The physics of “flat” electrons

Dr Dumitru Călugăru explores the main strategies for engineering flat band materials, discusses band topology concepts and their relevance to flat band physics, and highlights the role of strong interactions in these materials. Landau’s Fermi liquid theory, a cornerstone of condensed matter physics, explains why electrons in most metallic crystalline solids behave as free fermions with renormalized parameters at low enough temperatures. However, the most exotic phases of quantum matter emerge when this framework breaks down—typically when electron-electron interactions become strong enough to surpass the perturbative regime. Such interactions are naturally enhanced in flat band materials, where suppressed kinetic energy allows electron-electron repulsion to dominate. In this talk, I will explore the main strategies for engineering flat band materials, with an emphasis on conventional crystalline systems while briefly touching on engineered heterostructures. I will also introduce key concepts from band topology in an intuitive manner and discuss their relevance to flat band physics. Finally, I will highlight the role of strong interactions in these materials and survey recent experimental realizations.