Electron–phonon and electron–electron interaction effects in twisted bilayer graphene

Abstract

By comparing with recently available experimental data from several groups, we critically discuss the manifestation of continuum many body interaction effects in twisted bilayer graphene (tBLG) with small twist angles and low carrier densities, which arise naturally within the Dirac cone approximation for the non-interacting band structure. We provide two specific examples of such continuum many body theories: one involving electron-phonon interaction and one involving electron-electron interaction. In both cases, the experimental findings are only partially quantitatively consistent with rather clear-cut leading-order theoretical predictions based on well-established continuum many body theories. We provide a critical discussion, based mainly on the currently available tBLG experimental data, on possible future directions for understanding many body renormalization involving electron-phonon and electron-electron interactions in the system. arXiv:1910.08556v1 [cond-mat.mes-hall]

Strange metallicity of moiré twisted bilayer graphene

“…1 arises (at least partially) from acoustic phonon scattering, using a minimal Dirac model for the tBLG band structure. This viewpoint has earlier been propounded in our theoretical works [9,10] in the context of the tBLG experimental works in [2,3]. Ref.…”

“…weak/strong dependence on ν/θ) is easily explainable based on the phonon scattering mechanism, as discussed below and in our earlier work. [9,10] One should remember that each twist angle in Fig. 2 corresponds to a different sample, with likely unknown variations arising from disorder [14] and twist angle fluctuations [15], making a direct quantitative comparison between results at different angles difficult (and perhaps also explaining some of the nonmonotonicity and the crossing of various lines for |ν| > 1).…”

Observation of logarithmic Kohn anomaly in monolayer graphene

“…The observation of LKA in monolayer graphene would provide a firm basis for various unique phenomena. In addition, considering that the nonadiabatic EPIs may play a vital role in the superconducting pairing of twisted bilayer graphene [13,14,[48][49][50][51][52][53][54][55], our work might spark significant attention and may offer insight into the underlying physics of superconductivity in magic-angle graphene superlattices.…”

Giant thermopower and power factor in magic angle twisted bilayer graphene at low temperature

“…The recent remarkable and exciting experimental discoveries in twisted bilayer graphene (tBLG), particularly the existence of correlated insulating phases and superconductivity at low temperatures, and a highly resistive linear-in-temperature resistivity ρ at high temperature, have created tremendous interest in the study of electronic properties of this material [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. A small twist angle θ between the two layers modifies the electronic structure in to moire flat band with θ dependent suppressed Fermi velocity ν F * (θ), which is very much smaller than the bare Fermi velocity ν F in monolayer graphene, consequently leading to a large density of states D(E k ) in the neighborhood of magic angle θ m at which ν F * (θ) = 0 [10,13,14,16]. The θ near θm, acts as one of the tunable parameters in limiting the electronic properties of tBLG, apart from the carrier density n s and temperature T [1,2,4,[9][10][11]13].…”