A5049028249- Iron-based superconductors research
- Rare-earth and actinide compounds
- Physics of Superconductivity and Magnetism
- Corporate Taxation and Avoidance
- Superconductivity in MgB2 and Alloys
- Quasicrystal Structures and Properties
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Advanced Condensed Matter Physics
- Intermetallics and Advanced Alloy Properties
- Intellectual Capital and Performance Analysis
- Magnetic Properties of Alloys
- Metallurgical and Alloy Processes
- Magnetic and transport properties of perovskites and related materials
- Nuclear materials and radiation effects
- Multiferroics and related materials
- Thermal Expansion and Ionic Conductivity
- Magnesium Alloys: Properties and Applications
- Zeolite Catalysis and Synthesis
- Magnetic properties of thin films
- Boron and Carbon Nanomaterials Research
- Semiconductor materials and devices
- GaN-based semiconductor devices and materials
- High-pressure geophysics and materials
- Aluminum Alloy Microstructure Properties
École Polytechnique Fédérale de Lausanne
2007-2021
ETH Zurich
2006-2016
A.V. Shubnikov Institute of Crystallography
2009
University of Geneva
2008
Frantsevich Institute for Problems in Materials Science
2002-2007
Institute of Crystallography
2007
University of Tübingen
2005
Centre National de la Recherche Scientifique
2005
AGH University of Krakow
2004
National Academy of Sciences of Ukraine
2003
Single crystals of SmFeAsO1−xFy a size up to 120 × 100 µm2 have been grown from NaCl/KCl flux at pressure 30 kbar and temperature 1350–1450 °C using the cubic anvil high-pressure technique. The superconducting transition obtained single varies between 45 53 K. Obtained are characterized by full diamagnetic response in low magnetic fields high critical current density fields. Structural refinement has performed on crystal. Differential thermal analysis investigations 1 bar Ar show...
Iron-chalcogenide single crystals with the nominal composition ${\text{FeSe}}_{0.5}{\text{Te}}_{0.5}$ and a transition temperature of ${T}_{c}\ensuremath{\simeq}14.6\text{ }\text{K}$ were synthesized by Bridgman method. The structural anisotropic superconducting properties those investigated means crystal x-ray neutron powder diffraction, quantum interference device torque magnetometry, muon-spin rotation (\ensuremath{\mu}SR). Room diffraction reveals that 95% volume is same tetragonal...
The in-plane magnetic penetration depth ${\ensuremath{\lambda}}_{ab}$ of the iron selenide superconductor with nominal composition ${\text{FeSe}}_{0.85}$ was studied by means muon-spin rotation. measurements ${\ensuremath{\lambda}}_{ab}^{\ensuremath{-}2}(T)$ are inconsistent a simple isotropic $s$-wave type order parameter but rather in favor two-gap $(s+s)$ and anisotropic symmetries, thus implying that superconducting energy gap contains no nodes.
We report measurements of the in-plane magnetic penetration depth $\ensuremath{\lambda}$ in single crystals ${\text{SmFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{y}$ $(x\ensuremath{\simeq}y\ensuremath{\simeq}0.2)$ with ${T}_{c}\ensuremath{\simeq}44\text{ }\text{K}$. find that at low temperature has an exponential dependence which suggests Fermi surface is fully gapped. The magnitude minimum energy gap, ${\ensuremath{\Delta}}_{1}=1.1\ifmmode\pm\else\textpm\fi{}0.1{k}_{B}{T}_{c}$ $T=0$,...
The superconducting and magnetic properties of Fe$_{y}$Se$_{0.25}$Te$_{0.75}$ single crystals ($0.9\leq y \leq1.1$) were studied by means x-ray diffraction, SQUID magnetometry, muon spin rotation, elastic neutron diffraction. samples with $y<1$ exhibit coexistence bulk superconductivity incommensurate magnetism. order remains for $y\geq 1$, but increasing Fe content is suppressed the correlation length increases. results show that Fe$_{y}$Se$_{1-x}$Te$_{x}$ can be tuned not only varying...
We use femtosecond spectroscopy to investigate the quasiparticle relaxation and low-energy electronic structure in a nearly optimally doped pnictide superconductor with T{c}=49.5 K. Multiple processes are evident, distinct superconducting state recombination dynamics exhibiting T-dependent gap, clear "pseudogaplike" feature an onset above 180 K indicating existence of temperature-independent gap magnitude Delta{PG}=61+/-9 meV T{c}. Both pseudogap components show saturation as function...
Single crystals of the LnFeAsO (Ln1111, Ln = Pr, Nd, and Sm) family with lateral dimensions up to 1 mm were grown from NaAs KAs flux at high pressure. The are good structural quality become superconducting when O is partially substituted by F (PrFeAsO1-xFx NdFeAsO1-xFx) or Fe Co (SmFe1-xCoxAsO). From magnetization measurements, we estimate temperature dependence anisotropy upper critical field current density underdoped PrFeAsO0.7F0.3 crystal Tc 25 K. SmFe1-xCoxAsO maximal 16.3 K for x 0.08...
Single crystals of ${\text{Ba}}_{1\ensuremath{-}x}{\text{Rb}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ with $x=0.05\ensuremath{-}0.1$ have been grown from Sn flux and are bulk superconductors ${T}_{c}$ up to 23 K. The crystal structure was determined by x-ray diffraction analysis, is found be incorporated for $\ensuremath{\sim}9%$ Ba, shifted $\ensuremath{\sim}1.1\text{ }\text{\AA{}}$ away the Ba site toward $({\text{Fe}}_{2}{\text{As}}_{2})$ layers. upper critical field deduced resistance...
We report structural, magnetic, and transport properties of polycrystalline samples single crystals superconducting ${\text{Sm}}_{1\ensuremath{-}x}{\text{Th}}_{x}\text{FeAsO}$ with maximal ${T}_{c}$ above 50 K, prepared under high pressure. Bulk do not undergo a structural phase transition from tetragonal to orthorhombic symmetry at low temperatures. The unit-cell parameters $a$ $c$ shrink Th substitution the fractional atomic coordinate As site ${z}_{\text{As}}$ remains almost unchanged...
We investigate the quasiparticle (QP) relaxation and low-energy electronic structure in undoped SmFeAsO near-optimally doped ${\text{SmFeAsO}}_{0.8}{\text{F}}_{0.2}$ single crystals--exhibiting spin-density wave (SDW) ordering superconductivity, respectively--using pump-probe femtosecond spectroscopy. In crystals a process is observed, showing remarkable critical slowing down of QP dynamics at SDW transition temperature ${T}_{\text{SDW}}\ensuremath{\simeq}125\text{ }\text{K}$....
The interplay between magnetism and superconductivity in LaFeAsO_0.945F_0.055 was studied as a function of hydrostatic pressure up to p~2.4GPa by means muon-spin rotation (\muSR) magnetization measurements. application leads substantial decrease the magnetic ordering temperature T_N reduction phase volume and, at same time, strong increase superconducting transition T_c diamagnetic susceptibility. From sensitive \muSR measurements it can be concluded that areas which coexist sample are...
We probe the local quasiparticles density of states in micron-sized ${\mathrm{SmFeAsO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}$ single crystals by means scanning tunnelling spectroscopy. Spectral features resemble those cuprates, particularly a dip-hump-like structure developed at energies larger than gap that can be ascribed to coupling collective mode, quite likely resonant spin mode. The energy mode revealed our study decreases when pairing strength increases. Our findings support...
We report inelastic x-ray scattering experiments on the lattice dynamics in SmFeAsO and superconducting ${\text{SmFeAsO}}_{0.60}{\text{F}}_{0.35}$ single crystals. Particular attention was paid to dispersions along [100] direction of three optical modes close 23 meV, polarized out FeAs planes. Remarkably, two these are strongly renormalized upon fluorine doping. These results provide significant insight into energy momentum dependence coupling electron system underline importance spin-phonon...
A combination of x-ray diffraction, magnetization, and 75As nuclear magnetic resonance (NMR) experiments were performed on single-crystal EuFe1.9Co0.1As2. The strength the hyperfine interaction between nuclei Eu^(2+) 4f states suggests a strong coupling moments Fe1.9Co0.1As2 layers. Such interlayer may be due to an indirect exchange localized moments, mediated by Fe 3d conduction electrons. Magnetic susceptibility as well 75As-NMR measurements reveal decrease SDW transition temperature T_SDW...
The effect of Li substitution and Li-C co-substitution on the superconducting properties crystal structure ${\text{MgB}}_{2}$ single crystals has been investigated. Hole doping with decreases transition temperature ${T}_{c}$ at a slower rate than that electron C or Al. For co-substituted for Mg B, more rapidly substituted alone. This means holes introduced cannot counterbalance influence electrons doped are not able to prevent decrease. possible explanation is coming from occupy mainly...