Research Highlights

Research Highlights

<div style="text-align: justify;">x-ray spectroscopy is an extremely useful and versatile tool for investigating the electronic structure of bulk and thin film materials of <em>3d</em>, <em>4d</em> transition metal and rare earth compounds. The group uses x-ray absorption spectroscopy (XAS) with linear (XLD) and circular polarized light (XMCD), resonant x-ray diffraction (RXD), resonant (RIXS) and nonresonant inelastic x-ray scattering (NIXS), plus angle resolved (ARPES) and hard x-ray photo emission spectroscopy (HAXPES).</div>

Charge-Spin-Orbital degrees of freedom and x-ray spectroscopies

x-ray spectroscopy is an extremely useful and versatile tool for investigating the electronic structure of bulk and thin film materials of 3d, 4d transition metal and rare earth compounds. The group uses x-ray absorption spectroscopy (XAS) with linear (XLD) and circular polarized light (XMCD), resonant x-ray diffraction (RXD), resonant (RIXS) and nonresonant inelastic x-ray scattering (NIXS), plus angle resolved (ARPES) and hard x-ray photo emission spectroscopy (HAXPES).
<div style="text-align: justify;">Hour-glass magnetic excitation spectra are a universal property of copper oxide based high-temperature superconductors. We studied isostructural but insulating cobalt oxides that also exhibit hour-glass magnetic spectra. We were able to observe a new kind of charge and magnetic nano phase separation in this material, thus, unraveling a microscopically split origin of hour-glass spectra on the nano scale.</div>

Hour-glass magnetic excitations

Hour-glass magnetic excitation spectra are a universal property of copper oxide based high-temperature superconductors. We studied isostructural but insulating cobalt oxides that also exhibit hour-glass magnetic spectra. We were able to observe a new kind of charge and magnetic nano phase separation in this material, thus, unraveling a microscopically split origin of hour-glass spectra on the nano scale.
<div style="text-align: justify;">Topological insulators (TI) form a novel state of matter that open up new opportunities to create unique quantum particles. We here present our combined experimental transport, ARPES, STM and theoretical work on a variety of topological non-trivial materials.</div>

Correlated and non-correlated topological insulators

Topological insulators (TI) form a novel state of matter that open up new opportunities to create unique quantum particles. We here present our combined experimental transport, ARPES, STM and theoretical work on a variety of topological non-trivial materials.
<div style="text-align: justify;">We have developed a new method based on ideas obtained both from quantum chemistry and density matrix renormalization group theory for the <em>ab-initio</em> description of the ground-state, excitations, and dynamics of materials with a variable amount of correlation.</div>

New theoretical methods for correlated electron systems

We have developed a new method based on ideas obtained both from quantum chemistry and density matrix renormalization group theory for the ab-initio description of the ground-state, excitations, and dynamics of materials with a variable amount of correlation.
<div style="text-align: justify;">By combining two chalcogenide ions in a crystal structure, novel coordinations of transition metals can be achieved that lead to electronic instabilities. Also, the anisotropy of the crystal structure is directly related to the anionic composition. Chemical reactions in ionic melts and by solid state reactions in closed vessels afford new materials with challenging magnetic, electric, and optic properties.</div>

Composite anionic lattices

By combining two chalcogenide ions in a crystal structure, novel coordinations of transition metals can be achieved that lead to electronic instabilities. Also, the anisotropy of the crystal structure is directly related to the anionic composition. Chemical reactions in ionic melts and by solid state reactions in closed vessels afford new materials with challenging magnetic, electric, and optic properties.
<div style="text-align: justify;">Understanding the microscopic roots of the quantum nature of skyrmions requires a multi-scale approach, spanning the full quantum to classical domain. We achieve this goal for the first time in the spin-½ Mott insulator Cu<sub>2</sub>OSeO<sub>3</sub>, in striking agreement with the experimental data.</div>

Quantum nature of Skyrmions

Understanding the microscopic roots of the quantum nature of skyrmions requires a multi-scale approach, spanning the full quantum to classical domain. We achieve this goal for the first time in the spin-½ Mott insulator Cu2OSeO3, in striking agreement with the experimental data.
<div style="text-align: justify;"><span>A collaborative research between the departments of correlated matter, chemical metal sciences, and the physics of quantum materials in the field of Fe-based chalcogenides resulted in an extensive and widespread insight into the intricate physics of these interesting compounds. In the following we briefly summarize a few important results.</span></div>

Fe-chalcogenide based superconductors

A collaborative research between the departments of correlated matter, chemical metal sciences, and the physics of quantum materials in the field of Fe-based chalcogenides resulted in an extensive and widespread insight into the intricate physics of these interesting compounds. In the following we briefly summarize a few important results.
<div style="text-align: justify;">Strong electronic correlations in solids may result in fascinating, yet often not fully understood phenomena, including unconventional superconductivity and quantum criticality in heavy fermion metals. Detailed experimental and theoretical investigations are performed to gain a more complete comprehension within this emerging field of solid state physics.</div>

Heavy fermion materials

Strong electronic correlations in solids may result in fascinating, yet often not fully understood phenomena, including unconventional superconductivity and quantum criticality in heavy fermion metals. Detailed experimental and theoretical investigations are performed to gain a more complete comprehension within this emerging field of solid state physics.
<div style="text-align: justify;">The physics of the <em>5d</em> transition compounds is driven by the competition of comparable energy scales. At the heart of the group’s research interest is the aspect of band formation versus local physics.  New Os perovskite materials will be synthesized and the orbital configuration (local versus band) will be investigated with XMCD.</div>

Osmates and novel transition metal oxides

The physics of the 5d transition compounds is driven by the competition of comparable energy scales. At the heart of the group’s research interest is the aspect of band formation versus local physics.  New Os perovskite materials will be synthesized and the orbital configuration (local versus band) will be investigated with XMCD.
 
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