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تسجيل مستخدم جديدRaman imaging of twist angle variations in twisted bilayer graphene at intermediate angles
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Van der Waals layered materials with well-defined twist angles between the crystal lattices of individual layers have attracted increasing attention due to the emergence of unexpected material properties. As many properties critically depend on the exact twist angle and its spatial homogeneity, there is a need for a fast and non-invasive characterization technique of the local twist angle, to be applied preferably right after stacking. We demonstrate that confocal Raman spectroscopy can be utilized to spatially map the twist angle in stacked bilayer graphene with an angle resolution of 0.01{deg} for angles between 6.5{deg} and 8{deg} when using a green excitation laser. The twist angles can directly be extracted from the moire superlattice-activated Raman scattering process of the transverse acoustic (TA) phonon mode. Furthermore, we show that the width of the TA Raman peak contains valuable information on spatial twist-angle variations on length scales below the laser spot size of ~ 500 nm.
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We study the zero-temperature many-body properties of twisted bilayer graphene with a twist angle equal to the so-called `first magic angle. The system low-energy single-electron spectrum consists of four (eight, if spin label is accounted) weakly-di
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Graphene bilayers exhibit zero-energy flat bands at a discrete series of magic twist angles. In the absence of intra-sublattice inter-layer hopping, zero-energy states satisfy a Dirac equation with a non-abelian SU(2) gauge potential that cannot be d
iagonalized globally. We develop a semiclassical WKB approximation scheme for this Dirac equation by introducing a dimensionless Plancks constant proportional to the twist angle, solving the linearized Dirac equation around AB and BA turning points, and connecting Airy function solutions via bulk WKB wavefunctions. We find zero energy solutions at a discrete set of values of the dimensionless Plancks constant, which we obtain analytically. Our analytic flat band twist angles correspond closely to those determined numerically in previous work.
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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 predicted t
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Van der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle
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