Magic angle
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Origin of Magic Angles in Twisted Bilayer Graphene Open
Twisted bilayer graphene (TBG) was recently shown to host superconductivity when tuned to special "magic angles" at which isolated and relatively flat bands appear. However, until now the origin of the magic angles and their irregular patt…
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Strange Metal in Magic-Angle Graphene with near Planckian Dissipation Open
Recent experiments on magic-angle twisted bilayer graphene have discovered correlated insulating behavior and superconductivity at a fractional filling of an isolated narrow band. Here we show that magic-angle bilayer graphene exhibits ano…
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Cascade of phase transitions and Dirac revivals in magic-angle graphene Open
Twisted bilayer graphene near the magic angle1,2,3,4 exhibits rich electron-correlation physics, displaying insulating3,4,5,6, magnetic7,8 and superconducting phases4,5,6. The electronic bands of this system were predicted1,2,3,,2 to narro…
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Faithful tight-binding models and fragile topology of magic-angle bilayer graphene Open
Correlated insulators and superconductivity have been observed in “magic-angle” twisted bilayer graphene, when the nearly flat bands close to neutrality are partially filled. Here, while a momentum-space continuum model accurately describe…
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Failure of Nielsen-Ninomiya Theorem and Fragile Topology in Two-Dimensional Systems with Space-Time Inversion Symmetry: Application to Twisted Bilayer Graphene at Magic Angle Open
We show that the Wannier obstruction and the fragile topology of the nearly flat bands in twisted bilayer graphene at magic angle are manifestations of the nontrivial topology of two-dimensional real wave functions characterized by the Eul…
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Band structure of twisted bilayer graphene: Emergent symmetries, commensurate approximants, and Wannier obstructions Open
A remarkable feature of the band structure of bilayer graphene at small twist angle is the appearance of isolated bands near neutrality, whose bandwidth can be reduced at certain magic angles (e.g., θ∼1.05°). In this regime, correlated ins…
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Magic angle hierarchy in twisted graphene multilayers Open
When two monolayers of graphene are stacked with a small relative twist angle, the resulting band structure exhibits a remarkably flat pair of bands at a sequence of "magic angles" where correlation effects can induce a host of exotic phas…
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Magic Angle Spectroscopy Open
The electronic properties of heterostructures of atomically-thin van der Waals (vdW) crystals can be modified substantially by Moiré superlattice potentials arising from an interlayer twist between crystals. Moiré-tuning of the band struct…
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Phonon-induced giant linear-in- resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity Open
We study the effect of electron-acoustic phonon interactions in twisted bilayer graphene on resistivity in the high-temperature transport and superconductivity in the low-temperature phase diagram. We theoretically show that twisted bilaye…
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Pressure dependence of the magic twist angle in graphene superlattices Open
The recently demonstrated unconventional superconductivity in twisted bilayer\ngraphene (tBLG) opens the possibility for interesting applications of\ntwo-dimensional layers that involve correlated electron states. Here we explore\nthe poss…
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Flat bands in twisted double bilayer graphene Open
Flatbands with extremely narrow bandwidths on the order of a few mili-electron volts can appear in twisted multilayer graphene systems for appropriate system parameters. Here we investigate the electronic structure of a twisted bi-bilayer …
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Mean-field theory for superconductivity in twisted bilayer graphene Open
Recent experiments show how a bilayer graphene twisted around a certain magic\nangle becomes superconducting as it is doped into a region with approximate\nflat bands. We investigate the mean-field $s$-wave superconducting state in\nsuch a…
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Multiflat Bands and Strong Correlations in Twisted Bilayer Boron Nitride: Doping-Induced Correlated Insulator and Superconductor Open
Two-dimensional materials, obtained by van der Waals stacking of layers, are fascinating objects of contemporary condensed matter research, exhibiting a variety of new physics. Inspired by the breakthroughs of twisted bilayer graphene (TBG…
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Geometric and Conventional Contribution to the Superfluid Weight in Twisted Bilayer Graphene Open
By tuning the angle between graphene layers to specific "magic angles" the lowest energy bands of twisted bilayer graphene (TBLG) can be made flat. The flat nature of the bands favors the formation of collective ground states and, in parti…
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Possible correlated insulating states in magic-angle twisted bilayer graphene under strongly competing interactions Open
We investigate correlated insulating states in magic-angle twisted bilayer\ngraphene (TBG) by the exact diagonalization method applied to the extended\nHubbard model with interaction parameters recently evaluated in the realistic\neffectiv…
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Electronic Compressibility of Magic-Angle Graphene Superlattices Open
We report the first electronic compressibility measurements of magic-angle twisted bilayer graphene. The evolution of the compressibility with carrier density offers insights into the interaction-driven ground state that have not been acce…
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Unconventional sequence of correlated Chern insulators in magic-angle twisted bilayer graphene Open
The interplay between strong electron-electron interactions and band topology can lead to novel electronic states that spontaneously break symmetries. The discovery of flat bands in magic-angle twisted bilayer graphene (MATBG) with nontriv…
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Flat Bands in Magic-Angle Bilayer Photonic Crystals at Small Twists Open
The new physics of magic-angle twisted bilayer graphene (TBG) motivated extensive studies of flat bands hosted by moiré superlattices in van der Waals structures, inspiring the investigations into their photonic counterparts with potential…
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Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy: Advances in Methodology and Applications Open
Solid-state NMR spectroscopy is one of the most commonly used techniques to study the atomic-resolution structure and dynamics of various chemical, biological, material, and pharmaceutical systems spanning multiple forms, including crystal…
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Proton-Based Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy Open
Protons are vastly abundant in a wide range of exciting macromolecules and thus can be a powerful probe to investigate the structure and dynamics at atomic resolution using solid-state NMR (ssNMR) spectroscopy. Unfortunately, the high sign…
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Spin-orbit driven ferromagnetism at half moir\'e filling in magic-angle twisted bilayer graphene Open
Strong electron correlation and spin-orbit coupling (SOC) provide two non-trivial threads to condensed matter physics. When these two strands of physics come together, a plethora of quantum phenomena with novel topological order have been …
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Combination of solid state NMR and DFT calculation to elucidate the state of sodium in hard carbon electrodes Open
We examined the state of sodium electrochemically inserted in HC prepared at 700–2000 °C using solid state Na magic angle spinning (MAS) NMR and multiple quantum (MQ) MAS NMR.
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Multiple topological transitions in twisted bilayer graphene near the first magic angle Open
Recent experiments have observed strongly correlated physics in twisted\nbilayer graphene (TBG) at very small angles, along with nearly flat electron\nbands at certain fillings. A good starting point in understanding the physics\nis a cont…
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Strain-Induced Quantum Phase Transitions in Magic-Angle Graphene Open
We investigate the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene. Using both self-consistent Hartree-Fock and density-matrix renormalization group calculations, we find that small …
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Protein NMR Spectroscopy at 150 kHz Magic‐Angle Spinning Continues To Improve Resolution and Mass Sensitivity Open
Spectral resolution is the key to unleashing the structural and dynamic information contained in NMR spectra. Fast magic‐angle spinning (MAS) has recently revolutionized the spectroscopy of biomolecular solids. Herein, we report a further …
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Dynamic Nuclear Polarization Enhancement of 200 at 21.15 T Enabled by 65 kHz Magic Angle Spinning Open
Solid-state nuclear magnetic resonance under magic angle spinning (MAS) enhanced with dynamic nuclear polarization (DNP) is a powerful approach to characterize many important classes of materials, allowing access to previously inaccessible…
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Electronic phases in twisted bilayer graphene at magic angles as a result of Van Hove singularities and interactions Open
This paper was published in the journal Physical Review B and is also available at https://doi.org/10.1103/PhysRevB.98.205151.
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Formation of Bloch Flat Bands in Polar Twisted Bilayers without Magic Angles Open
The existence of Bloch flat bands of electrons provides a facile pathway to obtain exotic quantum phases owing to strong correlation. Despite the established magic angle mechanism for twisted bilayer graphene, understanding of the emergenc…
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Twisted graphene bilayer around the first magic angle engineered by heterostrain Open
Very recently, twisted graphene bilayer (TGB) around the first magic angle\n1.1{\\deg} has attracted much attention for the realization of exotic quantum\nstates, such as correlated insulator behavior and unconventional\nsuperconductivity.…
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Dynamic nuclear polarization at 40 kHz magic angle spinning Open
DNP-enhanced solid-state NMR spectroscopy is shown to maintain performance over a wide range of sample spinning rates up to 40 kHz.