A5089304295- Iron-based superconductors research
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Magnetic properties of thin films
- Magnetic Properties of Alloys
- Superconductivity in MgB2 and Alloys
- Inorganic Chemistry and Materials
- Corporate Taxation and Avoidance
- Crystal Structures and Properties
- High-pressure geophysics and materials
- Crystallization and Solubility Studies
- Advanced Chemical Physics Studies
- Inorganic Fluorides and Related Compounds
- X-ray Diffraction in Crystallography
- Superconducting Materials and Applications
- Intellectual Capital and Performance Analysis
- Topological Materials and Phenomena
- Organic and Molecular Conductors Research
- 2D Materials and Applications
- Heusler alloys: electronic and magnetic properties
- Solid-state spectroscopy and crystallography
- Advanced Materials Characterization Techniques
TU Dresden
2016-2025
Complexity and Topology in Quantum Matter
2020-2025
Max Planck Institute for Solid State Research
2009-2020
Max Planck Society
2009-2012
Leibniz Institute for Solid State and Materials Research
2006-2010
Leibniz Association
2007-2008
Leibniz Institute for Neurobiology
2007
Institute of Physics
2004
National Academy of Sciences of Ukraine
2004
Here we present a combined study of the slightly underdoped novel pnictide superconductor Ba1-xKxFe2As2 by means x-ray powder diffraction, neutron scattering, muon-spin rotation (microSR), and magnetic force microscopy (MFM). Static antiferromagnetic order sets in below T{m} approximately 70 K as inferred from scattering zero-field-microSR data. Transverse-field microSR Tc shows coexistence magnetically ordered nonmagnetic states, which is also confirmed MFM imaging. We explain such...
Using angle-resolved photoemission spectroscopy, we report on the direct observation of energy gap in 2H-NbSe2 caused by charge-density waves (CDW). The opens regions momentum space connected CDW vectors, which implies a nesting mechanism formation. In remarkable analogy with pseudogap cuprates, detected also exists normal state (T>T0) where it breaks Fermi surface into "arcs," is nonmonotonic as function temperature local minimum at transition (T0), and forestalls superconducting excluding...
Using angle-resolved photoemission spectroscopy we demonstrate that a normal-state pseudogap exists above T(N-IC) in one of the most studied two-dimensional charge-density wave (CDW) dichalcogenides 2H-TaSe(2). The initial formation incommensurate CDW is confirmed as being driven by conventional nesting instability, which marked pseudogap. magnitude, character, and anisotropy 2D-CDW bear considerable resemblance to those seen superconducting cuprates.
The precise momentum dependence of the superconducting gap in iron-arsenide superconductor ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ (BKFA) with ${T}_{c}=32\text{ }\text{K}$ was determined from angle-resolved photoemission spectroscopy (ARPES) via fitting distribution quasiparticle density to a model. model incorporates finite lifetime and experimental resolution effects, as well accounts for peculiarities BKFA electronic structure. We have found that value...
Small-angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu${}_{2}$OSeO${}_{3}$. In the absence an external magnetic field, helical spin order with modulation vector $q\ensuremath{\parallel}\ensuremath{\langle}001\ensuremath{\rangle}$ was identified. When field is applied, triple-$q$ structure emerges normal to in A phase just below ordering temperature ${T}_{c}$, which suggests formation triangular lattice skyrmions....
Platelike high-quality NaYbS$_{2}$ rhombohedral single crystals with lateral dimensions of a few mm have been grown and investigated in great detail by bulk methods like magnetization specific heat, but also local probes nuclear magnetic resonance (NMR), electron-spin (ESR), muon-spin relaxation ($\mu$SR), inelastic neutron scattering (INS) over wide field temperature range. Our single-crystal studies clearly evidence strongly anisotropic quasi-2D magnetism an emerging spin-orbit entangled...
We have investigated the magnetic structure in a polycrystalline sample of $B20$-type MnGe by means small-angle neutron scattering. On projected diffraction plane normal to incoming beam, Debye-ring-like pattern appears due random orientation spin helix $q$ vectors ($\ensuremath{\parallel}\ensuremath{\langle}100\ensuremath{\rangle}$). When an external field is applied intense peak with wave vector ($q$) perpendicular observed as hallmark formation skyrmion lattice multiple-$q$ wide...
77Se and 87Rb nuclear magnetic resonance (NMR) experiments on Rb0.74Fe1.6Se2 reveal clearly distinct spectra originating from a majority antiferromagnetic (AF) minority metallic-superconducting (SC) phase. The very narrow NMR line of the SC phase evidences absence Fe vacancies any trace AF order. Rb content is deduced intensity measurements identifying Rb(0.3(1))Fe2Se2 as actual composition fraction. resulting estimate 0.15 electrons/Fe brings this class superconductors 245 family closer to...
The authors unveil topological spin structures composed of skyrmion strings in a cubic centrosymmetric iron oxide that provides the missing experimental link between lattices and rich variety helimagnetic order. This is first observation three-dimensional texture bulk perovskite-type oxide, one most ubiquitous important systems for electronics. study enlarges family textures offers promising route toward design novel skyrmionics.
Here we present a calculation of the temperature-dependent London penetration depth, λ(T), in Ba1-xKxFe2As2 (BKFA) on basis electronic band structure (Zabolotnyy et al 2009 Nature 457 569, Zabolotnyy Physica C 469 448) and momentum-dependent superconducting gap (Evtushinsky Phys. Rev. B 79 054517) extracted from angle-resolved photoemission spectroscopy (ARPES) data. The results are compared to direct measurements λ(T) by muon spin rotation (μSR) (Khasanov Lett. 102 187005). value λ(T=0),...
We study the symmetry of spin excitation spectra in 122-ferropnictide superconductors by comparing results first-principles calculations with inelastic neutron-scattering (INS) measurements on ${\text{BaFe}}_{1.85}{\text{Co}}_{0.15}{\text{As}}_{2}$ and ${\text{BaFe}}_{1.91}{\text{Ni}}_{0.09}{\text{As}}_{2}$ samples that exhibit neither static magnetic phases nor structural phase transitions. In both normal superconducting (SC) states, spectrum lacks three-dimensional ${4}_{2}/m$ screw around...
The full three-dimensional dispersion of the pi bands, Fermi velocities, and effective masses are measured with angle-resolved photoemission spectroscopy compared to first-principles calculations. band structure by density-functional theory underestimates slope bands trigonal warping effect. Including electron-electron correlation on level GW approximation, however, yields remarkable improvement in vicinity level. This demonstrates breakdown independent electron picture semimetallic graphite...
We investigate the magnetic penetration depth lambda in superconducting Ba1-xKxFe2As2 (Tc approximately 32 K) with muon-spin rotation (microSR) and angle-resolved photoemission (ARPES). Using microSR, we find penetration-depth anisotropy gamma lambda=lambda c/lambda ab second-critical-field gammaHc2 to show an opposite T evolution below Tc. This dichotomy resembles situation two-gap superconductor MgB2. A scenario is also suggested by inflection point in-plane around 7 K. The complementarity...
Superconductors are classified by their pairing mechanism and the coupling strength, measured as ratio of energy gap, $2\ensuremath{\Delta}$, to critical temperature, ${T}_{\mathrm{c}}$. We present an extensive comparison $2\ensuremath{\Delta}/{k}_{\mathrm{B}}{T}_{\mathrm{c}}$ ratios among many single- multiband superconductors from simple metals high-${T}_{\mathrm{c}}$ cuprates iron pnictides. Contrary recently suggested universality this in Fe-based superconductors, we find that pnictides...
We have studied the low-energy spin-excitation spectrum of single-crystalline ${\mathrm{Rb}}_{2}{\mathrm{Fe}}_{4}{\mathrm{Se}}_{5}$ superconductor (${T}_{c}=32\text{ }\text{ }\mathrm{K}$) by means inelastic neutron scattering. In superconducting state, we observe a magnetic resonant mode centered at an energy $\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{res}}=14\text{ }\mathrm{meV}$ and (0.5 0.25 0.5) wave vector (unfolded Fe-sublattice notation), which differs from ones characterizing...
We present a neutron-scattering study of the static and dynamic spin correlations in underdoped high-temperature superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.45}$ magnetic fields up to 15 T. The field strongly enhances incommensurate order at low temperatures induces spectral-weight shift magnetic-excitation spectrum. A reconstruction Fermi surface driven by field-enhanced superstructure may thus be responsible for unusual topology revealed recent quantum-oscillation...
By means of high-resolution angle-resolved photoelectron spectroscopy (ARPES), we have studied the fermiology 2H transition metal dichalcogenide polytypes TaSe2, NbSe2 and Cu0.2NbS2. The tight-binding model electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate Lindhard function (bare spin susceptibility), which reflects propensity charge density wave (CDW) instabilities observed in TaSe2 NbSe2. We show that though Fermi surfaces compounds possess...
Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays rich array of low-temperature magnetic ordering phenomena which have been the subject investigation for more than 50 years. Its complex behaviour result competing interactions, with both itinerant and local electrons playing important roles. Investigating this material has proven to be substantial challenge, in particular because appearance 'magnetically hidden order' phase, remained elusive neutron-scattering...
Using high-resolution angle-resolved photoemission spectroscopy we have studied the momentum and photon energy dependence of anomalous high-energy dispersion, termed waterfalls, between Fermi level 1 eV binding in several high-T_{c} superconductors. We observe strong changes dispersion different Brillouin zones a on around 75 eV, which associate with resonant at Cu3p-->3d_{x;{2}-y;{2}} edge. conclude that "waterfall" results from suppression intensity center zone due to matrix element...
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...
Inelastic neutron scattering is employed to study the reciprocal-space structure and dispersion of magnetic excitations in normal superconducting states single-crystalline Rb0.8Fe1.6Se2. We show that recently discovered resonant mode this compound has a quasi-two-dimensional character, similar overdoped iron-pnictide superconductors. Moreover, it rich in-plane dominated by four elliptical peaks, symmetrically surrounding Brillouin zone corner, without sqrt(5) x reconstruction. also present...
Heusler compounds with heavy elements often display noncollinear magnetic structures, which can lead to phenomena such as the topological Hall effect. In this study, we report structural, magnetic, electronic, and transport properties of IrMnGa. X-ray neutron diffraction experiments reveal that compound crystallizes in cubic half-Heusler space group 216 $Y$-type disorder. Manganese occupies two nonequivalent positions, causing frustration preventing long-range order. As a consequence, spin...