Strain impacts on commensurate bilayer graphene superlattices: Distorted trigonal warping, emergence of bandgap and direct-indirect bandgap transition

Abstract

Due to low dimensionality, the controlled stacking of the graphene films and their electronic properties are susceptible to environmental changes including strain. The strain-induced modification of the electronic properties such as the emergence and modulation of bandgaps crucially depends on the stacking of the graphene films. However, to date, only the impact of strain on electronic properties of Bernal and AA-stacked bilayer graphene has been extensively investigated in theoretical studies. Exploiting density functional theory and tight-binding calculation, we investigate the impacts of in-plane strain on two different class of commensurate twisted bilayer graphene (TBG) which are even/odd under sublattice exchange (SE) parity. We find that the SE odd TBG remains gapless whereas the bandgap increases for the SE even TBG when applying equibiaxial tensile strain. Moreover, we observe that for extremely large mixed strains both investigated TBG superstructures demonstrate direct-indirect bandgap transition. arXiv:1809.08555v1 [cond-mat.mes-hall]

Imaging moiré deformation and dynamics in twisted bilayer graphene

“…1 f–i also show subtle distortions. As structural variations correlate directly with local electronic properties, we will quantify them in detail 5 , 6 . For this, we use adaptive geometric phase analysis (GPA), extending our earlier work on STM data of moiré patterns in TBG (see Supplementary Note 2 ) 31 – 35 .…”

Imaging moiré deformation and dynamics in twisted bilayer graphene

“…Despite their relative homogeneity, the moiré areas in Figure 1e-h also show subtle distortions. As structural variations correlate directly with local electronic properties, we quantify them in detail [5,6]. For this, we use adaptive geometric phase analysis (GPA), extending our earlier work on STM data of moiré patterns in TBG (see Supplementary Information) [29][30][31][32][33].…”

“…At the 'magic' twist angle θ m ≈ 1.1 • , this causes a flat band to form, yielding emergent properties such as correlated insulator behavior and superconductivity [1][2][3][4]. In general, the moiré structure in TBG varies spatially, influencing the local electronic properties [5][6][7][8][9] and hence the outcome of macroscopic charge transport experiments. In particular, to understand the wide variety observed in the phase diagrams and critical temperatures, a more detailed understanding of the local moiré variation is needed [10].…”

First-Principles Mapping of the Electronic Properties of Two-Dimensional Materials for Strain-Tunable Nanoelectronics

“…11,12 To bridge this gap, several authors have turned to mapping electronic structures of materials with respect to independent strain components. [13][14][15] Despite being naturally more informative, this approach has not gained due attention because its merits remain poorly outlined, and the number of considered 2d materials is still small.…”

“…11,12 To bridge this gap, several authors have turned to mapping electronic structures of materials with respect to independent strain components. [13][14][15] Despite being naturally more informative, this approach has not gained due attention because its merits remain poorly outlined, and the number of considered 2d materials is still small. Herein, we assess and adapt the methodology for mapping strain-induced changes in electronic structures of 2d materials for four representative compounds with different symmetries and bonding characters.…”