The plethora of electronic phases in twisted bilayer graphene (TBG) gives strong evidence of the importance of electronic correlations in this system. While the effect of correlations often leads to phase transitions to ordered states, evidences in other strongly correlated electron systems have shown that the non-ordered normal state or the so-called parent state can be also strongly modified by such correlations. Among various correlated states of TBG, the anomalous cascade phenomena detected in scanning tunneling microscopy and single electron transistor measurements stand out [1-3]. The cascades involve larger energy scales and happen in a wider range of temperatures and twist angles than other correlated states, suggesting that the former constitutes the parent state of the latter.
We investigate the effect of correlations in the normal state of TBG by applying a self-consistent dynamical mean field theory + Hartree approximation to a multi-orbital model of TBG . Such a theoretical analysis of the system has been so far hampered by the complexity of the minimal models for TBG and by the implementation of strong coupling techniques required in such models. We show that the spectral weight reorganization associated with the formation of local moments and heavy quasiparticles due to the correlation effect is responsible for the cascade phenomena. Our findings of the doping and energy dependence of the spectral weight and of the compressibility show remarkable similarities with experimental results.
1. D. Wong et al., Nature 582, 198 (2020).
2. U. Zondiner et al., Nature 582, 203 (2020).
3. Y. Choi et al., Nature 589, 536 (2021).
4. A. Datta, M. J. Calderón, A. Camjayi, E. Bascones, arXiv:2301.13024.