A5066341734- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Theoretical and Computational Physics
- Magnetic properties of thin films
- Iron-based superconductors research
- Inorganic Fluorides and Related Compounds
- Magnetism in coordination complexes
- Cell Image Analysis Techniques
- Digital Holography and Microscopy
- Multiferroics and related materials
- Advanced NMR Techniques and Applications
- X-ray Diffraction in Crystallography
- Metal-Organic Frameworks: Synthesis and Applications
- Rare-earth and actinide compounds
- Radio Frequency Integrated Circuit Design
- Crystallography and molecular interactions
- Semiconductor Quantum Structures and Devices
- Semiconductor Lasers and Optical Devices
- Electronic and Structural Properties of Oxides
- Nonlinear Photonic Systems
- Crystallization and Solubility Studies
- Image Processing Techniques and Applications
- Inorganic Chemistry and Materials
- Advanced Fluorescence Microscopy Techniques
École Polytechnique Fédérale de Lausanne
2010-2020
Using high-resolution resonant inelastic x-ray scattering (RIXS), we performed a momentum-resolved study of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr_2CuCl_2O_2. We identify both single-spin-wave feature and multi-magnon continuum, show that X-ray polarization can be used to distinguish these two contributions cross-section. The spin-waves display large (70 meV) dispersion between zone-boundary points ($\pi$,0) ($\pi$/2,$\pi$/2). Employing an extended...
Using low-energy projection of the one-band t-t'-t"-Hubbard model we derive an effective spin-Hamiltonian and its spin-wave expansion to order 1/S. We fit dispersion several parent compounds high-temperature superconducting cuprates: La2CuO4, Sr2CuO2Cl2 Bi2Sr2YCu2O8. Our accurate quantitative determination Hubbard parameters allows prediction comparison experimental results measurable quantities such as staggered moment, double occupancy density, velocity bimagnon excitation spectrum density...
High-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen $K$ edge has been used to study orbital excitations of ${\text{Ca}}_{2}{\text{RuO}}_{4}$ and ${\text{Sr}}_{2}{\text{RuO}}_{4}$. In combination with linear dichroism absorption spectroscopy, ruthenium $4d$-orbital occupation were probed through their hybridization $p$ orbitals. These results are described within a minimal model, taking into account crystal field splitting spin-orbit coupling...
Dropping a Dimension? In most magnetic materials, the exchange interaction causes spins on neighboring sites of crystal lattice to align. absence interactions, dipolar which are highly orientation dependent, also expected be able cause magnetism. Kraemer et al. (p. 1416 ) present evidence for antiferromagnetism in dipolar-coupled material, LiErF 4 . Although three-dimensional system, its critical behavior was more reminiscent two-dimensional material.
We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba2IrO4 (Ba-214), an antiferromagnetic (TN = 230 K) insulator. Ba-214 does not exhibit the rotational distortion of IrO6 octahedra that is present in its sister compound Sr2IrO4 (Sr-214), therefore attractive reference material to study electronic structure layered iridates. find band structures Sr-214 are qualitatively similar, hinting at predominant role spin–orbit...
We present a systematic study of the crystal field interactions in Li$R$F$_4$, $R$ = Gd, Ho, Er, Tm and Yb, family rare-earth magnets. Using detailed inelastic neutron scattering measurements we have been able to quantify transition energies wavefunctions for each system. This allows us quantitatively describe high-temperature susceptibility series materials make predictions based on mean-field approach low-temperature thermal quantum phase transitions. show that coupling between phonon...
The influence of dimensionality on the electronic properties layered perovskite materials remains an outstanding issue. We address it here for ${\text{Sr}}_{3}{\text{Ir}}_{2}{\text{O}}_{7}$, bilayer compound iridate ${\text{Sr}}_{n+1}{\text{Ir}}_{n}{\text{O}}_{3n+1}$ series. By angle-resolved photoemission spectroscopy we show that in this material interlayer coupling is large and intercell is, conversely, negligible. From a detailed mapping splitting, from intensity modulation bonding...
High-temperature superconductivity remains arguably the largest outstanding enigma of condensed matter physics. The discovery iron-based high-temperature superconductors has renewed importance understanding in materials susceptible to magnetic order and fluctuations. Intriguingly they show fluctuations reminiscent superconducting (SC) cuprates, including a 'resonance' an 'hour-glass' shaped dispersion, which provide opportunity new insight coupling between spin superconductivity. Here we...
We study the zero-point and thermal ionic motion in ${\text{La}}_{2}$${\text{CuO}}_{4}$ by means of high-resolution neutron-diffraction experiments. Our results demonstrate anisotropic O and, to a lesser extent, Cu ions, both consistent with structure coupled ${\text{CuO}}_{6}$ octahedra, quantify relative effects contributions motion. By substitution $^{18}\mathrm{O}$, we find that oxygen isotope effect on lattice dimensions is small negative ($\ensuremath{-}0.01%$), while displacement...
Abstract The cell is the basis of all life on earth. Therefore, being capable directly observing and measuring internal parts a living would open wealth possibilities. However, due to limitation light used as biological probe, revealing this structure either strongly limited or requires strong tedious modifications observed cells. State‐of‐the art microscopy techniques rely complicated procedures (risk errors), which require difficult time‐consuming preparations, are invasive cells damaging...
We investigate by resonant inelastic x-ray scattering the magnetic excitations in thin films of tetragonal CuO. identify a spin wave excitation, dispersing on two cupratelike antiferromagnetic sublattices. Its energy at boundary Brillouin zone (220 meV), is significantly lower than typical values $(E\ensuremath{\sim}300$ meV) found two-dimensional cuprates. A expansion starting from an extended Hubbard model suggests possible scenarios for this lowering.
We present the experimental phase diagram of LiHo$_x$Er$_{1-x}$F$_4$, a dilution series dipolar-coupled model magnets.The was determined using combination AC susceptibility and neutron scattering. Three unique phases in addition to Ising ferromagnet LiHoF$_4$ XY anti-ferromagnet LiErF$_4$ have been identified. Below $x=0.86$ an embedded spin-glass is observed, where exists within ferromagnetic structure. $x=0.57$ observed consisting frozen needle-like clusters. For $x \sim 0.3 - 0.1$...
The novel iridate Ba8Al2IrO14 was prepared as single crystals by self-flux method, thereby providing a rare example of an all-Ir(VI) compound that can be synthesized under ambient pressure conditions. preparation all-Ir(6+) without using traditional high-pressure techniques has to our knowledge previously only been reported in Nd2K2IrO7 and Sm2K2IrO7. monoclinic crystal structure (space group C2/m, No.12) is stable down 90 K contains layers IrO6 octahedra separated Ba AlO4 tetrahedra....
We present a systematic study of the phase diagram ${\mathrm{LiHo}}_{x}{\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{F}}_{4}$ ($0.25\ensuremath{\le}x\ensuremath{\le}1$) Ising ferromagnets obtained from neutron scattering measurements and mean-field calculations. show that while thermal transition decreases linearly with dilution, as predicted by theory, critical transverse field at quantum point is suppressed much faster. This behavior related to competition between off-diagonal dipolar coupling...
We present a study of the model spin-glass ${\mathrm{LiHo}}_{0.5}{\mathrm{Er}}_{0.5}{\mathrm{F}}_{4}$ using simultaneous ac susceptibility, magnetization, and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when field is applied crystallographic $c$ axis. Furthermore, avalanchelike relaxation observed in static after ramping from zero-field-cooled state up to 200--300 Oe....
The first part of this thesis presents the theoretical study an anomaly unknown origin in excitation spectrum Quantumspin-1/2 Heisenberg Square lattice Anti-Ferromagnet. manifests itself Inelastic Neutron Scattering data for short wavelength/high energy excitations. Instead expected sharp semi-classical harmonic modes, a broad continuum emerges suggesting possibility fractionalized A framework based on Gutzwiller projection is developed and allows to link observed unbound fractional...
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We investigate the spin-$\frac{1}{2}$ Heisenberg model on a rectangular lattice, using Gutzwiller projected variational wave function known as staggered flux state. Using Monte Carlo techniques, parameters and instantaneous spin-spin correlation for different coupling anisotropies $\ensuremath{\gamma}={J}_{y}/{J}_{x}$ are calculated. observe gradual evolution of ground state energy towards value which is very close to one-dimensional (1D) estimate provided by Bethe ansatz good agreement...