property. Consequently, identifying topologies become an important, but often challenging problem, with no exhaustive solution at the present time. In this work we compile series of techniques, some previously known, that allow for to problem large set possible topologies. method is based on tracking hybrid Wannier charge centers computed...
Abstract A Weyl semimetal possesses spin-polarized band-crossings, called nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave same as massless fermions, leading to exotic properties like chiral anomaly. To have transport dominated nodes need locate nearly at chemical potential and enclosed pairs of individual Fermi surfaces with non-zero Chern numbers. Combining angle-resolved photoemission spectroscopy first-principles calculation, here...
The recently discovered type-II Weyl points appear at the boundary between electron and hole pockets. Type-II semimetals that host such are predicted to exhibit a new type of chiral anomaly possess thermodynamic properties very different from their type-I counterparts. In this Letter, we describe prediction semimetal phase in transition metal diphosphides MoP2 WP2. These materials characterized by relatively simple band structures with four pairs points. Neighboring have same chirality,...
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...
The complex electronic properties of ${\mathrm{ZrTe}}_{5}$ have recently stimulated in-depth investigations that assigned this material to either a topological insulator or 3D Dirac semimetal phase. Here we report comprehensive experimental and theoretical study both structural ${\mathrm{ZrTe}}_{5}$, revealing the bulk is strong (STI). By means angle-resolved photoelectron spectroscopy, identify at top valence band surface state. dispersion these bands well captured by ab initio calculations...
We report on the magnetic properties of single Co atoms graphene Pt(111). By means scanning tunneling microscopy spin-excitation spectroscopy, we infer a anisotropy K=-8.1 meV with out-of-plane hard axis and moment 2.2μ(B). adsorbs sixfold hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their very different from those clean Co. Ab initio calculations support our results reveal that large stems strong ligand field effects due to interaction...
Atomically precise tailoring of graphene can enable unusual transport pathways and new nanometer-scale functional devices. Here we describe a recipe for the controlled production highly regular "5-5-8" line defects in by means simultaneous electron irradiation Joule heating applied electric current. High-resolution transmission microscopy reveals individual steps growth process. Extending earlier theoretical work suggesting valley-discriminating capabilities 5-5-8 defect, perform...
BiTeI is a giant Rashba spin splitting system, in which non-centro symmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, pressures up $15$ GPa. The gap feature conductivity vanishes above $p \sim 9$ GPa does not reappear at least plasma edge, associated with intrinsically doped charge carriers, smeared out through transition $9$ Using pressure Raman spectroscopy, we follow...
The magnetic properties of iron (spin and orbital moments, magnetocrystalline anisotropy energy) in various geometries dimensionalities are investigated by using a parametrized tight-binding model an s, p d atomic basis set including spin polarization the effect spin–orbit coupling. validity this is well established comparing results with those obtained ab initio code. This applied to study bulk bcc fcc phases, (110) (001) surfaces monatomic wire, at several interatomic distances. New...
Distinct to type-I Weyl semimetals (WSMs) that host quasiparticles described by the equation, energy dispersion of in type-II WSMs violates Lorentz invariance and cones momentum space are tilted. Since it was proposed fermions could emerge from (W,Mo)Te2 (W,Mo)P2 families materials, a large numbers experiments have been dedicated unveil possible manifestation WSM, e.g. surface-state Fermi arcs. However, interpretations experimental results very controversial. Here, using angle-resolved...
Nanoelectromechanical systems constitute a class of devices lying at the interface between fundamental research and technological applications. Realizing nanoelectromechanical based on novel materials such as graphene allows studying their mechanical electromechanical characteristics nanoscale addressing questions electron-phonon interaction bandgap engineering. In this work, we realize using single bilayer probe interplay electrical properties. We show that deflection monolayer nanoribbons...
We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)2I performed by means angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. find it to be zero-gap semiconductor in non-distorted structure, with non-negligible interchain coupling. Theory experiment support Peierls-like scenario for CDW formation below T_CDW = 263 K, where incommensurability is direct consequence finite The small polarons, strongly suggested ARPES...
The electronic and magnetic properties of individual Fe atoms adsorbed on the surface topological insulator Bi$_2$Te$_3$(111) are investigated. Scanning tunneling microscopy spectroscopy prove existence two distinct types species, while our first-principles calculations assign them to adatoms in hcp fcc hollow sites. combination x-ray circular dichroism measurements angular dependent magnetization curves reveals out-of-plane anisotropies for both species with anisotropy constants...
Recent advances in large-scale synthesis of graphene and other 2D materials have underscored the importance local defects such as dislocations grain boundaries (GBs), especially their tendency to alter electronic properties material.Understanding how polycrystalline morphology affects is crucial for development applications flexible electronics, energy harvesting devices or sensors.We here report on atomic scale characterization several GBs structural-dependence localized states...
The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence topologically protected degeneracies near Fermi level. These are source exotic phenomena, including realization chiral fermions as quasiparticles in bulk and formation arc states on surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with band topology performing angle-resolved photoemission spectroscopy, supported first-principles...
Hydrogen adatoms and other species covalently bound to graphene act as resonant scattering centers affecting the electronic transport properties inducing Anderson localization. We show that attractive interactions between on their diffusion mobility strongly modify spatial distribution, thus fully eliminating isolated increasing population of larger size adatom aggregates. Such correlation is found influence disordered graphene. Our scaling analysis shows such aggregation increases...
Type-II Weyl semimetals (WSM) are topological materials characterized by special points (WP) in momentum space where the valence and conduction band touch. A WSM phase is predicted MoTe${}_{2}$ below 250 K, but WP located unoccupied part of electronic structure has eluded direct observation. By means time- angle-resolved photoemission, authors reveal fingerprint ultrafast electron dynamics. Electrons that optically excited into relax faster than high-temperature or topologically trivial...
We report a detailed study of the transport properties $\ensuremath{\beta}\ensuremath{-}\mathrm{B}{\mathrm{i}}_{4}{\mathrm{I}}_{4}$ quasi-one-dimensional topological insulator. Electrical resistivity, thermoelectric power, thermal conductivity, and Hall coefficient measurements are consistent with possible appearance charge-density-wave order at low temperatures. Both electrons holes contribute to conduction in dominant type charge carrier changes temperature as consequence...
Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices, because of the coexistence spin-split bulk and surface states, along with ambipolar character charge carriers. The need studying spin texture strongly spin-orbit coupled materials has recently promoted circular dichroic Angular Resolved Photoelectron Spectroscopy (cd-ARPES) an indirect tool to measure angular degrees freedom. Here we report a detailed photon energy dependent...
By performing angle-resolved photoemission spectroscopy and first-principles calculations, we address the topological phase of CaAgP investigate transition in $\mathrm{CaAg}({\mathrm{P}}_{1\text{\ensuremath{-}}x}\mathrm{A}{\mathrm{s}}_{x})$. We reveal that CaAgP, bulk band gap surface states with a large bandwidth are topologically trivial, agreement hybrid density functional theory calculations. The calculations also indicate application ``negative'' hydrostatic pressure can transform...
Fe atoms adsorbed on Cu(111) have been used as an atomic-scale model system for performing spin-based logic operations and to build the smallest stable magnet. In pursuit of understanding strength adatom/substrate hybridization in this system, small clusters down single a surface were studied using X-ray Absorption Spectroscopy Magnetic Circular Dichroism experiments. The spin orbital moments well magnetic anisotropy energies extracted experimentally compared with density functional theory...
We present a theoretical study of spin polarized transport in Fe atomic contacts by using self-consistent tight-binding Hamiltonian nonorthogonal $s$, $p$, and $d$ basis set, the polarization being obtained from noncollinear Stoner-like model transmission probability Fisher--Lee formula. The behavior an infinite perfect wire is compared to that chain presenting geometric defects or magnetic walls finite connected one-dimensional three-dimensional leads. In presence contacts, electrons much...