A5080080501- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic properties of thin films
- Characterization and Applications of Magnetic Nanoparticles
- Theoretical and Computational Physics
- Quantum and electron transport phenomena
- X-ray Diffraction in Crystallography
- Magnetic and transport properties of perovskites and related materials
- X-ray Spectroscopy and Fluorescence Analysis
- Nanoparticle-Based Drug Delivery
- Magnetism in coordination complexes
- High-pressure geophysics and materials
- Iron-based superconductors research
- Laser-Matter Interactions and Applications
- Advanced Thermodynamics and Statistical Mechanics
- Acoustic Wave Resonator Technologies
- Crystallography and Radiation Phenomena
- Advanced Fiber Laser Technologies
- Cold Atom Physics and Bose-Einstein Condensates
- Laser-Plasma Interactions and Diagnostics
- Ultrasound and Hyperthermia Applications
- Magnetic Properties and Applications
- Rare-earth and actinide compounds
- Organic and Molecular Conductors Research
- Electrostatics and Colloid Interactions
Laboratoire Procédés, Matériaux et Energie Solaire
2014-2024
Université de Perpignan
2010-2021
Centre National de la Recherche Scientifique
2013-2021
Paul Scherrer Institute
2009-2012
University of British Columbia
2007-2008
University of Waterloo
2007-2008
Pacific Institute for the Mathematical Sciences
2007
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2001-2006
CEA Paris-Saclay
2001-2006
École Polytechnique Fédérale de Lausanne
2004-2006
Using x-ray absorption (XAS) and resonant inelastic scattering (RIXS), charge dynamics at near the $\text{Fe}\text{ }L$ edges is investigated in Fe-pnictide materials contrasted to that measured other Fe compounds. It shown XAS RIXS spectra for 122 1111 pnictides are each qualitatively similar metal. Cluster diagonalization, multiplet, density-functional calculations show Coulomb correlations much smaller than cuprates, highlighting role of metallicity strong covalency these materials. The...
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...
The large variations of T$_c$ across the cuprate families is one major unsolved puzzles in condensed matter physics, and poorly understood. Although there appears to be a great deal universality cuprates, several orders magnitude changes can achieved through chemical composition structure unit cell. In this paper we formulate systematic examination electron-phonon coupling oxygen phonons incorporating number effects arising from aspects doping families. It argued that very sensitive probe...
We investigate magnetic excitations in the spin-ladder compound Sr_{14}Cu_{24}O_{41} using high-resolution Cu L_{3} edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast neutron scattering, cross section changes only moderately over entire Brillouin zone, revealing high sensitivity also at small momentum transfers, allowing determination of energy gap as 100 +/- 30 meV. results are backed by calculations...
We present an approach to computing multiplets for core spectroscopies, whereby the crystal field is constructed explicitly from positions and charges of surrounding atoms. The simplicity input allows consideration fields any symmetry in particular facilitates study spectroscopic effects arising low-symmetry environments. interplay between polarization directions can also be conveniently investigated. determination proceeds a Dirac density functional atomic calculation, followed by exact...
Motivated by the absence of cooperative Jahn-Teller effect and magnetic ordering in LiNiO$_2$, a layered oxide with triangular planes, we study general spin-orbital model on lattice. A mean-field approach reveals presence several singlet phases between SU(4) symmetric point ferromagnetic phase, conclusion supported exact diagonalizations finite clusters. We argue that one phases, characterized large number low-lying singlets associated to dimer coverings lattice, could explain properties...
The results of model calculations using exact diagonalization reveal the orbital character states associated with different Raman loss peaks in Cu $K$-edge resonant inelastic x-ray scattering (RIXS) from ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$. includes electronic orbitals necessary to highlight nonlocal Zhang-Rice singlet, charge transfer, and $d\mathrm{\text{\ensuremath{-}}}d$ excitations, as well apical oxygen $2{p}_{z}$ character. dispersion these excitations is discussed prospects for...
We show that spin S Heisenberg chains with an additional three-body interaction of the form (S(i-1)·S(i))(S(i)·S(i+1))+H.c. possess fully dimerized ground states if ratio to bilinear one is equal 1/[4S(S+1)-2]. This result generalizes Majumdar-Ghosh point J1-J2 chain, which present model reduces for S=1/2. For S=1, we use density matrix renormalization group method transition between Haldane and phases continuous a central charge c=3/2. Finally, such appears naturally in strong-coupling...
We investigated the doping dependence of magnetic excitations in lightly doped cuprate La2-xSrxCuO4 via combined studies resonant inelastic x-ray scattering (RIXS) at Cu L3-edge and theoretical calculations. With increasing doping, magnon dispersion is found to be essentially unchanged, but spectral width broadens weight varies differently different momenta. Near Brillouin zone center, we directly observe bimagnon which possess same energy scale as previously observed by Raman spectroscopy....
We present calculations for resonant inelastic x-ray scattering (RIXS) in edge-shared copper oxide systems, such as ${\mathrm{Li}}_{2}\mathrm{Cu}{\mathrm{O}}_{2}$ and $\mathrm{Cu}\mathrm{Ge}{\mathrm{O}}_{3}$, appropriate hard scattering, the $K$ edge. perform exact diagonalizations of multiband Hubbard model determine energies, orbital character, resonance profiles excitations which can be probed via RIXS. find excellent agreement with recent results on...
Motivated by the lack of an obvious spectroscopic probe to investigate non-conventional order such as quadrupolar orders in spin S>1/2 systems, we present a theoretical approach inelastic light scattering for spin-1 quantum magnets context two-band Hubbard model. In contrast S=1/2 case, where only type local excited state is doubly occupied energy $U$, several states with occupation up 4 electrons are present. As consequence, show that two distinct resonating regimes can be accessed...
We study the interplay between effects of surface anisotropy and dipolar interactions in monodisperse assemblies nanomagnets with oriented anisotropy. derive asymptotic formulas for assembly magnetization, taking into account temperature, applied field, core anisotropy, interparticle interactions. find that is well described by analytical expression magnetization derived here: overall sign product two parameters governing contributions determines whether intrinsic collective terms compete or...
We present measurements of the different quantum path contributions to high-order harmonic emission. Through spatial and spectral filtering, we evidence strong correlation between distributions, which allows us quantify contribution each path. A systematic analysis as a function generating parameters has been done identify conditions for efficient generation selection single show that combining phase matching filtering maximizing selecting short contribution, condition ``clean'' intense...
Starting from the mean-field solution of a spin-orbital model $\mathrm{Li}\mathrm{Ni}{\mathrm{O}}_{2}$, we derive an effective quantum dimer (QDM) that lives on triangular lattice and contains kinetic terms acting four-site plaquettes six-site loops. Using exact diagonalizations Green's function Monte Carlo simulations, show competition between these leads to resonating valence bond (RVB) state for finite range parameters. We also this RVB phase is connected identified in Rokhsar-Kivelson...
We investigate the magnetization dynamics of ferromagnetic nanoparticles in atomistic approach taking account surface anisotropy and spin misalignment it causes. demonstrate that such inhomogeneous configurations induce nutation particle's magnetization. More precisely, addition to ordinary precessional motion with frequency ${f}_{p}\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$, we find net magnetic moment exhibits two more resonance peaks frequencies ${f}_{c}$ ${f}_{n}$ which...
We compute the AC susceptibility of a weakly dipolar-interacting monodisperse assembly magnetic nanoclusters with oriented anisotropy. For this purpose we first relaxation rate in longitudinal field single nanomagnet taking account both dipolar interactions case dilute assemblies and surface then study behavior real imaginary components as functions temperature, frequency, anisotropy inter-particle interactions. find that induces an upward shift temperature at maximum its effects may be...
We investigate the problem of inelastic x-ray scattering in spin-$1∕2$ Heisenberg model on square lattice. first derive a momentum-dependent operator for ${A}_{1g}$ and ${B}_{1g}$ polarization geometries. On basis spin-wave analysis, including magnon-magnon interactions exact diagonalizations, we determine qualitative shape spectra. argue that our results may be relevant to help interpret experiments antiferromagnetic phase cuprates.
We investigate equilibrium properties of an exchange-spring magnetic system constituted a soft layer (e.g., Fe) given thickness on top hard FePt). The magnetization profile $M(z)$ as function the atomic position ranging from bottom to is obtained in two cases with regard layer: (i) case rigid interface (the FePt single layer), analytically exact solution sine-Gordon equation Cauchy's boundary conditions. Additional numerical simulations also confirm this result. Asymptotic expressions show...
Recent scanning tunneling microscopy studies have shown that local nanoscale pairing inhomogeneities are correlated with interstitial oxygen dopants in Bi2Sr2CaCu2O8+δ. Combining electrostatic and cluster calculations, this paper the impact of a dopant on Madelung charge transfer energies, magnetic exchange J, Zhang-Rice mobility interactions lattice is investigated. It found modifications locally increase energy slightly suppress J. further coupling to c-axis phonons strongly modified near...
We address the issue of inter-particle dipolar interactions in context magnetic hyperthermia. More precisely, main question dealt with here is concerned conditions under which specific absorption rate enhanced or reduced by interactions. For this purpose, we propose a theory for calculation AC susceptibility, and thereby rate, monodisperse two-dimensional assembly nanoparticles oriented anisotropy, presence DC field, addition to field. also study competition between both transverse...
We present analytical and numerical evidence for the validity of an effective ${S}_{\mathrm{eff}}=\frac{1}{2}$ approach to description random field generation in $S\ensuremath{\geqslant}1$, especially $S=1$, dipolar spin-glass models with strong uniaxial Ising anisotropy subject weak external magnetic ${B}_{x}$ transverse direction. Explicitly ${B}_{x}$-dependent fields are shown naturally emerge low-energy a microscopic $S=1$ toy model. discuss our results relation recent theoretical...
Motivated by various spin-1/2 compounds like Cs2CuCl4 or κ-(BEDT-TTF)2Cu2(CN)3, we derive a Raman-scattering operator à la Shastry and Shraiman for geometries. For T = 0, the exact spectra are computed Lanczos algorithm finite-size clusters. We perform systematic investigation as function of J2/J1, exchange constant ratio: ranging from J2 well known square-lattice case, to J2/J1 1 isotropic triangular lattice. discuss polarization dependence show how it can be used detect precursors...
We discuss how orbital degeneracy, which is usually removed by a cooperative Jahn–Teller distortion, could under appropriate circumstances lead rather to resonating valence bond spin–orbital liquid. The key points are: (i) the tendency form dimers, already identified in several cases; (ii) mapping onto quantum dimer models, have been shown possess phases on triangular lattice. How this programme can be implemented explained some detail starting from microscopic model of LiNiO2.
We develop an analytical approach for studying the ferromagnetic resonance (FMR) frequency shift due to dipolar interactions and surface effects in two-dimensional arrays of nanomagnets with (effective) uniaxial anisotropy along magnetic field. For this we build a general formalism on basis perturbation theory that applies dilute assemblies but which goes beyond point-dipole approximation as it takes account size shape nanoelements, addition their separation spatial arrangement. The...
In the context of magnetic hyperthermia, several physical parameters are used to optimize heat generation, and these include nanoparticles concentration magnitude frequency external AC field. Here, we extend our previous work by computing nonlinear contributions specific absorption rate, while taking into account (weak) inter-particle dipolar interactions a DC work, latter were shown enhance rate in some geometries setup. We find that cubic correction susceptibility does not modify...