Topological flat bands in twisted trilayer graphene

Ma, Zhen; Li, Shuai; Zheng, Ya-Wen; Xiao, Mengmeng; Jiang, Hua; Gao, Jin-Hua; Xie, X. C.

doi:10.1016/j.scib.2020.10.004

Cited by 63 publications

(43 citation statements)

References 32 publications

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“…4 ∘14-16 . The absence of robust correlated insulating states is likely a consequence of the larger bandwidth compared with the D > 0 bands [17][18][19] . Supplementary Note 4 and Supplementary Table 1 provide a detailed summary of the correlated states observed in our three devices, as well as those previously reported in refs.…”

Section: Resultsmentioning

confidence: 99%

“…The bandwidth, W, and valley Chern number, C v , additionally depend on the orientation of D (Supplementary Fig. 1) [17][18][19] , which can polarize charge carriers more strongly towards either the monolayer or Bernal-stacked bilayer graphene sheet 14 . The high tunability of the bands with the combination of twist angle, doping, D, and magnetic field makes tMBG an attractive platform for investigating the nature of closely competing correlated and topological ground states.…”

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confidence: 99%

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Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

Zhang

et al. 2021

Nat Commun

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Flat band moiré superlattices have recently emerged as unique platforms for investigating the interplay between strong electronic correlations, nontrivial band topology, and multiple isospin ‘flavor’ symmetries. Twisted monolayer-bilayer graphene (tMBG) is an especially rich system owing to its low crystal symmetry and the tunability of its bandwidth and topology with an external electric field. Here, we find that orbital magnetism is abundant within the correlated phase diagram of tMBG, giving rise to the anomalous Hall effect in correlated metallic states nearby most odd integer fillings of the flat conduction band, as well as correlated Chern insulator states stabilized in an external magnetic field. The behavior of the states at zero field appears to be inconsistent with simple spin and valley polarization for the specific range of twist angles we investigate, and instead may plausibly result from an intervalley coherent (IVC) state with an order parameter that breaks time reversal symmetry. The application of a magnetic field further tunes the competition between correlated states, in some cases driving first-order topological phase transitions. Our results underscore the rich interplay between closely competing correlated ground states in tMBG, with possible implications for probing exotic IVC ordering.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

Zhang

et al. 2021

Nat Commun

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“…a band gap tunable with an out-of-plane displacement field 19 . The symmetry is further reduced in tTLG, by stacking mono-and bi-layer graphene together with a small relative twist angle 20,21 , resulting into ABA-, ABB-and ABC-stacked domains. In this report, we observed electron-hole asymmetry, tunable van Hove singularities as well as correlated insulating states at commensurate fillings on the electron side under finite displacement field in tTLG.…”

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confidence: 99%

“…s1) which demonstrates that the structure of the states we observe is not an artefact. Therefore, the asymmetry with respect to D could be related to the lack of symmetry in tTLG 21 . To be consistent, we define positive D when electric fields point from monolayer to bilayer graphene (see Fig.…”

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confidence: 99%

Tunable van Hove singularities and correlated states in twisted monolayer–bilayer graphene

et al. 2021

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Understanding and tuning correlated states is of great interest and significance to modern condensed matter physics. The recent discovery of unconventional superconductivity and Mott-like insulating states in magic-angle twisted bilayer graphene (tBLG) presents a unique platform to study correlation phenomena, in which the Coulomb energy dominates over the quenched kinetic energy as a result of hybridized flat bands. Extending this approach to the case of twisted multilayer graphene would allow even higher control over the band structure because of the reduced symmetry of the system. Here, we study electronic transport properties in twisted trilayer graphene (tTLG, bilayer on top of monolayer graphene heterostructure). We observed the formation of van Hove singularities which are highly tunable by twist angle and displacement field and can cause strong correlation effects under optimum conditions, including superconducting states. We provide basic theoretical interpretation of the observed electronic structure.Van der Waals heterostructures technology provides a variety of tuning knobs, including twist angle, displacement field, and stacking order, for band engineering by precise stacking of one atomically thin crystal onto another 1 . The lattice constant mismatch and relative twist angle give rise to a moiré superlattice, where, under some conditions, interlayer hybridization leads to the formation of an isolated low energy flat band, which quenches the kinetic energy of electronic system. Such low-energy subbands have been realised in several structures and emergent phenomena have been reported, including Mott-like insulators 2 , unconventional superconductivity [3][4][5] and ferromagnetism 6,7 in twisted bilayer graphene (tBLG) and twisted double bilayer graphene (tDBLG) [8][9][10][11] . Similar correlated states have also been reported in ABC-trilayer graphene (TLG) superlattice on hexagonal boron nitride (hBN) and rhombohedral stacked graphite films [12][13][14] .In this work, we study small-angle twisted trilayer graphene (tTLG) van der Waals heterostructures, where a monolayer graphene (MLG) and bilayer graphene (BLG) are stacked and rotated by a small angle with respect to each other. Compared to tBLG, more tuning knobs are expected in tTLG, since the band structures in multi-layer graphene are more tunable than that of the monolayer counterpart [15][16][17][18] . In particular, there naturally exists two stacking orders in trilayer graphene, Bernal (ABA)-stacking with mirror symmetry and rhombohedral (ABC)-stacking with inversion symmetry. The former is semimetallic, while the latter is known to be semiconducting with

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“…[34] The flat band voltage (E fb ) of these photo-catalyst samples can be calculated by extrapolating the tangent line of Mott-Schottky curve to the intersection point of X-axis. [58] In the Figure 5, the E fb values of TiO 2 , g-C 3 N 4 and NiO are À 0.19 eV, À 1.46 eV and 0.08 eV (vs. SCE), respectively. The semiconductor's conduction band potential (E CB ) is equal to the E fb of the n-type semiconductor and the semiconductor's valence band potential (E VB ) is equal to the E fb of the p-type semiconductor.…”

Section: Resultsmentioning

confidence: 92%

A Ternary Photocatalyst with Double Heterojunctionsfor Efficient Diesel Oil Degradation

et al. 2021

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The photodegradation is a potential technology to solve environmental issues such as the diesel oil pollution. The titanium dioxide/graphitic carbon nitride (TiO 2 /g-C 3 N 4 ) photocatalyst is widely used for the photodegradation of pollutants. However, the performances of this binary photocatalyst such as the degradation efficiency and cyclic stability are still unsatisfactory for real applications. In our work, we introduce a ptype NiO semiconductor into the binary TiO 2 /g-C 3 N 4 (98: 2) photocatalyst by a simple dipping method. The NiO semiconductor can form double heterojunctions with the TiO 2 and g-C 3 N 4 (dual Z-scheme and Z-scheme + p-n), which can accelerate the separation of photo-generated electron-hole pairs effectively. Thus, the as-obtained ternary TiO 2 /NiO/g-C 3 N 4 (TCN) sample delivers a good photocatalytic performance for diesel oil degradation under a simulated sunlight. Specifically, the TCN (7 : 3) photocatalyst exhibits a 98.94 % degradation efficiency after 2 h of visible-light, largely outperforming the single-component photocatalysts (TiO 2 , g-C 3 N 4 , NiO,) and the binary TiO 2 /g-C 3 N 4 (98 : 2) photocatalyst. The free radical capture test manifests that �O À 2 is the major factor on the degradation. This work presents a typical example to boost the photodegradation performance via a ternary catalyst design, which will provide valuable insight for the future high-performance diesel oil degradation.

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Topological flat bands in twisted trilayer graphene

Cited by 63 publications

References 32 publications

Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

Tunable van Hove singularities and correlated states in twisted monolayer–bilayer graphene

A Ternary Photocatalyst with Double Heterojunctionsfor Efficient Diesel Oil Degradation

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