DMFT-QE Symposium: January 13th

Talk 1:

Hundness in twisted bilayer graphene: correlated gaps and pairing

Seung-Sup Lee, Seoul National University

We characterize gap-opening mechanisms in the topological heavy fermion (THF) model of magic-angle twisted bilayer graphene (MATBG), with and without electron-phonon coupling, using dynamical mean-field theory (DMFT) with the numerical renormalization group (NRG) impurity solver. In the presence of symmetry breaking associated with valley-orbital ordering (time-reversalsymmetric or Kramers intervalley coherent, or valley polarized), spin anti-Hund and orbital-angularmomentum Hund couplings, induced by the dynamical Jahn–Teller effect, result in a robust pseudogap at filling 2 ≲ |ν| ≲ 2.5. We also find that Hundness enhances the pairing susceptibilities for 1.6 ≲ |ν| ≲ 2.8, which might be a precursor to the superconducting phases neighboring |ν| = 2.

Talk 2:

Heavy fermions vs doped Mott physics in heterogeneous Ta-dichalcogenide bilayers

Roser Valenti, Professor of Theoretical Physics, Goethe University Frankfurt

Controlling and understanding electron correlations in quantum matter is one of the most challenging tasks in materials engineering. In recent years a plethora of new correlated states have been observed by stacking, twisting and straining two-dimensional van der Waals materials of different kind. In Ta-dichalcogenide heterostructures made of a good metallic “1H”- and a Mott insulating “1T”-layer, recent reports have evidenced a cross-breed itinerant and localized nature of the electronic excitations, similar to what is typically found in heavy fermion systems. Here, we will put forward a new interpretation based on combined first-principles with dynamical mean field theory calculations that place Ta-based heterolayers closer to a doped Mott insulator than to a heavy fermion scenario. We will discuss the consequences of our findings in the context of recent STM experiments.