DMFT-QE Symposium: March 11

Date & Time

Talk 1:

The unconventional normal state of twisted bilayer graphene

María José Calderón, Instituto de Ciencia de Materiales de Madrid (CSIC)

Twisted bilayer Graphene (TBG) shows a great variety of correlated states such as superconducting, insulating, magnetic or intervalley coherent phases. Among the experimental observations, the cascades in the spectroscopic properties [1] and in the compressibility [2] happen in larger ranges of energy, twist angle and temperature than other effects, pointing to a hierarchy of phenomena. In this talk I will show that the origin of the cascades is associated to the formation of local moments and heavy quasiparticles and not to the symmetry breaking orders [3]. Our results are based on Dynamical Mean Field Theory plus Hartree calculations. We reproduce the cascade flow of spectral weight, the oscillations of the remote band energies, the asymmetric jumps of the inverse compressibility, and the presence of resistive states. We predict a strong momentum differentiation in the incoherent spectral weight associated to the fragile topology of TBG. I will also show how strong correlations impact other measurements that can be performed in order to characterize the unconventional normal state of these moiré systems.

[1] D. Wong et al, Nature 582, 198 (2020); Y. Choi et al, Nature 589, 536 (2021).
[2] U. Zondiner et al, Nature 582, 203 (2020).
[3] A. Datta, A. Camjayi, M.J. Calderón and E. Bascones, Nature Communications 14, 5036 (2023)

Talk 2:

Dynamical correlations and order in twisted bilayer graphene

Gautam Rai, Universität Hamburg

We use dynamical mean-field theory on the topological heavy Fermion model of magic-angle twisted bilayer graphene (TBLG) to investigate the interplay of electronic correlations and long-range order in the non-superconducting phase of this system. Our work [1, 2] identifies three central events in the filling-temperature plane: (i) the formation of local spin and valley isospin moments at around 100K, (ii) the ordering of these local isospin moments at around 10K, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. These three phenomena underpin some of the most puzzling aspects of data from scanning tunneling spectroscopy, transport, and compressibility experiments. In my talk, I will show you what we have learnt about the nature of the emergent insulating and metallic states, the doping- and temperature-induced transitions between them, the so-called cascade transitions in local density and compressibility, and the microscopic mechanism behind the isospin Pomeranchuk effect in TBLG.
[1] arXiv:2309.08529
[2] Phys. Rev. Lett. 131, 166501 (2023)

March 11, 2024

Maria Jose Calderon: The Unconventional Normal State of Twisted Bilayer Graphene

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Gautam Rai: Dynamical Correlations and Order in Twisted Bilayer Graphene

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