The aim of this project is the single crystal growth and characterization of ternary intermetallic compounds to study collective phenomena resulting from a strong coupling of electrons to phonons. To this end, we will focus on materials with phase transitions where both lattice- and electronic degrees of freedom are involved, as e.g. for the valence transition in Eu-based materials. We will perform a systematic search for novel materials with this type of transition. We are particularly interested in the possibility to tune this transition, either by substitution or pressure, to lower temperatures where we expect to find novel emergent phenomena.
The proposal aims at an electron spectroscopic investigation of RE-based intermetallic compounds (RE = rare-earth) in the vicinity of phase transitions from magnetically ordered to non-ordered states. We focus on RET2M2 compounds crystallizing in the tetragonal layered ThCr2Si2 structure, which can be prepared in form of large, high-quality single-crystalline samples, which can be easily cleaved and handled under ultra-high vacuum conditions allowing to prepare chemically and structurally well-defined surfaces. The project comprises (i) the growth of these crystals and the characterization of their structural and magnetic properties, (ii) their spectroscopic investigation by means of spin- and angle-resolved photoelectron spectroscopy (ARPES) in the UV and soft X-ray range as well as resonant inelastic X-ray scattering (RIXS), and (iii) band structure calculations for the bulk and slab-calculations for the near surface region, complimented by theoretical modeling.
We are interested in Yb-based materials with strongly correlated 4f-electrons. Here, we focus on compounds in the vicinity of quantum critical points to explore the rich phase diagrams including heavy fermion superconductivity, spin liquid and other exotic ground states induced by pressure, doping or magnetic field. In this respect, materials without inversion symmetry, with ferromagnetic correlations and/or layered crystal structure can be challenging candidates to look at. The present focus is on the ferromagnetic YbNi4P2 as well as certain substitution series of the prototypical YbRh2Si2. These type of materials are then study through a numbe of collaborations e.g. in the consortium Fermi-NESt.
The focus of this project lies on the synthesis of high-quality samples of Fe-pnictide and related superconductors, and the achievement of a detailed understanding of their structural, magnetic and superconducting properties. Special emphasis is presently on the so called 1111-type materials, as for these materials the crystal growth is still a big challenge.
The aim of this project is the single crystal growth and characterization of Cu-based quantum spin systems, which serve as model systems to study quantum many-body effects. One important aspect is the role of magnetic frustration, which is closely connected to the geometric arrangement of the Cu2+ spins in the different structure types. Furthermore, we are aiming to prepare materials which are tunable between different magnetic ground states by either substitution or magnetic field. We presently work on three different material classes: (A) Cs2CuCl4-xBrx (B) Ba1-xSrxCuSi2O6 and (C) AxCu4−x(OH)6Cl2.
In recent years, organic semiconductors were strongly investigated due to their huge potential for technical applications, like organic light emitting diodes, organic solar cells, and organic transistors. The modification of the electronic band structure by intercalating organic molecular compounds has been extensively studied in the search for novel physical properties, such as metallic behavior and superconductivity. In this project we grow organic molecular crystals utilizing vapor phase transport and investigate the process of charge transfer in these materials.