Quantum criticality in transition-metal oxides and chalcogenides and in frustrated lattices

• Antragsteller: Privatdozent Dr. Norbert Büttgen
• Fachliche Zuordnung: Experimentelle Physik der kondensierten Materie
• Förderung: Förderung von 2007 bis 2014
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 48554140

Quantum criticality will be investigated in metallic and insulating transition-metal oxides andchalcogenides. Concerning metallic systems we will continue our work on LiV2O4 which is thefirst heavy-fermion transition-metal oxide. It has been shown that the pure compound is veryclose to an antiferromagnetic (AFM) quantum critical point (QCP). From detailed NMRstudies in high-purity samples we found experimental evidence for two relaxation channelsbelow 0.5 K, which might indicate the break-up of composite heavy quasiparticles intolocalized spins and "normal band states". This behaviour will be studied in more detail,including measurements in external magnetic fields and in samples with well defined dopinglevels. In addition, we will focus on the large group of copper-ruthenates of the compositionACu3Ru4O12 (A = Na, Ca, Sr, La, Pr, Nd). These systems reveal heavy-fermion (HF) andnon-Fermi liquid (NFL) behaviour and can properly be tuned towards a magnetic QCP, whichcoincides with a metal-to-insulato transition r (MIT). Quantum criticality can be achieved bysubstituting ruthenium by titanium or by doping at the A site. Many open questions are left inthese systems, including the nature of the HF behaviour, intermediate valence, and the originof the MIT. Specifically, the role of the ruthenium and copper d-electrons has not beenclarified unambiguously. The MIT seems to correlate with the appearance of local momentsat the Cu site.

• DFG-Verfahren: Forschungsgruppen
• Teilprojekt zu: FOR 960: Quantum Phase Transitions
• Beteiligte Personen: Privatdozent Dr. Hans-Albrecht Krug von Nidda; Professor Dr. Alois Loidl