Suggested Themes

• The prospective student will be in charge of setting up probes for versatile high precision experiments. These comprise mostly, electrical- and thermal- transport measurements as well as scanning tunneling spectroscopy. In a bachelor’s thesis the probes will be used to conduct experiments in multi-extreme conditions, down to 77 K (or -196 degree Celsius, the temperature at which air liquefies). During a master’s thesis, the range could be extended down to 5 K (as cold as the deep universe) and high magnetic fields nearly million times the earth's magnetic field. Quantum materials of interest range from unconventional superconductors and quantum magnets to topological materials.

• The candidate will grow single crystals of different interesting materials, for example frustrated magnets, and characterize them by using state-of-the-art X-ray synchrotron facilities at DELTA in Dortmund or PETRA III at DESY, Hamburg as well as lab-based sources. Structural properties like the long range and local atomic order and electronic properties like the valence state of selected atoms of these samples can be investigated. The samples will be prepared by hydrothermal synthesis, and solid state reactions, or the flux method if permits. Depending on the choice of techniques used for preparation and investigation of the samples the topic is suited for a bachelor’s as well as a master’s thesis.

• In this project, the influence of a unique tuning parameter on various transport properties, the uniaxial strain, should be investigated. For that a special experimental cell shall be constructed which allows to vary the strain of a sample during measurements. With this it will be possible to study the transport properties of quantum materials and technologically advanced compounds. Additionally, structural investigations of the materials can be combined using lab or synchrotron based X-ray sources. The topic can be adapted for bachelor as well as master students.

• One-dimensional quantum spin systems exhibit extraordinary thermal transport properties. In particular, perfect heat conductivity is expected in model systems such as the S=1/2 Heisenberg chain. In actual materials which host such spin models, the interaction of the usually exotic spin excitations with the lattice as well as with impurties usually hampers the theoretically expected ideal conduction. The aim of this Bachelor project is to compare and analyse the high-temperature thermal transport of various one-dimensional compounds with respect to the impact of impurities, the lattice, and additional interactions within the spin systems.

• Ultra-clean superconducting Niobium plays an important role as a cavity material in today’s acceleration facilities. Scanning tunneling spectroscopy will be used to study the superconducting properties of Niobium. The aim of this Bachelor or Master project is to obtain insight in the role of impurities for the superconducting properties.