Angle-Dependent van Hove Singularities in a Slightly Twisted Graphene Bilayer

Abstract

Recent studies show that two low-energy van Hove singularities (VHSs) seen as two pronounced peaks in the density of states could be induced in a twisted graphene bilayer. Here, we report angle-dependent VHSs of a slightly twisted graphene bilayer studied by scanning tunneling microscopy and spectroscopy. We show that energy difference of the two VHSs follows ΔE(vhs)∼ℏν(F)ΔK between 1.0° and 3.0° [here ν(F)∼1.1 × 10(6) m/s is the Fermi velocity of monolayer graphene, and ΔK = 2Ksin(θ/2) is the shift between the corresponding Dirac points of the twisted graphene bilayer]. This result indicates that the rotation angle between graphene sheets does not result in a significant reduction of the Fermi velocity, which quite differs from that predicted by band structure calculations. However, around a twisted angle θ∼1.3°, the observed ΔE(vhs)∼0.11 eV is much smaller than the expected value ℏν(F)ΔK∼0.28 eV at 1.3°. The origin of the reduction of ΔE(vhs) at 1.3° is discussed.

Tunable moiré bands and strong correlations in small-twist-angle bilayer graphene

“…Because we expect a strong dependence of electronic properties on twist angle, it is critically important that the angle achieved by the rotation process be directly measured. To this end, we use scanning tunneling microscopy and spectroscopy to examine the topography of the longwavelength moiré patterns and their local electronic properties (11,(24)(25)(26)(27). The SPM samples are realized using the techniques of Fig.…”

Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer

“…The energies of these LLs follow the progression of LLs of massless Dirac Fermions, which suggest a possible route to realize zero-field quantum Hall effects in the strained graphene [11][12][13][14][15] . Compared with single-layer graphene, graphene bilayers, including AA stacked, AB stacked (Bernal) and twisted graphene bilayer, display even more complex electronic band structures and intriguing properties because of the interplay of quasiparticles between the Dirac cones on each layer [16][17][18][19][20][21][22][23][24][25][26][27][28] . Recently, several groups addressed the physics of the strained graphene bilayer (either AA-or AB-stacked graphene bilayer) theoretically and obtained many interesting results [29][30][31][32][33][34] .…”

Electronic properties of twisted bilayer nanoribbons

“…For these low rotation angles, states near the Fermi level are mostly localized in the AA region, with a strong localization, giving rise to the bright areas of the moiré pattern [4,5]. The flattening of the bands with diminishing angle has been experimentally observed in angle-dependent Van Hove singularities revealed in density of states measurements by scanning tunneling spectroscopy [10,14,20] and by an increase of the intensity of Raman modes measured in TBG samples [21,22].…”