Tunable correlated states and spin-polarized phases in twisted bilayer–bilayer graphene

Cao, Yuan; Rodan-Legrain, Daniel; Rubies-Bigordà, Oriol; Park, Jeong Min; Watanabe, Kenji; Taniguchi, Takashi; Jarillo‐Herrero, Pablo

doi:10.1038/s41586-020-2260-6

Cited by 557 publications

(444 citation statements)

References 32 publications

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“…One interesting possibility is the twisted doublebilayer. This four-layer system [28][29][30] has a relative twist between two untwisted bilayers, and it is expected to have flat bands whose properties depend on an even wider range of tunable variables compared with simple TBG. Another option is to place a graphene multilayer system on a hexagonal boron nitride substrate, which modifies the multilayer's properties [31,32].…”

Section: Beyond the Simple Bilayermentioning

confidence: 99%

Bilayer Graphene’s Wicked, Twisted Road

MacDonald

2019

Physics

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Section: Beyond the Simple Bilayermentioning

confidence: 99%

Bilayer Graphene’s Wicked, Twisted Road

MacDonald

2019

Physics

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“…Besides TBG, twisted double bilayer graphene (TDBG) with relative rotation between the top and bottom graphene bilayers has been realized recently [28][29][30] . In addition to the nearly flat middle bands in TDBG with a small θ, a gap at E F is opened, and among various stacking arrangements between the bilayers AB-BA TDBG can become valley Hall insulators [31][32][33][34][35] .…”

Section: Introductionmentioning

confidence: 99%

Pressure-induced gap modulation and topological transitions in twisted bilayer and twisted double bilayer graphene

Lin

Zhu

2020

Phys. Rev. B

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We study the electronic and topological properties of fully relaxed twisted bilayer (TBG) and double bilayer (TDBG) graphene under perpendicular pressure. An approach has been proposed to obtain the equilibrium in-plane structural deformation and out-of-plane corrugation in moiré superlattices under pressure. We find that the in-plane relaxation becomes much stronger under higher pressure, while the corrugation height in each layer is maintained. The comparison between band structures of relaxed and rigid structures demonstrates that not only the gaps on the electron and hole sides (∆e and ∆ h) are significantly underestimated without relaxation but also the detailed dispersions of the middle bands of rigid structures are rather different from those of relaxed systems. ∆e and ∆ h in TBG reach maximum values around critical pressures with narrowest middle bands. Topological transitions occur in TDBG under pressure with the middle valence and conduction bands in one valley touching and their Chern numbers transferred to each other. The pressure can also tune the gap at the neutrality point of TDBG, which becomes closed for a pressure range and reopened under higher pressure. The behavior of electronic structure of supertlattices under pressure is sensitive to the twist angle θ with the critical pressures generally increase with θ.

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“…The perpendicular electric field has a profound effect on the band structure of TDBG [7][8][9][10][11] . As depicted in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…T he advancement in twistronics has opened up new avenues to study electron correlations physics, such as Mott insulator states [1][2][3] , superconductivity 3,4 , and orbital ferromagnetism 5,6 in twisted bilayer graphene (TBG). Recent experiments in twisted double bilayer graphene (TDBG) [7][8][9][10][11] and trilayer graphene aligned to hexagonal boron nitride (hBN) [12][13][14] also reveal correlation effects. While low-energy flat bands enhance electronic correlations [15][16][17] , such moiré systems support topological bands with nonzero valley Chern number 5,6,14,18,19 .…”

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confidence: 99%

Bulk valley transport and Berry curvature spreading at the edge of flat bands

et al. 2020

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2D materials based superlattices have emerged as a promising platform to modulate band structure and its symmetries. In particular, moiré periodicity in twisted graphene systems produces flat Chern bands. The recent observation of anomalous Hall effect (AHE) and orbital magnetism in twisted bilayer graphene has been associated with spontaneous symmetry breaking of such Chern bands. However, the valley Hall state as a precursor of AHE state, when time-reversal symmetry is still protected, has not been observed. Our work probes this precursor state using the valley Hall effect. We show that broken inversion symmetry in twisted double bilayer graphene (TDBG) facilitates the generation of bulk valley current by reporting experimental evidence of nonlocal transport in a nearly flat band system. Despite the spread of Berry curvature hotspots and reduced quasiparticle velocities of the carriers in these flat bands, we observe large nonlocal voltage several micrometers away from the charge current path — this persists when the Fermi energy lies inside a gap with large Berry curvature. The high sensitivity of the nonlocal voltage to gate tunable carrier density and gap modulating perpendicular electric field makes TDBG an attractive platform for valley-twistronics based on flat bands.

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Tunable correlated states and spin-polarized phases in twisted bilayer–bilayer graphene

Cited by 557 publications

References 32 publications

Bilayer Graphene’s Wicked, Twisted Road

Bilayer Graphene’s Wicked, Twisted Road

Pressure-induced gap modulation and topological transitions in twisted bilayer and twisted double bilayer graphene

Bulk valley transport and Berry curvature spreading at the edge of flat bands

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