Beecroft Building, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU
Dr Lorenzo Crippa, Universität Hamburg
Dumitru Călugăru, dumitru.calugaru@physics.ox.ac.uk
Abstract
Phase Diagram and Spectroscopy of Twisted Bilayer Graphene: Correlations, Order, and Lattice Distorsions
Twisted bilayer graphene (TBG) hosts a remarkably rich set of correlated phases. Currently, a unified theoretical description of its many spectroscopic, thermodynamic, and ordering properties is far from complete. Many of the exotic properties exhibited by this material stem from the duality of localized and itinerant electrons it features. Hence, relevant progress in the theoretical modeling of TBG has been made by employing the toolbox of strongly correlated electron systems, describing the system as a Periodic Anderson Model (PAM) and employing the well established solution technique known as Dynamical Mean-Field Theory (DMFT).
In this talk, I will present the results of our microscopic many-body simulations, which combine dynamical correlation effects with spontaneous flavor symmetry breaking, heterostrain, and lattice relaxation. This modeling framework reveals how these intertwined ingredients cooperatively shape the electronic spectra and phase diagram of TBG, naturally reproducing key experimental observations, from Scanning Tunneling and Quantum Twisting Microscopy to entropy and transport measurements. I will discuss how TBG undergoes doping- and temperature-controlled gap opening transitions associated with interaction-driven symmetry breaking, providing a direct link between microscopic order and experimentally observed spectral reconstruction. Combining this mechanism with the presence of lattice distortion effects, I will show how our simulations correctly account for three ubiquitous but previously unexplained experimental features: the persistence of finite-bias spectral peaks, the strong particle–hole asymmetry of the electronic compressibility, and the reduction of local-moment degeneracy at low temperatures. Finally, I will provide initial evidence on the nature of superconductivity in TBG, detailing how it emerges out of a broken flavor symmetry normal state. Altogether, these results establish a coherent microscopic understanding of how correlations, order, strain, and relaxation govern the behavior of TBG and related moiré materials.
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