This group aims to study quantum materials using a variety of experimental techniques. Our goal is to elucidate the interaction of correlated phases with each other, with the crystal lattice and with the environment. We will prepare crystalline samples, study their properties, manipulate them and discover new physics and functional properties. We are particularly interested in tunable materials, where small changes of external “tuning” parameters lead to an interesting change of properties.
Unconventional superconductors are materials, where superconductivity is caused by a mechanism different from electron-phonon coupling. In many cases, the mechanism is not even understood and instead the focus of research. There are many unconventional superconductors, including the two classes of high-temperature superconductors, the cuprates and the iron-based materials.
Iron-based superconductors: Iron-based superconductors have many fascinating properties. They combine relatively high superconducting transition temperatures with complex phase diagrams and potential applications. In the (German) review referenced below, we summarized the field for a broad audience. Iron-selenide (FeSe) is a special iron-based superconductors that still poses many questions. For example, it features an intriguing interplay of different phases: superconducting, magnetic and nematic (see the phase diagram below), which we summarized in a topical review.
Eisenbasierte Vielfalt, Anna Böhmer und Andreas Kreyssig, Phys. Unserer Zeit, 48: 70-77 (2017) https://doi.org/10.1002/piuz.201701462
Nematicity, magnetism and superconductivity in FeSe, Anna E. Böhmer and Andreas Kreisel, J. Phys.: Condens. Matter 30 023001 (2018) https://doi.org/10.1088/1361-648X/aa9caa
Various types of magnetism are of interest. For example, we are working on tuneable itinerant antiferromagnetism in the cobalt-based materials (Ca,Sr)Co2As2.