Quantum fields and quantum materials at criticality and beyond

The study of phase transitions and critical phenomena has shaped our understanding of nature in a fundamental way and far beyond the realm of classical statistical physics. In fact, this field of study finds many applications, e.g., in the phase diagrams of quantum chromodynamics and novel correlated two-dimensional materials, just to name two prominent examples. In my talk, I will discuss basically three scenarios, in which our standard paradigms with which we typically understand phase transitions and critical phenomena are challenged and novel ideas and concepts are required.

Specifically, I will discuss how the presence of massless Dirac excitations strongly modifies the critical behavior near a quantum critical point of two-dimensional quantum materials. Then, I will show how topological excitations in certain spin models can lead to the disappearance of true critical behavior and replace it by the newly discovered concept of Nordic Walking.

Finally, I will discuss the phenomenon of temperature-resistant order, i.e., a type of Pomeranchuk effect near a very special quantum critical point where order can persist at all temperatures.