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The Hamiltonian of the magic-angle twisted symmetric trilayer graphene (TSTG) can be decomposed into a TBG-like flat band Hamiltonian and a high-velocity Dirac fermion Hamiltonian. We use Hartree-Fock mean field approach to study the…

Mesoscale and Nanoscale Physics · Physics 2021-10-19 Fang Xie , Nicolas Regnault , Dumitru Călugăru , B. Andrei Bernevig , Biao Lian

We investigate twisted double bilayer graphene (TDBG), a four-layer system composed of two AB-stacked graphene bilayers rotated with respect to each other by a small angle. Our ab initio band structure calculations reveal a considerable…

Mesoscale and Nanoscale Physics · Physics 2020-04-22 Fatemeh Haddadi , QuanSheng Wu , Alex J. Kruchkov , Oleg V. Yazyev

We formulate the third harmonic generation (THG) within the dynamical mean field theory (DMFT) approximation of the Hubbard model. In the limit of large dimensions, where DMFT becomes exact, the vertex corrections to current vertices are…

Strongly Correlated Electrons · Physics 2009-11-11 S. A. Jafari , T. Tohyama , S. Maekawa

The recently-introduced Topological Heavy Fermion (THF) model [Phys. Rev. Lett. 129, 047601] of twisted bilayer graphene (TBG) aims to reconcile the quantum-dot-like electronic structure of the latter observed by scanning tunneling…

Strongly Correlated Electrons · Physics 2023-07-07 Dumitru Călugăru , Maksim Borovkov , Liam L. H. Lau , Piers Coleman , Zhi-Da Song , B. Andrei Bernevig

Twisted 2D layered materials have garnered a lot of attention recently as a class of 2D materials whose interlayer interactions and electronic properties are dictated by the relative rotation / twist angle between the adjacent layers. In…

Despite much theoretical work, developing a comprehensive ab initio model for twisted bilayer graphene (TBG) has proven challenging due to the inherent trade-off between accurately describing the band structure and incorporating the…

Strongly Correlated Electrons · Physics 2025-09-25 Run Hou , Shouvik Sur , Lucas K. Wagner , Andriy H. Nevidomskyy

Although the strongly interacting flat bands in twisted bilayer graphene (TBG) have been approached using the minimal Bistritzer-MacDonald (BM) Hamiltonian, there is mounting evidence that strain and lattice relaxation are essential in…

Mesoscale and Nanoscale Physics · Physics 2025-09-26 Jonah Herzog-Arbeitman , Jiabin Yu , Dumitru Călugăru , Haoyu Hu , Nicolas Regnault , Oskar Vafek , Jian Kang , B. Andrei Bernevig

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. We use Dynamical Mean Field Theory (DMFT) on the…

Lattice dynamics play a crucial role in the physics of Moir\'e systems. In twisted bilayer graphene (TBG), it was shown that, in addition to the graphene phonons, there is another set of gapless excitations termed Moir\'e Phonons [Phys.…

Mesoscale and Nanoscale Physics · Physics 2022-08-23 Qiang Gao , Eslam Khalaf

We present a theoretical study of the local optical conductivity, plasmon spectra, and thermoelectric properties of twisted bilayer graphene (TBG) at different filling factors and twist angles $\theta$. Our calculations are based on the…

Mesoscale and Nanoscale Physics · Physics 2020-09-04 Pietro Novelli , Iacopo Torre , Frank H. L. Koppens , Fabio Taddei , Marco Polini

Twisted bilayer graphene provides a paradigmatic platform for exploring the interplay between electronic topology and strong correlations. Within the topological heavy fermion model [Song and Bernevig, Phys. Rev. Lett. 129, 047601 (2022)],…

Strongly Correlated Electrons · Physics 2026-04-17 Nemin Wei , Felix von Oppen , Leonid I. Glazman

We derive the Hamiltonian for trilayer moir\'e systems with the Coulomb interaction projected onto the bands near the charge neutrality point. Motivated by the latest experimental results, we focus on the twisted symmetric trilayer graphene…

Strongly Correlated Electrons · Physics 2021-05-19 Dumitru Călugăru , Fang Xie , Zhi-Da Song , Biao Lian , Nicolas Regnault , B. Andrei Bernevig

We report the spectral features of a phase-shifted parity and time ($\mathcal{PT}$)-symmetric fiber Bragg grating (PPTFBG) and demonstrate its functionality as a demultiplexer in the unbroken $\mathcal{PT}$-symmetric regime. The length of…

Optics · Physics 2020-08-05 S. Vignesh Raja , A. Govindarajan , A. Mahalingam , M. Lakshmanan

We review the theoretical modelling of moir\'e materials, focusing on various aspects of magic-angle twisted bilayer graphene (MA-TBG) viewed through the lens of Hartree-Fock mean-field theory. We first provide an elementary introduction to…

Strongly Correlated Electrons · Physics 2026-03-20 Yves H. Kwan , Ziwei Wang , Glenn Wagner , Nick Bultinck , Steven H. Simon , Siddharth A. Parameswaran

We develop a theoretical framework for probing moir\'e phonon modes using Raman spectroscopy, and illustrate it with the example of twisted bilayer graphene (TBG). These moir\'e phonons arise from interlayer sliding motion in twisted 2D…

Strongly Correlated Electrons · Physics 2025-06-24 Vitor Dantas , Héctor Ochoa , Rafael M. Fernandes , Natalia B. Perkins

We present a theoretical study of the intrinsic plasmonic properties of twisted bilayer graphene (TBG) as a function of the twist angle $\theta$ (and other microscopic parameters such as temperature and filling factor). Our calculations,…

Mesoscale and Nanoscale Physics · Physics 2024-09-06 Lorenzo Cavicchi , Iacopo Torre , Pablo Jarillo-Herrero , Frank H. L. Koppens , Marco Polini

We study the interacting transport properties of twisted bilayer graphene (TBG) using the topological heavy-fermion (THF) model. In the THF model, TBG comprises localized, correlated $f$-electrons and itinerant, dispersive $c$-electrons. We…

Strongly Correlated Electrons · Physics 2024-02-23 Dumitru Călugăru , Haoyu Hu , Rafael Luque Merino , Nicolas Regnault , Dmitri K. Efetov , B. Andrei Bernevig

We consider a lattice model of twisted bilayer graphene (TBG) for incommensurate twist angles, focusing on the role of large-momentum-transfer Umklapp terms. These terms, which nearly connect the Fermi points of different layers, are…

Strongly Correlated Electrons · Physics 2026-03-31 Ian Jauslin , Vieri Mastropietro

Moir\'e superlattices created by the twisted stacking of two-dimensional crystalline monolayers can host electronic bands with flat energy dispersion in which interaction among electrons is strongly enhanced. These superlattices can also…

Mesoscale and Nanoscale Physics · Physics 2021-05-18 Xiaomeng Liu , Cheng-Li Chiu , Jong Yeon Lee , Gelareh Farahi , Kenji Watanabe , Takashi Taniguchi , Ashvin Vishwanath , Ali Yazdani

The dominance of Coulomb interactions over kinetic energy of electrons in narrow, non-trivial moir\'{e} bands of magic-angle twisted bilayer graphene (TBG) gives rise to a variety of correlated phases such as correlated insulators,…

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