Quantum oscillations in a doped Mott insulator beyond Onsager's relation

The Fermi surface --- the manifold of gapless excitations forming due to Pauli's famous exclusion principle--- determines all electronic properties of metals. In 1952 Lars Onsager discovered how to measure a Fermi surface by studying the response of a metallic material as a function of an applied magnetic field. In fact, observables like electrical resistivity or the magnetization oscillate as a function of inverse field. Onsager's relation forms the basis for our understanding of electronic properties of metals and is used in many experimental labs around the world. Here, the authors find that, in the presence of strong interactions between electrons, Onsager's relation can be violated and they provide the first rigorous calculations of this effect. In general, solving for the emergent Landau levels of a strongly interacting material in a magnetic field is a hard problem. The methodological progress made here is enabled by concentrating on an exactly soluble model with infinite-range interactions. This research establishes the importance of inter Landau level interactions for understanding correlated materials in magnetic fields.