Quantum Critical Correlations & Non-local Interactions

It is commonly known that quantum laws control the behavior of particles at the microscopic level. Remarkably, pure quantum effects can become predominant even on macroscopic scales. In solid state physics, two examples are magnetism and superconductivity, which are phenomena not explainable without quantum mechanics. At the same time, they are both highly relevant for technological applications. Astonishing quantum effects also emerge at quantum phase transitions, which occur at absolute zero temperature. These phase transitions are fundamentally different from those we are used to from our everyday life perception, such as the melting of ice or the evaporation of water by increasing temperature. Quantum phase transitions cannot be induced by thermal effects, but originate entirely from quantum effects, which leads to intriguing phenomena. Experimentally, these are detectable at low temperatures, in the so-called quantum critical regime. Extending the route traced in the first funding period of the QUAST research unit, the present project aims at improving our fundamental understanding of the mechanisms underlying quantum phase transitions in various material classes, both experimentally and theoretically. This requires further developments of cutting-edge techniques to investigate extremely challenging low-temperature regimes, where the hallmarks of quantum phase transitions are mostly visible. At the same time, we will pursue theoretical and experimental work in collaboration with the entire research network of QUAST. This will allow us to better understand the delicate interplay between strong electronic interactions, magnetic properties, and lattice vibrations, which often encode the most fascinating and still unexplained phenomena in contemporary condensed matter physics.