Spectroscopic Evidence for a Spin- and Valley-Polarized Metallic State in a Nonmagic-Angle Twisted Bilayer Graphene

Abstract

In the magic-angle twisted bilayer graphene (MA-TBG), strong electron-electron (e-e) correlations caused by the band-flattening lead to many exotic quantum phases such as superconductivity, correlated insulator, ferromagnetism, and quantum anomalous Hall effects, when its low-energy van Hove singularities (VHSs) are partially filled. Here our high-resolution scanning tunneling microscope and spectroscopy measurements demonstrate that the e-e correlation in a non-magic-angle TBG with a twist angle θ = 1.49º still plays an important role in determining its electronic properties. Our most interesting observation on that sample is that when one of its VHS is partially filled, the one associated peak in the spectrum splits into four peaks. Our analysis based on the continuum model suggests that such a one-to-four split of the VHS originates from the formation of an interaction-driven spin-valley-polarized metallic state near the VHS, lifting both the spin and valley degeneracies. Our results for this non-magic-angle TBG reveal a new symmetry-breaking phase, which has not been identified in the MA-TBG or in other systems.

Twistronics in graphene-based van der Waals structures

“…( 2), the two VHSs move closer to each other with decreasing the twist angles. Here we summarize the energy separations of the two VHSs ∆E VHS vs θ of the TBG acquired from the STS measurements [32,[34][35][36][37][38][39][40][67][68][69][70][71][72]97] as shown in Fig. 2.…”

“…These parameters are systematically measured by different groups in the past few years. [32][33][34][35][36][37][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81]126] In Figs. 3(b)-3(e), we summarize the ∆E VHS , the full-width at half-maximum (FWHM) of the VHSs, and the ∆ gap acquired 117303-3 from STS and transport measurements in the TBG near the magic angle, respectively.…”

Cascade of transitions in twisted and non-twisted graphene layers within the van Hove scenario

“…The vH scenario has been also discussed in context of chiral density wave and superconductivity in TBG (see e.g., refs. [23][24][25][26][27] ).…”

Moiré-Induced Transport in CVD-Based Small-Angle Twisted Bilayer Graphene

“…Recent developments in the synthesis process have allowed one to obtain a fraction of intermediate twist-angles (down to ∼3°), higher than in previous studies but lacking however deterministic control, as well as moiré transport signatures. To overcome this issue, one can employ a hybrid approach by stacking two CVD-grown SLG to form TBG, obtaining either large or SA twisting, as demonstrated by photoemission − and scanning probe experiments, , respectively. Although permitting high rotational accuracy in analogy to exfoliated flakes, sequentially stacked CVD-grown graphene layers tend to damage and accumulate contaminants at their interface .…”