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1. Dirac Fermion Cloning, Moiré Flat Bands, and Magic Lattice Constants in Epitaxial Monolayer Graphene

   https://doi.org/10.1002/adma.202200625  

   Lu, Qiangsheng; Le, Congcong; Zhang, Xiaoqian; Cook, Jacob; He, Xiaoqing; Zarenia, Mohammad; Vaninger, Mitchel; Miceli, Paul_F; Singh, David_J; Liu, Chang; et al (May 2022, Advanced Materials)

   Abstract Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed‐matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. In this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the supercell of graphene. The results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many‐body quantum phases arising from interactions between Dirac electrons. 

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2. Gate-tunable Veselago interference in a bipolar graphene microcavity

   https://doi.org/10.1038/s41467-022-34347-w  

   Zhang, Xi; Ren, Wei; Bell, Elliot; Zhu, Ziyan; Tsai, Kan-Ting; Luo, Yujie; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Luskin, Mitchell; et al (December 2022, Nature Communications)

   Abstract The relativistic charge carriers in monolayer graphene can be manipulated in manners akin to conventional optics. Klein tunneling and Veselago lensing have been previously demonstrated in ballistic graphene pn-junction devices, but collimation and focusing efficiency remains relatively low, preventing realization of advanced quantum devices and controlled quantum interference. Here, we present a graphene microcavity defined by carefully-engineered local strain and electrostatic fields. Electrons are manipulated to form an interference path inside the cavity at zero magnetic field via consecutive Veselago refractions. The observation of unique Veselago interference peaks via transport measurement and their magnetic field dependence agrees with the theoretical expectation. We further utilize Veselago interference to demonstrate localization of uncollimated electrons and thus improvement in collimation efficiency. Our work sheds new light on relativistic single-particle physics and provide a new device concept toward next-generation quantum devices based on manipulation of ballistic electron trajectory. 

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3. Engineering anisotropic electrodynamics at the graphene/CrSBr interface

   https://doi.org/10.1038/s41467-025-56804-y  

   Rizzo, Daniel J; Seewald, Eric; Zhao, Fangzhou; Cox, Jordan; Xie, Kaichen; Vitalone, Rocco A; Ruta, Francesco L; Chica, Daniel G; Shao, Yinming; Shabani, Sara; et al (December 2025, Nature Communications)

   Abstract Graphene is a privileged 2D platform for hosting confined light-matter excitations known as surface plasmon polaritons (SPPs), as it possesses low intrinsic losses and a high degree of optical confinement. However, the isotropic nature of graphene limits its ability to guide and focus SPPs, making it less suitable than anisotropic elliptical and hyperbolic materials for polaritonic lensing and canalization. Here, we present graphene/CrSBr as an engineered 2D interface that hosts highly anisotropic SPP propagation across mid-infrared and terahertz energies. Using scanning tunneling microscopy, scattering-type scanning near-field optical microscopy, and first-principles calculations, we demonstrate mutual doping in excess of 10¹³cm^–2holes/electrons between the interfacial layers of graphene/CrSBr. SPPs in graphene activated by charge transfer interact with charge-induced electronic anisotropy in the interfacial doped CrSBr, leading to preferential SPP propagation along the quasi-1D chains that compose each CrSBr layer. This multifaceted proximity effect both creates SPPs and endows them with anisotropic propagation lengths that differ by an order-of-magnitude between the in-plane crystallographic axes of CrSBr. 

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4. Magnetic-Field-Driven Electron Dynamics in Graphene

   https://doi.org/10.1021/acs.jpclett.1c01020  

   Fatima, F.; Inerbaev, T; Xia, W; Kilin, D. (May 2021, The journal of physical chemistry letters)

   null (Ed.)

   Graphene exhibits unique optoelectronic properties originating from the band structure at the Dirac points. It is an ideal model structure to study the electronic and optical properties under the influence of the applied magnetic field. In graphene, electric field, laser pulse, and voltage can create electron dynamics which is influenced by momentum dispersion. However, computational modeling of momentum-influenced electron dynamics under the applied magnetic field remains challenging. Here, we perform computational modeling of the photoexcited electron dynamics achieved in graphene under an applied magnetic field. Our results show that magnetic field leads to local deviation from momentum conservation for charge carriers. With the increasing magnetic field, the delocalization of electron probability distribution increases and forms a cyclotron-like trajectory. Our work facilitates understanding of momentum resolved magnetic field effect on non-equilibrium properties of graphene, which is critical for optoelectronic and photovoltaic applications. 

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5. Broken symmetries and excitation spectra of interacting electrons in partially filled Landau levels

   https://doi.org/10.1038/s41567-023-02126-z  

   Farahi, Gelareh; Chiu, Cheng-Li; Liu, Xiaomeng; Papic, Zlatko; Watanabe, Kenji; Taniguchi, Takashi; Zaletel, Michael P.; Yazdani, Ali (January 2023, Nature Physics)

   Interacting electrons in flat bands give rise to a variety of quantum phases. One fundamental aspect of such states is the ordering of the various flavours—such as spin or valley—that the electrons can possess and the excitation spectrum of the broken-symmetry states that they form. These properties cannot be probed directly with electrical transport measurements. The zeroth Landau level of monolayer graphene with fourfold spin–valley degeneracy is a model system for such investigations, but the nature of its broken-symmetry states—particularly at partial fillings—is still not understood. Here we demonstrate a non-invasive spectroscopic technique with a scanning tunnelling microscope and use it to perform measurements of the valley polarization of the electronic wavefunctions and their excitation spectrum in the partially filled zeroth Landau level of graphene. We can extract information such as the strength of the Haldane pseudopotentials that characterize the repulsive interactions underlying the fractional quantum states. Our experiments also demonstrate that fractional quantum Hall phases are built upon broken-symmetry states that persist at partial filling. Our experimental approach quantifies the valley phase diagram of the partially filled Landau level as a model flat-band platform, which is applicable to other graphene-based electronic systems. 

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