Soliton signature in the phonon spectrum of twisted bilayer graphene

Lamparski, Michael; Troeye, Benoît Van; Meunier, Vincent

doi:10.1088/2053-1583/ab7874

Cited by 41 publications

(51 citation statements)

References 39 publications

(77 reference statements)

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“…It is important to note here that the assumption of zone folding is only approximately correct. Very recently, it has been shown for twisted bilayer graphene [57] and MoS 2 [58] that interlayer coupling and lattice reconstruction can lead to frequency renormalizations and even sidebands [57] of phonons. Figure 1(c) shows a microscope image of one of the MoSe 2 homobilayers, which is prepared by the tear-and-stack technique.…”

Section: Resultsmentioning

confidence: 99%

Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons

et al. 2021

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We report about the investigation of twisted MoSe 2 homo-and MoSe 2 -WSe 2 heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence (µPL). In room-temperature LFRS experiments on both, twisted MoSe 2 homobilayers and twisted MoSe 2 -WSe 2 heterobilayers, we observe moiré phonons, i.e. folded acoustic phonon modes due to the moiré superlattice. In the heterobilayers, we can identify moiré phonons of both materials, MoSe 2 and WSe 2 . While the twist angles for the homobilayers are relatively precisely known from the applied tear-and-stack preparation method, the twist angles of the heterobilayers have to be determined via second-harmonic-generation microscopy on monolayer regions of the samples, which has significant uncertainties. We show that by the moiré phonons of the heterobilayers, the relative twist angles can be determined on a local scale with much higher precision. We apply our technique for the investigation of a large area H-type (twist angle θ = 60 • + δ) MoSe 2 -WSe 2 heterobilayer. These investigations show that spatial regions, which can be identified to be atomically reconstructed (i.e. δ = 0 • ) by the observation of an interlayer shear mode in LFRS experiments, exhibit a strong, momentum-allowed interlayer-exciton signal in low-temperature µPL. On the contrary, regions, where moiré phonons are observed, i.e. which can be identified to be rigidly twisted by a misalignment angle in the range of 5 • ≲ |δ| ≲ 6 • , exhibit no significant interlayer-exciton signals.

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Section: Resultsmentioning

confidence: 99%

Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons

et al. 2021

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“…Similar physics is being addressed also in twisted bilayers made out of transition-metal dichalcogenides [21], germanium selenide [19], and other two-dimensional materials [22][23][24]. That reveals how the twist angle can be used as a further degree of freedom [25] for combining two-dimensional (2D) materials to implement desired properties [26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 88%

“…A second, unexpected, insulating phase shows up at half-filling of the FB manifold, both on the electron and on the hole side (±2 electrons with respect to charge neutrality). The correlated insulating phase is attributed to enhanced electron-electron interaction within the FBs [14,15], although some authors are highlighting the relevance of the electron-phonon interaction [16][17][18][19]. After electrostatic doping, achieved by gating the structure, unconventional superconductivity with a critical temperature ranging from 1.7 to 3 K appears in a strong pairing regime, with a phase diagram very similar to that of the underdoped cuprates, whose origin is still to be understood [17,20].…”

Section: Introductionmentioning

confidence: 99%

Structural relaxation and low-energy properties of twisted bilayer graphene

Cantele

Conte

Cataudella

et al. 2020

Phys. Rev. Research

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The structural and electronic properties of twisted bilayer graphene are investigated from first-principles and tight-binding approach as a function of the twist angle (ranging from the first "magic" angle θ = 1.08 • to θ = 13.17 • , with the former corresponding to the largest unit cell, comprising 11,164 carbon atoms). By properly taking into account the long-range van der Waals (vdW) interaction, we provide the patterns for the atomic displacements (with respect to the ideal twisted bilayer). The out-of-plane relaxation shows an oscillating ("buckling") behavior, very evident for the smallest angles, with the atoms around the AA stacking regions interested by the largest displacements. The out-of-plane displacements are accompanied by a significant in-plane relaxation, showing a vortexlike pattern, where the vorticity (intended as curl of the displacement field) is reverted when moving from the top to the bottom plane and vice versa. Overall, the atomic relaxation results in the shrinking of the AA stacking regions in favor of the more energetically favorable AB/BA stacking domains. The measured flat bands emerging at the first magic angle can be accurately described only if the atomic relaxations are taken into account. Quite importantly, the experimental gaps separating the flat-band manifold from the higher and lower energy bands are intimately related to out-of-plane relaxations. The stability of the relaxed bilayer at the first magic angle is estimated to be of the order of 0.5-0.9 meV per atom (or 7-10 K). Our calculations shed light on the importance of an accurate description of the vdW interaction and of the resulting atomic relaxation to envisage the electronic structure of this really peculiar kind of vdW bilayers.

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“…In addition, tBLG with a small twist angle can be regarded as a network of graphene domain with AB/BA stacking order due to the reduction of unfavorable AA stacking regions caused by atomic relaxation in strain fields. [ 149 ] The transition region of AB/BA stacked bilayer graphene is an 1D soliton‐like domain wall, which is divided into the tensile (perpendicular to the Burgers vector) and shear (parallel to the Burgers vector) type ( Figure a,b). The formation of soliton networks in tBLG brings about the essential changes in plasmonic and electronic properties.…”

Section: Unique Properties Of Tblg and Corresponding Applicationsmentioning

confidence: 99%

Fabrication Strategies of Twisted Bilayer Graphenes and Their Unique Properties

Cai

2021

Advanced Materials

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Therefore, graphene becomes a rising star on the horizon of materials science. Since the first report of centimeter-scale single-crystal graphene by Ruoff group showed high electrical quality, [9] great achievements have been made in the fabrication of high-quality graphene for the application in electronic devices, including single-crystalline graphene flakes, [10,11] super-ordered graphene structures, [12,13] super-clean graphene films, [14-16] and ultra-flat graphene films. [17] However, the zero-bandgap feature for monolayer graphene has limited its potential applications in semiconductors. In addition, the negligible mass, low yield, and high production costs of graphene are insurmountable bottlenecks for the practical application in energy conversion and storage. In particular, the absence of killer applications leads to the increased difficulty in graphene commercialization. [18,19] Nevertheless, it is undeniable that the unique structure of graphene has sparked intense interest in condensed matter physics, such as fractional quantum Hall effects, [17] proton permeation, [20] and plasmons. [21] More interestingly, twisted bilayer graphene (tBLG), which is similar to the van der Waals heterostructures, has a dramatic effect on the electronic properties. [22,23] The relative rotating graphene layers become a powerful model to study topological physical properties, including ferromagnetism, [24] Mott insulating behavior and superconducting behaviors, [25,26] topological valley transport, [27] van Hove singularities, [28] and tunable bandgap. [29] Consequently, the twisted structure of tBLG has triggered tremendous enthusiasm, even inspiring the formation of a new field for twisted 2D materials. Currently, production methods of tBLG contain chemical vapor deposition (CVD) on metal catalysts; [30] epitaxial growth on SiC substrate; [31] folding monolayer graphene, [32] and stacking monolayer graphene. [33] These methods are divided into two categories: direct growth and manual assembly. Generally, the direct growth of tBLG undergoes an in situ rearrangement of carbon atoms in the non-equilibrium state at high temperatures, whereas the ex situ vertical overlap of monolayer graphene by transfer process is the basic principle for manual assembly. The completely different preparation processes give rise to the distinctive advantages and disadvantages, but precise control over twist angle and super-clean interface are the ultimate pursuits for any preparation method. Recent progress in Twisted bilayer graphene (tBLG) exhibits a host of innovative physical phenomena owing to the formation of moiré superlattice. Especially, the discovery of superconducting behavior has generated new interest in graphene. The growing studies of tBLG mainly focus on its physical properties, while the fabrication of high-quality tBLG is a prerequisite for achieving the desired properties due to the great dependence on the twist angle and the interfacial contact. Here, the cutting-edge preparation strategies and challenges of tBLG fabrica...

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Soliton signature in the phonon spectrum of twisted bilayer graphene

Cited by 41 publications

References 39 publications

Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons

Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons

Structural relaxation and low-energy properties of twisted bilayer graphene

Fabrication Strategies of Twisted Bilayer Graphenes and Their Unique Properties

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Soliton signature in the phonon spectrum of twisted bilayer graphene

Cited by 41 publications

References 39 publications

Moiré phonons in twisted MoSe2–WSe2 heterobilayers and their correlation with interlayer excitons

Moiré phonons in twisted MoSe2–WSe2 heterobilayers and their correlation with interlayer excitons

Structural relaxation and low-energy properties of twisted bilayer graphene

Fabrication Strategies of Twisted Bilayer Graphenes and Their Unique Properties

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Product

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Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons

Moiré phonons in twisted MoSe₂–WSe₂ heterobilayers and their correlation with interlayer excitons