A5089407096- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Rare-earth and actinide compounds
- Advancements in Battery Materials
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Multiferroics and related materials
- Magnetism in coordination complexes
- Carbon Nanotubes in Composites
- Advanced Battery Materials and Technologies
- Supercapacitor Materials and Fabrication
- Transition Metal Oxide Nanomaterials
- Graphene research and applications
- Lanthanide and Transition Metal Complexes
- Corporate Taxation and Avoidance
- Magnetic properties of thin films
- Crystal Structures and Properties
- Diamond and Carbon-based Materials Research
- Theoretical and Computational Physics
- 2D Materials and Applications
- Electron Spin Resonance Studies
- Magnetic Properties of Alloys
- Graphene and Nanomaterials Applications
Heidelberg University
2016-2025
Kirchhoff (Germany)
2016-2025
Centre of Excellence for Advanced Materials
2016-2020
Heidelberg (Poland)
2016-2020
Heidelberg University
2014
Leibniz Institute for Solid State and Materials Research
2004-2012
Leibniz Association
2004-2010
Lomonosov Moscow State University
2007-2009
Leibniz Institute for Neurobiology
2007
University of Szczecin
2007
We present a detailed study on the magnetic order in undoped mother compound LaFeAsO of recently discovered Fe-based superconductor LaFeAsO1-xFx. In particular, we local probe measurements properties by means 57Fe Mössbauer spectroscopy and muon-spin relaxation zero external field along with magnetization resistivity studies. These experiments prove commensurate static strongly reduced ordered moment 0.25(5)muB at iron site below T(N)=138 K, well separated from structural phase transition...
We have performed 75As nuclear magnetic resonance measurements on aligned powders of the new LaFeAsO0.9F0.1 superconductor. In normal state, we find a strong temperature dependence spin shift and Korringa behavior lattice relaxation rate. superconducting evidence for line nodes in gap spin-singlet pairing. Our reveal anisotropy rate, which suggests that vortices contribute to rate when field is parallel c axis but not perpendicular direction.
We present new x-ray and neutron-scattering measurements of stripe order in ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\text{CuO}}_{4}$, along with low-field susceptibility, thermal conductivity, specific-heat data. compare these previously reported results for resistivity thermopower. Temperature-dependent features indicating transitions (or crossovers) are correlated among the various experimental quantities. Taking into account recent spectroscopic studies, we argue that most likely...
We present zero field and transverse muon spin relaxation experiments on the recently discovered Fe-based superconductor LaFeAsO1-xFx (x=0.075 x=0.1). The temperature dependence of deduced superfluid density is consistent with a BCS s-wave or dirty d-wave gap function, while strongly evidences unconventional superconductivity. obtain in-plane penetration depth lambda ab(0)=254(2) nm for x=0.1 ab(0)=364(8) x=0.075. Further evidence superconductivity provided by ratio Tc versus density, which...
From thermodynamics, local spin density approximation+Hubbard U studies and exact diagonalizations of a five-band Hubbard model on CuO2 stripes we find that Li2ZrCuO4 (Li2CuZrO4 in traditional notation) is close to ferromagnetic critical point. Analyzing its susceptibility chi(T) specific heat cp(T,H) within Heisenberg model, show the ratio 2nd 1st neighbor exchange integrals alpha=-J2/J1 approximately 0.3 value alphac=1/4. Comparing with related chain cuprates explain rather strong field...
Fluoroalkylsilanes (FAS) prove to be an interesting water-repellent coating for the recently discussed "superhydrophobic surfaces". The FAS investigated here form a self-assembled monolayer when brought into contact with surface. They arrange at high degree of orientation their molecular axis perpendicular substrate film stability and thickness were observed using X-ray photoelectron spectroscopy. molecules was polarization-dependent absorption near edge spectroscopy (XANES). Furthermore...
We report zero-field muon spin relaxation $(\ensuremath{\mu}\text{SR})$ measurements on $R\text{FeAsO}$ with $R=\text{La}$, Ce, Pr, and Sm. study the interaction of FeAs $R$ (rare-earth) electronic systems in nonsuperconducting magnetically ordered parent compounds $R{\text{FeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ superconductors via a detailed comparison local hyperfine fields at site available M\"ossbauer spectroscopy neutron-scattering data. These studies provide microscopic evidence...
We present the first comprehensive derivation of intrinsic electronic phase diagram iron-oxypnictide superconductors in normal state based on analysis electrical resistivity ρ both LaFeAsO1- xFx and SmF eAsO1- for a wide range doping. Our data give clear-cut evidence unusual normal-state properties these new materials. In particular, emergence superconductivity at low doping levels is accompanied by distinct anomalous transport behavior which reminiscent spin-density wave (SDW) signature...
We have performed inelastic neutron scattering on the near ideal spin-ladder compound La4Sr10Cu24O41 as a starting point for investigating doped ladders and their tendency toward superconductivity. A key feature was separation of one-triplon two-triplon scattering. Two-triplon is observed quantitatively first time so access realized to important strong magnetic quantum fluctuations. The spin gap found be 26.4+/-0.3 meV. data are successfully modeled using continuous unitary transformation...
Due to their extraordinary physical and chemical properties carbon nanotubes reveal promising potential as biomedical agents for heating, temperature sensoring drug delivery on the cellular level. Filling with tailored materials realises nanoscaled containers in which active content is encapsulated by a protecting shell. We describe different synthesis routes show structural magnetic of nanotubes. In particular, filling offers hyperthermia applications while insertion NMR substances allows...
We have studied the interplay of magnetism and superconductivity in ${\text{LaFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ $\text{Ca}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}$. While antiferromagnetic spin-density wave formation is suppressed evolves, all samples show a doping-independent strong increase normal-state susceptibility upon heating which appears general feature iron pnictides. The data provide evidence for robust local correlations persisting even...
We report the structure and magnetism of PrFeAsO, one parent phases Fe-As family superconductors, as measured by neutron powder diffraction. In common with other REFeAsO materials, a tetragonal-orthorhombic phase transition is found on cooling below 136 K striped Fe $k=(1,0,1)$ detected $\ensuremath{\sim}85\text{ }\text{K}$. Our magnetic order-parameter measurements show that ordered moment along $a$ axis reaches maximum at $\ensuremath{\sim}40\text{ }\text{K}$, which an anomalous expansion...
The use of SiO2 as a catalyst for graphitic nanostructures, such carbon nanotubes and graphene, is new rapidly developing system. A key question whether carbide phases form in the reaction. We show formation SiC from nanoparticles synthesis nanostructures via chemical vapor deposition (CVD) at 900 °C. Our findings point to carbothermal reduction CVD inclusion triethyl borate apparently accelerates process leads improved yields. study helps better understand growth mechanisms play nanotube...
Using the spin switch design F1/F2/S theoretically proposed by Oh et al., [Appl. Phys. Lett. 71, 2376 (1997)], that comprises a ferromagnetic bilayer as component, and an ordinary superconductor second interface we have realized full effect for superconducting current. An experimental realization of this construction was achieved CoOx/Fe1/Cu/Fe2/In multilayer.
High-resolution and high-flux neutron as well x-ray powder-diffraction experiments were performed on the oxypnictide series ${\text{LaO}}_{1\ensuremath{-}x}{\text{F}}_{x}\text{FeAs}$ with $0\ensuremath{\le}x\ensuremath{\le}0.15$ in order to study crystal magnetic structure. The symmetry of undoped compound corresponds those reported for $RE\text{OFeAs}$ (with $RE$ a rare earth) $A{\text{Fe}}_{2}{\text{As}}_{2}(A=\text{Ba},\text{Sr})$ materials. We find an ordered moment $0.63(1)\text{...
Hierarchical C@MoS<sub>2</sub>@C hollow spheres with active MoS<sub>2</sub> nanosheets being sandwiched by carbon layers have been produced using a modified template method.
We have measured specific heat, magnetization, and electrical transport properties of ${\mathrm{La}}_{0.875}{\mathrm{Sr}}_{0.125}\ensuremath{-}{\mathrm{MnO}}_{3}$ single crystals in magnetic fields up to 14 T. In addition a ferromagnetic transition two structural phase transitions are observed with one the latter associated charge ordering. The low temperature ordered state is found be stabilized by an applied field, what cannot understood within scope double exchange mechanism, but only...
We report upper critical field Bc2(T) data for disordered (arsenic-deficient) LaO0.9F0.1FeAs1-delta in a wide temperature and magnetic range up to 47 T. Because of the large linear slope Bc2 approximately -5.4 -6.6 T/K near Tc 28.5 K, T dependence in-plane shows flattening 23 K above 30 which points Pauli-limited behavior with Bc2(0) 63-68 Our results are discussed terms disorder effects within [corrected] unconventional superconducting pairings.
The valence states of transition metals were studied by measuring the x-ray absorption spectra at both $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}{L}_{2,3}$ and $\mathrm{Co}\phantom{\rule{0.2em}{0ex}}{L}_{2,3}$ edges partially $B$-site-disordered perovskite $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_{3}$. By comparison with analogous in various Co- Mn-based compounds, divalent state Co ions tetravalent Mn established to ${\mathrm{Mn}}^{4+}∕{\mathrm{Co}}^{2+}$ charge ordering...
We report superconducting (SC) properties of stoichiometric LiFeAs (Tc = 17 K) studied by small-angle neutron scattering (SANS) and angle-resolved photoemission (ARPES). Although the vortex lattice exhibits no long-range order, well-defined SANS rocking curves indicate better ordering than in chemically doped 122-compounds. The London penetration depth 210 nm, determined from magnetic field dependence form factor, is compared to that calculated ARPES band structure with adjustable...