Ferromagnetic quantum criticality and superconductivity in Yb-based heavy-fermion systems

• Applicants: Dr. Manuel Brando; Professor Dr. Cornelius Krellner
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 323240951

Ferromagnetic quantum criticality and the occurrence of unconventional superconductivity are central research topics among strongly correlated electron systems. For heavy-fermion systems with trivalent Yb, this is an experimental challenge, because the number of Yb-based compounds showing these types of phenomena is very limited. This is in stark contrast to the huge number of existing antiferromagnetic Kondo-lattice systems and the established occurrence of superconductivity in Ce-based heavy-fermion materials. One important reason for this imbalance is due to the high-vapor pressure of Yb, which makes the crystal growth of these materials very difficult. The recent discoveries of ferromagnetic quantum criticality in YbNi4P2 and the emergence of superconductivity in YbRh2Si2, under the participation of both proposers, was therefore an essential step forward to experimentally investigate these phenomena in Yb-based heavy-fermion metals.The main objectives of this research proposal are the single crystal growth and the low-temperature characterization of Yb-based heavy-fermion compounds close to a magnetic quantum critical point. We will focus on ferromagnetic quantum criticality as well as the occurrence of superconductivity in the vicinity of the quantum critical point. For this purpose, we will investigate in detail (i) YbNi4P2 and related substitution series, (ii) Yb(RhCo)2Si2 and (iii) YbRh2Si2 single crystals. Several crystal growth techniques will be employed to grow very pure single crystals with low amount of defects and reproducible physical properties, which will be characterized by state-of-the art low-temperature physical measurements.

• DFG Programme: Research Grants