Raman spectra of twisted bilayer graphene close to the magic angle

Abstract In this work, we study the Raman spectra of twisted bilayer graphene samples as a function of their twist-angles (θ), ranging from 0.03º to 3.40º, where local θ are determined by analysis of their associated moiré superlattices, as imaged by scanning microwave impedance microscopy. Three standard excitation laser lines are used (457, 532, and 633 nm wavelengths), and the main Raman active graphene bands (G and 2D) are considered. Our results reveal that electron-phonon interaction influences the G band's linewidth close to the magic angle regardless of laser excitation wavelength. Also, the 2D band lineshape in the θ < 1º regime is dictated by crystal lattice and depends on both the Bernal (AB and BA) stacking bilayer graphene and strain soliton regions (SP) [1]. We propose a geometrical model to explain the 2D lineshape variations, and from it, we estimate the SP width when moving towards the magic angle.

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Effective continuum model for relaxed twisted bilayer graphene and moiré electron-phonon interaction

Physical Review B ◽

10.1103/physrevb.101.195425 ◽

2020 ◽

Vol 101 (19) ◽

Cited By ~ 1

Author(s):

Mikito Koshino ◽

Nguyen N. T. Nam

Keyword(s):

Continuum Model ◽

Bilayer Graphene ◽

Phonon Interaction ◽

Electron Phonon Interaction ◽

Twisted Bilayer Graphene

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Quantifying the Charge Carrier Interaction in Metallic Twisted Bilayer Graphene Superlattices

Nanomaterials ◽

10.3390/nano11051306 ◽

2021 ◽

Vol 11 (5) ◽

pp. 1306

Author(s):

Evgueni F. Talantsev

Keyword(s):

Charge Carrier ◽

Bilayer Graphene ◽

Electron Interaction ◽

Temperature Dependent ◽

Phonon Interaction ◽

Linear Temperature ◽

Electron Phonon Interaction ◽

Wide Range ◽

Carrier Interaction ◽

Twisted Bilayer Graphene

The mechanism of charge carrier interaction in twisted bilayer graphene (TBG) remains an unresolved problem, where some researchers proposed the dominance of the electron–phonon interaction, while the others showed evidence for electron–electron or electron–magnon interactions. Here we propose to resolve this problem by generalizing the Bloch–Grüneisen equation and using it for the analysis of the temperature dependent resistivity in TBG. It is a well-established theoretical result that the Bloch–Grüneisen equation power-law exponent, p, exhibits exact integer values for certain mechanisms. For instance, p = 5 implies the electron–phonon interaction, p = 3 is associated with the electron–magnon interaction and p = 2 applies to the electron–electron interaction. Here we interpret the linear temperature-dependent resistance, widely observed in TBG, as p→1, which implies the quasielastic charge interaction with acoustic phonons. Thus, we fitted TBG resistance curves to the Bloch–Grüneisen equation, where we propose that p is a free-fitting parameter. We found that TBGs have a smoothly varied p-value (ranging from 1.4 to 4.4) depending on the Moiré superlattice constant, λ, or the charge carrier concentration, n. This implies that different mechanisms of the charge carrier interaction in TBG superlattices smoothly transition from one mechanism to another depending on, at least, λ and n. The proposed generalized Bloch–Grüneisen equation is applicable to a wide range of disciplines, including superconductivity and geology.

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