Art-Gallery
Thin magnetic film with chiral bobber
Shown is a thin magnetic film with a chiral bobber at each surface. At the tip of the bobber is the so-called Bloch point, where the magnetic field is strongly non-collinear. Our study showed, that the Hall conductivity grows linearly with the distance between the two Bloch points.
Fermi surface of iron
A cut in the Fermi surface of iron measured in PGI-6 by angle-resolved photoemission spectroscopy (ARPES) is compared to the results of a GW calculation. The GW approximation includes renormalization effects due to electron-electron scattering. The experimental results were measured using a photon energy of 70 eV. Whereas the main parts of the figures show results of 40 monolayers (ML) of iron, the insets highlighted in red correspond to 20 ML. In all cases, quantum-well states due to quantum confinement are observed, which are very well reproduced by our GW calculation.
Electronic states of a topological insulator
The figure shows a 3-dimensional representation of the surface states of a topological insulator. They form a so-called Dirac cone (red). The surface states connect to the bulk continuum (blue) via surface resonances (yellow). This calculation corresponds to a 15-quintuple layer slab of Sb2Te3. The theoretical method used includes renormalization effects due to electron-electron scattering within the GW approximation.
Band structure of antimony telluride
Calculated band structure of a 100-quintuple layer slab of Sb2Te3 compared to a spectrum measured by angle-resolved photoemission spectroscopy (ARPES) (experiment performed at PGI-6). The colour encodes the degree of localization of the states on the outermost layer of the slab, with white and yellow for surface states and surface resonances and red for bulk states. The calculation was performed with the GW approximation that includes renormalization effects due to electron-electron scattering.
Renormalized spin susceptibility for nickel
Imaginary part of the renormalized spin susceptibility for fcc Ni as a function of momentum and frequency, obtained from a series of first-principles Bethe-Salpeter calculations. The quadratic spin-wave dispersion is clearly visible. The high resolution of the picture reveals strong mixing of collective and single-particle (Stoner) excitations, which can lead to energy gaps in the spin-wave branch (see inset).
Electron-magnon scattering in iron
The colour-coded plot shows the effect of the electron-magnon scattering on the DFT mean-field band structure (red lines). The calculation relies on first-principles many-body perturbation theory using a k-dependent self-energy developed in Jülich (so-called GT approximation). The effect is strongest in the spin-up channel (a), where the renormalization leads to a complete loss of quasiparticle character in a wide energy range. In the spin-down
channel (b), the GT renormalization gives rise to the formation of a kink structure. This structure was subsequently observed in photoemission experiments carried out at PGI-6 (red symbols).
Néel State
Shown is a periodic Néel state. This is a two-dimensional non-collinear 1200 structure of co-planar spins forming angles between nearest neighbors. A unit cell shown in red contains 3 atoms. The total magnetization M in the unit cell is zero. In this picture, the spins are oriented in the surface plane. The orientation of the spin with respect to the lattice is determined by the spin-orbit interaction.
Spin-Spiral State: (or spin-density wave).
Shown are several spin-spiral states as function of the wave-vector pointing from left to right. The upper two spin-configurations show transversal spin-spiral states. The second spin-configurations of the transversal and longitudinal spin-spiral state show the special case of Theta = 180 Deg.
Spin-Polarized Scanning
Spin-Polarized Scanning Tunneling Microscopy Image of a 2D-Antiferromagnetic Monolayer Film. Direct observation of the two-dimensional atomic scale antiferromagnetic structure of a monolayer magnetic film by spin-polarized scanning tunneling microscopy (SP-STM). All atoms of the monolayer film (red and green) are of the same chemical species (Mn) and differ only by the orientation of their magnetic moment. Using a magnetic probe tip it is possible to measure an SP-STM image (see the height profile).
Fermi surface of tungsten
Shown is the Fermi surface of tungsten in the First Brillouin zone, with the spin-mixing parameter in a color-code. In the presence of spin-orbit coupling, the electronic states are not of pure but of mixed spin character. Points of full spin mixing (value of 0.5) are called 'spin hot spots' (red regions in the picture). The direction of the spin-quantization axis is illustrated by the red arrow. For the phenomenon of spin-relaxation in spin-transport processes, spin-mixing parameter on the Fermi surface is of fundamental importance.
Nono-skyrmionic magnetic structure
Nono-skyrmionic magnetic structure which is found theoretically and validated experimentally for a monolayer of Iron on Iridium (111)
Distribution of the Berry curvature in graphene doped with W atoms
Shown is the distribution of the Berry curvature of graphene doped with tungsten adatoms in a 4x4 superlattice geometry in the reciprocal space. The emergence of the non-zero Berry curvature, which plays a role of a magnetic field in reciprocal space, leads to the occurrence of the quantum anomalous Hall effect in the system - phenomenon, which is being currently intensively researched and sought for experimentally in the field of Chern and topological insulators.
Side-jump scattering in bcc iron
Shown is the distribution of the side-jump scattering contribution to the transverse anomalous Hall conductivity in bcc iron over the "Fermi sphere". In ferromagnets, the side-jump contribution to the scattering-independent transverse conductivity can be as large as the intrinsic, Berry phase driven contribution.
Vacancies in crystalline phase-change materials
Density Functional Theory study of role of vacancies on the electronic structure in crystalline phase-change materials employing the recently developed KKRnano method on the BlueGene/P supercomputer JUGENE using a cubic supercell of 4096 atoms containing Ge512VAC512Sb1024Te2048. The figure displays the atomically resolved spatial distribution of local density of states (LDOS). In the left lower part the chemical information, in the upper right part the value of the LDOS is displayed. Here, large (small) radii of the spheres correspond to high (low) DOS values. For both parts of the plot Ge, Vac, Sb, and Te are shown in white, transparent, light blue, and dark blue, respectively.
Cavities in amorphous tellurium
Amorphous Te crystallizes spontaneously at room temperature, and its structure is still unknown experimentally. Simulations show that there is much empty space surrounding the Te atoms (orange).
Rapid phase change in amorphous Ag/In/Sb/Te alloy
Laser irradiation or heating of the amorphous phase (left) cause the atoms to move. Finally, the central atom with three short (red) bonds and three long bonds (dashed) crosses the centre of the octahedron, interchanging a short and a long bond. Green arrow: resultant vector of short bonds. An avalanche of such processes leads to the crystal form (right).
(a) Crystalline and (b) amorphous Ge_2Sb_2Te_5
Simulation of 460 atoms and 52 vacancies in GST. Red: Ge, blue: Sb, yellow: Te, blue: cavities. Just one cavity is shown in the amorphous state. The structures look very different, but "ABAB squares" (A: Sb, Ge; B: Te) are very common in both.
Blu-ray Disc phase change material
The amorphous structure of GST-8,2,11 (a Blu-ray Disc phase change material) seems chaotic, but close inspection shows important regularities, such as the 16-atom column shown here (Red: Ge, yellow: Te, blue: Sb).
Magnon dispersion of tetragonal FeCo
This image shows the magnon dispersion (acoustic branch) of the B2-type tetragonal FeCo compound along high-symmetry lines in the Brillouin zone. The broadening of the magnon dispersion with increasing energy is due to coupling to single-particle Stoner excitations.
Spin hot loops in hcp rhenium
The image shows the Fermi surface of hcp rhenium in the First Brillouin zone, with the spin-mixing parameter in a color-code. In the presence of spin-orbit coupling, the electronic states are not of pure but of mixed spin character. For electron-spins polarized along the ab-plane of the hcp-structure, so called 'spin hot loops' (lines of full spin-mixed character, shown in red in the picture) emerge close to the hexagonal face of the Brillouin zone boundary. The spin hot loops vanish for electrons which are spin-polarized along the c-axis of the hcp crystal (not shown) and are therefore a source of giant anisotropy of the spin-mixing parameter in hcp rhenium. For the phenomenon of spin-relaxation in spin-transport processes, the spin-mixing parameter on the Fermi surface is of fundamental importance.