scholarly journals Photonic crystals for nano-light in moiré graphene superlattices

Science ◽  
2018 ◽  
Vol 362 (6419) ◽  
pp. 1153-1156 ◽  
Author(s):  
S. S. Sunku ◽  
G. X. Ni ◽  
B. Y. Jiang ◽  
H. Yoo ◽  
A. Sternbach ◽  
...  
Keyword(s):  
Graphene Layer ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Tuning Parameter ◽  
Low Loss ◽  
Quantum Properties ◽  
Twisted Bilayer Graphene ◽  
Van Der Waals Materials ◽  
Nano Imaging ◽  
Plasmon Polaritons

Graphene is an atomically thin plasmonic medium that supports highly confined plasmon polaritons, or nano-light, with very low loss. Electronic properties of graphene can be drastically altered when it is laid upon another graphene layer, resulting in a moiré superlattice. The relative twist angle between the two layers is a key tuning parameter of the interlayer coupling in thus-obtained twisted bilayer graphene (TBG). We studied the propagation of plasmon polaritons in TBG by infrared nano-imaging. We discovered that the atomic reconstruction occurring at small twist angles transforms the TBG into a natural plasmon photonic crystal for propagating nano-light. This discovery points to a pathway for controlling nano-light by exploiting quantum properties of graphene and other atomically layered van der Waals materials, eliminating the need for arduous top-down nanofabrication.

scholarly journals Quasicrystalline 30° twisted bilayer graphene as an incommensurate superlattice with strong interlayer coupling

2018 ◽  
Vol 115 (27) ◽  
pp. 6928-6933 ◽  
Author(s):  
Wei Yao ◽  
Eryin Wang ◽  
Changhua Bao ◽  
Yiou Zhang ◽  
Kenan Zhang ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Graphene Layer ◽  
Rotational Symmetry ◽  
Reciprocal Lattice ◽  
Double Resonance ◽  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Lattice Vector ◽  
Graphene Layers ◽  
Twisted Bilayer Graphene

The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moiré period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence. Here we report the successful growth of quasicrystalline 30° twisted bilayer graphene (30°-tBLG), which is stabilized by the Pt(111) substrate, and reveal its electronic structure. The 30°-tBLG is confirmed by low energy electron diffraction and the intervalley double-resonance Raman mode at 1383 cm−1. Moreover, the emergence of mirrored Dirac cones inside the Brillouin zone of each graphene layer and a gap opening at the zone boundary suggest that these two graphene layers are coupled via a generalized Umklapp scattering mechanism—that is, scattering of a Dirac cone in one graphene layer by the reciprocal lattice vector of the other graphene layer. Our work highlights the important role of interlayer coupling in incommensurate quasicrystalline superlattices, thereby extending band structure engineering to incommensurate superstructures.

scholarly journals Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene

Nano Research ◽  
2021 ◽  
Author(s):  
Eva A. A. Pogna ◽  
Xianchong Miao ◽  
Driele von Dreifus ◽  
Thonimar V. Alencar ◽  
Marcus V. O. Moutinho ◽  
...  
Keyword(s):  
Electronic Band Structure ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Relaxation Dynamics ◽  
Carrier Distribution ◽  
Absorption Bands ◽  
Electronic Band ◽  
Angle Dependence ◽  
Twisted Bilayer Graphene

AbstractVan der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle has opened new possibilities for tailoring the optoelectronic properties of these heterostructures. Twisted bilayer graphene with a strong interlayer coupling is a prototype of twisted heterostructure inheriting the intriguing electronic properties of graphene. Understanding the effects of the twist angle on its out-of-equilibrium optical properties is crucial for devising optoelectronic applications. With this aim, we here combine excitation-resolved hot photoluminescence with femtosecond transient absorption microscopy. The hot charge carrier distribution induced by photo-excitation results in peaked absorption bleaching and photo-induced absorption bands, both with pronounced twist angle dependence. Theoretical simulations of the electronic band structure and of the joint density of states enable to assign these bands to the blocking of interband transitions at the van Hove singularities and to photo-activated intersubband transitions. The tens of picoseconds relaxation dynamics of the observed bands is attributed to the angle-dependence of electron and phonon heat capacities of twisted bilayer graphene.

scholarly journals Realization of nearly dispersionless bands with strong orbital anisotropy from destructive interference in twisted bilayer MoS2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lede Xian ◽  
Martin Claassen ◽  
Dominik Kiese ◽  
Michael M. Scherer ◽  
Simon Trebst ◽  
...  
Keyword(s):  
Collective Behavior ◽  
Twist Angle ◽  
Honeycomb Lattice ◽  
Destructive Interference ◽  
Two Dimensional ◽  
Marked Contrast ◽  
Flat Bands ◽  
Emergent Phenomena ◽  
Twisted Bilayer Graphene ◽  
Van Der Waals Materials

AbstractRecently, the twist angle between adjacent sheets of stacked van der Waals materials emerged as a new knob to engineer correlated states of matter in two-dimensional heterostructures in a controlled manner, giving rise to emergent phenomena such as superconductivity or correlated insulating states. Here, we use an ab initio based approach to characterize the electronic properties of twisted bilayer MoS2. We report that, in marked contrast to twisted bilayer graphene, slightly hole-doped MoS2 realizes a strongly asymmetric px-py Hubbard model on the honeycomb lattice, with two almost entirely dispersionless bands emerging due to destructive interference. The origin of these dispersionless bands, is similar to that of the flat bands in the prototypical Lieb or Kagome lattices and co-exists with the general band flattening at small twist angle due to the moiré interference. We study the collective behavior of twisted bilayer MoS2 in the presence of interactions, and characterize an array of different magnetic and orbitally-ordered correlated phases, which may be susceptible to quantum fluctuations giving rise to exotic, purely quantum, states of matter.

scholarly journals Realization of nearly dispersionless bands with strong orbital anisotropy from destructive interference in twisted bilayer MoS2

2020 ◽  
Author(s):  
Lede Xian ◽  
Martin Claassen ◽  
Dominik Kiese ◽  
Michael M. Scherer ◽  
Simon Trebst ◽  
...  
Keyword(s):  
Collective Behavior ◽  
Twist Angle ◽  
Quantum States ◽  
Honeycomb Lattice ◽  
Destructive Interference ◽  
Marked Contrast ◽  
Flat Bands ◽  
Emergent Phenomena ◽  
Twisted Bilayer Graphene ◽  
Van Der Waals Materials

Abstract Recently, the twist angle between adjacent sheets of stacked van der Waals materials emerged as a new knob to engineer correlated states of matter in twodimensional heterostructures in a controlled manner, giving rise to emergent phenomena such as superconductivity or correlated insulating states. Here, we use an ab initio based approach to characterize the electronic properties of twisted bilayer MoS2. We report that, in marked contrast to twisted bilayer graphene, slightly hole-doped MoS2 realizes a strongly asymmetric px-py Hubbard model on the honeycomb lattice, with two almost entirely dispersionless bands emerging due to destructive interference. The origin of these dispersionless bands, is similar to that of the flat bands in the prototypical Lieb or Kagome lattices and co-exists with the general band flattening at small twist angle due to the Moir´e interference. We study the collective behavior of twisted bilayer MoS2 in the presence of interactions, and characterize an array of different magnetic and orbitally-ordered correlated phases, which may be susceptible to quantum fluctuations giving rise to exotic, purely quantum, states of matter.

scholarly journals Tuning superconductivity in twisted bilayer graphene

Science ◽  
2019 ◽  
Vol 363 (6431) ◽  
pp. 1059-1064 ◽  
Author(s):  
Matthew Yankowitz ◽  
Shaowen Chen ◽  
Hryhoriy Polshyn ◽  
Yuxuan Zhang ◽  
K. Watanabe ◽  
...  
Keyword(s):  
Twist Angle ◽  
Interlayer Coupling ◽  
Interlayer Spacing ◽  
Bilayer Graphene ◽  
Superconducting Phase ◽  
Low Energy ◽  
Flat Band ◽  
Strong Correlations ◽  
Twisted Bilayer Graphene ◽  
Quantum Phenomena

Materials with flat electronic bands often exhibit exotic quantum phenomena owing to strong correlations. An isolated low-energy flat band can be induced in bilayer graphene by simply rotating the layers by 1.1°, resulting in the appearance of gate-tunable superconducting and correlated insulating phases. In this study, we demonstrate that in addition to the twist angle, the interlayer coupling can be varied to precisely tune these phases. We induce superconductivity at a twist angle larger than 1.1°—in which correlated phases are otherwise absent—by varying the interlayer spacing with hydrostatic pressure. Our low-disorder devices reveal details about the superconducting phase diagram and its relationship to the nearby insulator. Our results demonstrate twisted bilayer graphene to be a distinctively tunable platform for exploring correlated states.

scholarly journals Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

2012 ◽  
Vol 109 (18) ◽  
Author(s):  
Taisuke Ohta ◽  
Jeremy T. Robinson ◽  
Peter J. Feibelman ◽  
Aaron Bostwick ◽  
Eli Rotenberg ◽  
...  
Keyword(s):  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Periodic Potentials ◽  
Twisted Bilayer Graphene

Grating-coupler based low-loss optical interlayer coupling

2011 ◽  
Author(s):  
Jin Yao ◽  
Xuezhe Zheng ◽  
Guoliang Li ◽  
Ivan Shubin ◽  
Hiren Thacker ◽  
...  
Keyword(s):  
Interlayer Coupling ◽  
Grating Coupler ◽  
Low Loss

scholarly journals Electronic Properties of Twisted Bilayer Graphene in the Presence of a Magnetic Field

2020 ◽  
Vol 233 ◽  
pp. 03004
Author(s):  
M.F.C. Martins Quintela ◽  
J.C.C. Guerra ◽  
S.M. João
Keyword(s):  
Magnetic Field ◽  
Electronic Properties ◽  
Twist Angle ◽  
Bilayer Graphene ◽  
Polynomial Method ◽  
Zero Energy ◽  
Energy Bands ◽  
Optical And Electronic Properties ◽  
Twisted Bilayer Graphene ◽  
Kernel Polynomial Method

In AA-stacked twisted bilayer graphene, the lower energy bands become completely flat when the twist angle passes through certain specific values: the so-called “magic angles”. The Dirac peak appears at zero energy due to the flattening of these bands when the twist angle is sufficiently small [1-3]. When a constant perpendicular magnetic field is applied, Landau levels start appearing as expected [5]. We used the Kernel Polynomial Method (KPM) [6] as implemented in KITE [7] to study the optical and electronic properties of these systems. The aim of this work is to analyze how the features of these quantities change with the twist angle in the presence of an uniform magnetic field.

scholarly journals Layered THz waveguides for SPPs, filter and sensor applications

2019 ◽  
Vol 48 (4) ◽  
pp. 567-581 ◽  
Author(s):  
Jiamin Liu ◽  
Zia Ullah Khan ◽  
Siamak Sarjoghian
Keyword(s):  
Refractive Index ◽  
Layered Structure ◽  
Dielectric Slab ◽  
Low Loss ◽  
Sensor Applications ◽  
Te Mode ◽  
Tm Mode ◽  
Mode Characteristics ◽  
Plasmon Polaritons ◽  
Thz Waveguides

Abstract Theory of five kinds of layered structure THz waveguides is presented. In these waveguides, the modified and hybrid THz surface plasmon-polaritons (SPPs) are researched in detail. On these modes, the effects of material in each layer are discussed. The anti-resonant reflecting mechanism is also discussed in these waveguides. The mode characteristics of both TM mode and TE mode are analyzed for guiding TM mode with low loss and TE modes with huge loss in one waveguide: the TE modes filter application is put forward. The mode characteristics for one waveguide have useful sensor applications: for TE1 mode, we find that the low cut-off frequency has a sensitivity (S) to the refractive index of the dielectric slab. The highest S can be 666.7 GHz/RIU when n2 = 1.5, w = 0 and t = 0.1 mm. We believe these results are very useful for designing practical THz devices for SPPs, filter and sensor applications.

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