Theoretical Physics - From Outer Space to Plasma The physics of “flat” electrons
May 7, 2025
Dumitru Călugăru, a research fellow at Oxford, dives into the fascinating world of flat band materials. He explains how engineering these materials can unlock exotic phases of quantum matter. The conversation covers the importance of band topology and how strong electron interactions can change the behavior of electrons in unique ways. He also touches on the historical context of Landau’s Fermi liquid theory and discusses experimental breakthroughs that illuminate the potential of flat bands in superconductivity.
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Dominance of Interactions in Flat Bands
- In flat bands, kinetic energy is negligible and electron interactions dominate, reversing usual perturbation theory.
- The many-body problem in flat bands requires non-perturbative approaches.
Twisted Bilayer Graphene Phenomena
- Twisted bilayer graphene at the magic angle hosts nearly flat bands that exhibit correlated insulators and superconductivity.
- Temperature increases can sometimes promote ordering, an unusual Pomeranchuk-like effect.
Flat Bands Need Topology Too
- The Hubbard model shows that a flat band with no hopping leads to isolated sites without emergent behavior.
- Flatness alone does not guarantee exotic physics without additional structure like topology.