A5079959549- Iron-based superconductors research
- Rare-earth and actinide compounds
- Advanced Chemical Physics Studies
- Physics of Superconductivity and Magnetism
- Spectroscopy and Quantum Chemical Studies
- Photochemistry and Electron Transfer Studies
- Electron and X-Ray Spectroscopy Techniques
- X-ray Spectroscopy and Fluorescence Analysis
- Laser-Matter Interactions and Applications
- Corporate Taxation and Avoidance
- Advanced Electron Microscopy Techniques and Applications
- Advanced X-ray Imaging Techniques
- Semiconductor Quantum Structures and Devices
- Intellectual Capital and Performance Analysis
- Mass Spectrometry Techniques and Applications
- Semiconductor materials and interfaces
- Superconductivity in MgB2 and Alloys
- Photonic and Optical Devices
- Magnetic properties of thin films
- Semiconductor materials and devices
- Magnetic and transport properties of perovskites and related materials
- Semiconductor Lasers and Optical Devices
- Fullerene Chemistry and Applications
- biodegradable polymer synthesis and properties
- Atomic and Molecular Physics
Karlsruhe Institute of Technology
2016-2025
SLAC National Accelerator Laboratory
2016-2025
Linac Coherent Light Source
2019-2025
Landesanstalt für Umwelt Baden-Württemberg
2013-2024
Stanford University
2014-2024
Vescent Photonics (United States)
2024
Menlo School
2014-2022
Pulse Biosciences (United States)
2014-2021
Stanford Synchrotron Radiation Lightsource
2021
University of Nebraska–Lincoln
2019-2020
We report the observation of two-dimensional electron systems and enhanced mobilities in Si/${\mathrm{Si}}_{0.5}$${\mathrm{Ge}}_{0.5}$ strained-layer multilayer structures. The built-in strain is measured by phonon Raman spectroscopy. mobility enhancement depends strongly on position doped region within layers. experimental results can be explained a consistent way when carrier confinement Si layer assumed. importance lowering conduction band emphasized.
Significance The BCS-BEC (Bardeen–Cooper–Schrieffer––Bose–Einstein-condensate) cross-over bridges the two important theories of bound particles in a unified picture with ratio attractive interaction to Fermi energy as tuning parameter. A key issue is understand intermediate regime, where new states matter may emerge. Here, we show that FeSe extremely small, resulting this system can be regarded an extraordinary “high-temperature” superconductor located at verge cross-over. Most importantly,...
Improvements in experimental resolution allow this group to elucidate how the electronic nematic transition evolves FeSe. They observe changing Fermi surface, position of lowest energy excitations, as well propensity towards order and its manifestation under strain.
The coupling between superconductivity and othorhombic distortion is studied in vapor-grown FeSe single crystals using high-resolution thermal-expansion measurements. In contrast to the Ba122-based (Ba122) superconductors, we find that does not reduce orthorhombicity below Tc. Instead couples strongly in-plane area, which explains large hydrostatic pressure effects. We discuss our results light of spinnematic scenario argue has many features quite different from typical Fe-based superconductors.
Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these directly. Here, we present simultaneous experimental characterization one-photon and two-photon excitation channels isolated CF3I using gas-phase electron diffraction. In channel, mapped out real-space coherent...
We study superconducting FeSe $({T}_{\mathrm{c}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}9\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ exhibiting the tetragonal-orthorhombic structural transition $({T}_{\mathrm{s}}\phantom{\rule{0.16em}{0ex}}\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}90\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ without any antiferromagnetic ordering, by utilizing angle-resolved photoemission spectroscopy. In detwinned orthorhombic state, energy position of...
In quantum systems, coherent superpositions of electronic states evolve on ultrafast timescales (few femtosecond to attosecond, 1 as = 0.001 fs 10^{-18} s), leading a time dependent charge density. Here we exploit the first attosecond soft x-ray pulses produced by an free-electron laser induce core-hole excitation in nitric oxide. Using additional circularly polarized infrared pulse create clock time-resolve electron dynamics, and demonstrate control motion tuning photon energy pulse....
We have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface deviates significantly from predictions of band-structure calculations and most likely consists one electron hole thin cylinder. carrier density is the order 0.01 carriers/ Fe, an order-of-magnitude smaller than predicted. Effective energies as small 3.6 meV are estimated. These findings call for elaborate theoretical investigations incorporating both electronic correlations orbital ordering.
The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x))2As2 iron-based superconductors is obtained from measurements the elastic shear modulus using a three-point bending setup in capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over whole superconducting dome both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior χφ is, surprisingly, only found not...
Organic chromophores with heteroatoms possess an important excited state relaxation channel from optically allowed {\pi}{\pi}* to a dark n{\pi}*state. We exploit the element and site specificity of soft x-ray absorption spectroscopy selectively follow electronic change during {\pi}{\pi}*/n{\pi}* internal conversion. As hole forms in n orbital conversion, near edge fine structure (NEXAFS) spectrum at heteroatom K-edge exhibits additional resonance. demonstrate concept nucleobase thymine,...
Using resistivity, heat-capacity, thermal-expansion, and susceptibility measurements we study the normal-state behavior of KFe2As2. We find that both Sommerfeld coefficient gamma = 103 mJ mol-1 K-2 Pauli chi 4x10-4 are strongly enhanced, which confirm existence heavy quasiparticles inferred from previous de Haas-van Alphen ARPES experiments. discuss this large enhancement using a Gutzwiller slave-boson mean-field calculation, reveals proximity KFe2As2 to an orbital-selective Mott transition....
Abstract Detailed knowledge of the phase diagram and nature competing magnetic superconducting phases is imperative for a deeper understanding physics iron-based superconductivity. Magnetism in superconductors usually stripe-type spin-density-wave, which breaks tetragonal symmetry lattice, known to compete strongly with Recently, it was found that some systems an additional spin-density-wave transition occurs, restores this symmetry, however, its interaction superconductivity remains...
We perform multi-photon direct laser writing as a function of repetition rate over many orders magnitude and otherwise unchanged experimental conditions. These new data serve basis for investigating the influence different proposed mechanisms involved in photopolymerization: two-photon absorption, photoionization, avalanche ionization heat accumulation. find non-linearities high low rates consistent with initiation processes being involved. The scaling resulting linewidths, however, is...
We report the temperature evolution of detailed electronic band structure in FeSe single-crystals measured by angle-resolved photoemission spectroscopy (ARPES), including degeneracy removal $d_{xz}$ and $d_{yz}$ orbitals at $Γ$/Z M points, orbital-selective hybridization between $d_{xy}$ $d_{xz/yz}$ orbitals. The dependences splittings points are different, indicating that they controlled different order parameters. splitting point is closely related to structural transition attributed...
Electronic and nuclear dynamics in one Because of the complex, ultrafast interplay between electronic degrees freedom, probing both excited states within a single time-resolved experiment is great challenge. Yang et al. used electron diffraction combination with ab initio nonadiabatic molecular simulations to study relaxation isolated pyridine molecules after photoexcitation S 1 state (see Perspective by Domcke Sobolewski). They showed that evolution structural changes can be recorded...
Magnetoresistivity ρ(xx) and Hall resistivity ρ(xy) in ultrahigh magnetic fields up to 88 T are measured down 0.15 K clarify the multiband electronic structure high-quality single crystals of superconducting FeSe. At low temperatures high we observe quantum oscillations both effect, confirming Fermi surface with small volumes. We propose a novel approach identify from magnetotransport measurements sign charge carriers corresponding particular cyclotron orbit compensated metal. The observed...
The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits gives a unified framework quantum bound (superfluid) states interacting fermions. This has been studied in ultracold atomic systems, but is extremely difficult to be realized for electrons solids. Recently, superconducting semimetal FeSe with transition temperature $T_{\rm c}=8.5$ K found deep inside BCS-BEC regime. Here we report experimental...
Abstract Increasing the plasma half‐life is an important goal in development of drug carriers, and can be effectively achieved through attachment polymers, particular poly(ethylene glycol) (PEG). While increased has been suggested to a result decreased overall protein adsorption on hydrophilic surface combination with specific proteins, molecular reasons for success PEG other polymers are still widely unknown. We prepared polyphosphoester‐coated nanocarriers defined hydrophilicity control...
We report measurements of resistance and ac magnetic susceptibility on FeSe single crystals under high pressure up to 27.2 kbar. The structural phase transition is quickly suppressed with pressure, the associated anomaly not seen above $\sim$18 superconducting temperature evolves nonmonotonically showing a minimum at $\sim12$ find another 21.2 K 11.6 This most likely corresponds antiferromagnetic found in $μ$SR [M. Bendele \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 087003 (2010)]....
We report a high-resolution angle-resolved photo-emission spectroscopy study of the evolution electronic structure FeSe1-xSx single crystals. Isovalent S substitution onto Se site constitutes chemical pressure which subtly modifies FeSe at high temperatures and induces suppression tetragonal-symmetry-breaking structural transition temperature from 87K to 58K for x=0.15. With increasing substitution, we find smaller splitting between bands with dyz dxz orbital character weaker anisotropic...
The study of the iron-based superconductor FeSe has blossomed with availability high quality single crystals, obtained through flux/vapor-transport growth techniques below structural transformation temperature its tetragonal phase, T~450 C. Here, we report on variation sample morphology and properties due to small modifications in conditions. A considerable superconducting transition Tc, from 8.8 K 3 K, which cannot be correlated composition, is observed. Instead, point out a clear...