Dynamical correlations and order in magic-angle twisted bilayer graphene
- URL: http://arxiv.org/abs/2309.08529v1
- Date: Fri, 15 Sep 2023 16:46:36 GMT
- Title: Dynamical correlations and order in magic-angle twisted bilayer graphene
- Authors: Gautam Rai, Lorenzo Crippa, Dumitru C\u{a}lug\u{a}ru, Haoyu Hu, Luca
de' Medici, Antoine Georges, B. Andrei Bernevig, Roser Valent\'i, Giorgio
Sangiovanni, Tim Wehling
- Abstract summary: We study the emergence of electronic correlations and long-range order in the absence of strain in twisted bilayer graphene.
We explain the nature of emergent insulating and correlated metallic states, as well as transitions between them driven by three central phenomena.
- Score: 0.29022435221103454
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: In magic angle twisted bilayer graphene, transport, thermodynamic and
spectroscopic experiments pinpoint at a competition between distinct low-energy
states with and without electronic order, as well as a competition between
localized and delocalized charge carriers. In this study, we utilize Dynamical
Mean Field Theory (DMFT) on the topological heavy Fermion (THF) model of
twisted bilayer graphene to investigate the emergence of electronic
correlations and long-range order in the absence of strain. We explain the
nature of emergent insulating and correlated metallic states, as well as
transitions between them driven by three central phenomena: (i) the formation
of local spin and valley isospin moments around 100K, (ii) the ordering of the
local isospin moments around 10K, and (iii) a cascadic redistribution of charge
between localized and delocalized electronic states upon doping. At integer
fillings, we find that low energy spectral weight is depleted in the symmetric
phase, while we find insulating states with gaps enhanced by exchange coupling
in the zero-strain ordered phases. Doping away from integer filling results in
distinct metallic states: a "bad metal" above the ordering temperature, where
coherence of the low-energy electronic excitations is suppressed by scattering
off the disordered local moments, and a "good metal" in the ordered states with
coherence of quasiparticles facilitated by isospin order. Upon doping, there is
charge transfer between the localized and delocalized orbitals of the THF model
such that they get periodically filled and emptied in between integer fillings.
This charge reshuffling manifests itself in cascades of doping-induced Lifshitz
transitions, local spectral weight redistributions and periodic variations of
the electronic compressibility ranging from nearly incompressible to negative.
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