A5004935276- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Rare-earth and actinide compounds
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Cold Atom Physics and Bose-Einstein Condensates
- Corporate Taxation and Avoidance
- Superconductivity in MgB2 and Alloys
- Quantum and electron transport phenomena
- Topological Materials and Phenomena
- Magnetic properties of thin films
- Magnetic Properties of Alloys
- Quantum, superfluid, helium dynamics
- Theoretical and Computational Physics
- Quantum many-body systems
- Inorganic Chemistry and Materials
- Intellectual Capital and Performance Analysis
- Multiferroics and related materials
- Magneto-Optical Properties and Applications
- Atomic and Subatomic Physics Research
- Surface and Thin Film Phenomena
- Crystal Structures and Properties
- Inorganic Fluorides and Related Compounds
- Superconducting Materials and Applications
- Mechanical and Optical Resonators
University of Copenhagen
2014-2025
Quantum Devices (United States)
2025
Leipzig University
2016-2023
Helmholtz-Zentrum Berlin für Materialien und Energie
2018
University of Florida
2012-2015
Goethe University Frankfurt
2007-2012
University of Würzburg
2012
A deeper look into iron selenide In the past 10 years, iron-based superconductors have created more puzzles than they helped resolve. Some of most fundamental outstanding questions are how strong interactions and what electron pairing mechanism is. Now two groups made contributions toward resolving these in intriguing compound (FeSe) (see Perspective by Lee). Gerber et al. used photoemission spectroscopy coupled with x-ray diffraction to find that FeSe has a very sizable electron-phonon...
Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with is not obvious. Superconductivity in highly tunable, the superconducting transition temperature, Tc, ranging from 8 K bulk single crystals at ambient pressure to almost 40 under or intercalated systems, even higher...
We discuss the influence on spin-fluctuation pairing theory of orbital selective strong correlation effects in Fe-based superconductors, particularly Fe chalcogenide systems. propose that a key ingredient for an improved itinerant is selectivity, i.e., incorporating reduced coherence quasiparticles occupying specific states. This modifies usual via suppression pair scattering processes involving those less coherent states and results Cooper electrons remaining show this paradigm yields...
Emergent electronic phenomena in iron-based superconductors have been at the forefront of condensed matter physics for more than a decade. Much has learned about origin and intertwined roles ordered phases, including nematicity, magnetism, superconductivity, this fascinating class materials. In recent years, focus centered on peculiar highly unusual properties FeSe its close cousins. This family materials attracted considerable attention due to discovery unexpected superconducting gap...
We report the optical detection of magnons with a broad range wavevectors in magnetic insulator Y3Fe5O12 thin films by proximate nitrogen-vacancy (NV) single-spin sensors. Through multimagnon scattering processes, excited generate fluctuating fields at NV electron spin resonance frequencies, which accelerate relaxation spins. By measuring variation emitted spin-dependent photoluminescence centers, variable up to ∼5 × 107 m–1 can be optically accessed, providing an alternative perspective...
The discovery of superconductivity in infinite-layer nickelates has added a new family materials to the fascinating growing class unconventional superconductors. By incorporating strongly correlated multiorbital nature low-energy electronic degrees freedom, we compute leading superconducting instability from magnetic fluctuations relevant for nickelates. Specifically, by properly including doping dependence Ni d_{x^{2}-y^{2}} and d_{z^{2}} orbitals as well self-doping band, uncover...
Altermagnets feature vanishing net magnetization, similar to antiferromagnets, but exhibit time-reversal symmetry breaking and spin-split band structures. This work constructs minimal models for altermagnetism based on arguments considering two magnetic atoms in the unit cell demonstrates that these can capture key properties of structure altermagnetic spin splitting material candidate RuO${}_{2}$. Notably, have ground states give rise a Berry curvature conductivity linear spin-orbit coupling.
We reconsider the effect of disorder on properties a superconductor characterized by sign-changing order parameter appropriate for Fe-based materials. Within simple two-band model, we calculate simultaneously ${T}_{c}$, change in residual resistivity $\ensuremath{\Delta}{\ensuremath{\rho}}_{0}$, and zero-energy density states, show how these results various types gap structure assumptions regarding impurity scattering. The rate ${T}_{c}$ suppression is shown to vary dramatically according...
We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations problem of interpreting STM data in cuprate superconductors. show that observed images Zn on surface Bi_{2}Sr_{2}CaCu_{2}O_{8} can only be understood by accounting for tails Cu functions, which include significant weight apical O sites neighboring unit cells. This calculation thus puts earlier crude "filter" theories microscopic foundation and solves...
We provide a band structure with low-energy properties consistent recent photoemission and quantum oscillation measurements on FeSe, assuming mean-field-like site- and/or bond-centered ferro-orbital ordering at the structural transition. show how resulting model provides explanation of temperature dependence measured Knight shift spin-relaxation rate. Furthermore, superconducting gap obtained from spin-fluctuation theory exhibits nodes electron pockets, $V$-shaped density states by tunneling...
A growing number of superconducting materials display evidence for spontaneous time-reversal symmetry breaking (TRSB) below their critical transition temperatures. Precisely what this implies the nature ground state such materials, however, is often not straightforward to infer. We review experimental status and survey different theoretical mechanisms generation TRSB in superconductors. In cases where a complex combination two order parameter components realized, defects, dislocations sample...
The spectral distribution of parametrically excited dipole-exchange magnons in an in-plane magnetized epitaxial film yttrium-iron garnet was studied by means frequency- and wavevector-resolved Brillouin light scattering spectroscopy. experiment performed a parallel pumping geometry where exciting microwave magnetic field to the magnetizing field. It found that for both dipolar exchange areas excites lowest volume magnon modes propagating plane perpendicularly magnetization direction. In...
The lack of nesting the electron and hole Fermi-surface sheets in Fe-based superconductor LiFeAs, with a critical temperature 18 K, has led to questions as whether origin superconductivity this material might be different from other superconductors. Both angle-resolved photoemission quasiparticle interference experiments have reported fully gapped superconducting order parameters significant anisotropy. system is also interest because relatively strong correlations seem responsible for...
We study the spin-fluctuation-mediated superconducting pairing gap in a weak-coupling approach to Hubbard model for two-dimensional square lattice paramagnetic state. Performing comprehensive theoretical of phase diagram as function filling, we find that exhibits transitions from $p$-wave at very low electron fillings ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave symmetry close half filling agreement with previous reports. At intermediate levels, different symmetries appear consequence changes...
Motivated by the recent discovery of superconductivity in kagome ${A\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ $(A=\mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$ metals, we perform a theoretical study symmetry-allowed superconducting orders on two-dimensional lattice with focus their response to disorder. We uncover qualitative difference between robustness intraband spin-singlet (even-parity) and spin-triplet (odd-parity) unconventional atomic-scale nonmagnetic Due particular sublattice character electronic...
Brillouin light scattering spectroscopy is a powerful technique for the study of fast magnetization dynamics with both frequency and wavevector resolutions. Here, we report on distinct improvement this spectroscopic toward two-dimensional wide-range selectivity in backward geometry. Spin-wave wavevectors oriented perpendicularly to bias magnetic field are investigated by tilting sample within magnet gap. Wavevectors which parallel applied analyzed turning entire setup, including system. The...
We propose a simple method of calculating inhomogeneous, atomic-scale phenomena in superconductors which makes use the wave function information traditionally discarded construction tight-binding models used Bogoliubov--de Gennes equations. The uses symmetry-based first-principles Wannier functions to visualize effects superconducting pairing on distribution electronic states over atoms within crystal unit cell. Local symmetries lower than global lattice symmetry can thus be exhibited as...
We present a theoretical study of the dynamical spin susceptibility for intriguing Fe-based superconductor FeSe, based on tight-binding model developed to account temperature-dependent band structure in this system. The allows orbital ordering ${d}_{xz}/{d}_{yz}$ channel below structural transition and presents strongly ${C}_{4}$-symmetry-broken Fermi surface at low temperatures which accounts nematic properties material. calculated excitations are peaked wave vector $(\ensuremath{\pi},0)$...
The unconventional superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ has been the subject of enormous interest over more than two decades, but until now form its order parameter not explicitly determined. Since groundbreaking NMR experiments revealed recently that pairs are dominant spin-singlet character, attention focused on time-reversal symmetry breaking linear combinations $s$-, $d$-, and $g$-wave one-dimensional (1D) irreducible representations. However, a state ${d}_{xz}+i{d}_{yz}$...
Spontaneous generation of time-reversal symmetry breaking in unconventional superconductors is currently a topic considerable interest. While chiral superconducting order often assumed to be the source such signatures, they can sometimes also arise from nonmagnetic disorder. Here we perform theoretical study impact dislocations on parameter within microscopic one-band model which, homogeneous case, features either extended $s$-wave, $d$-wave, or $s+id$-wave superconductivity depending...