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 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 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 Flat bands in slightly twisted bilayer graphene: Tight-binding calculations

2010 ◽  
Vol 82 (12) ◽  
Author(s):  
E. Suárez Morell ◽  
J. D. Correa ◽  
P. Vargas ◽  
M. Pacheco ◽  
Z. Barticevic
Keyword(s):  
Tight Binding ◽  
Bilayer Graphene ◽  
Flat Bands ◽  
Twisted Bilayer Graphene

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 Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Doried Ghader
Keyword(s):  
Band Structure ◽  
Magnetic Order ◽  
Condensed Matter ◽  
Twist Angle ◽  
Band Gaps ◽  
Novel Device ◽  
Flat Bands ◽  
Research Fields ◽  
Active Research ◽  
The Continuum

Abstract Twistronics is currently one of the most active research fields in condensed matter physics, following the discovery of correlated insulating and superconducting phases in twisted bilayer graphene (tBLG). Here, we present a magnonic analogue of tBLG. We study magnons in twisted ferromagnetic bilayers (tFBL) with collinear magnetic order, including exchange and weak Dzyaloshinskii-Moriya interactions (DMI). For negligible DMI, tFBL presents discrete magnon magic angles and flat moiré minibands analogous to tBLG. The DMI, however, changes the picture and renders the system much more exotic. The DMI in tFBL induces a rich topological magnon band structure for any twist angle. The twist angle turns to a control knob for the magnon valley Hall and Nernst conductivities. Gapped flat bands appear in a continuum of magic angles in tFBL with DMI. In the lower limit of the continuum, the band structure reconstructs to form several topological flat bands. The luxury of twist-angle control over band gaps, topological properties, number of flat bands, and valley Hall and Nernst conductivities renders tFBL a novel device from fundamental and applied perspectives.

scholarly journals Theory of correlated insulating behaviour and spin-triplet superconductivity in twisted double bilayer graphene

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Jong Yeon Lee ◽  
Eslam Khalaf ◽  
Shang Liu ◽  
Xiaomeng Liu ◽  
Zeyu Hao ◽  
...  
Keyword(s):  
Displacement Field ◽  
Twist Angle ◽  
Vertical Displacement ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Hartree Fock ◽  
Flat Bands ◽  
Half Filling ◽  
Spin Triplet ◽  
Experimental Findings

AbstractTwo graphene monolayers twisted by a small magic angle exhibit nearly flat bands, leading to correlated electronic states. Here we study a related but different system with reduced symmetry - twisted double bilayer graphene (TDBG), consisting of two Bernal stacked bilayer graphenes, twisted with respect to one another. Unlike the monolayer case, we show that isolated flat bands only appear on application of a vertical displacement field. We construct a phase diagram as a function of twist angle and displacement field, incorporating interactions via a Hartree-Fock approximation. At half-filling, ferromagnetic insulators are stabilized with valley Chern number $${C}_{{\rm{v}}}=\pm 2$$Cv=±2. Upon doping, ferromagnetic fluctuations are argued to lead to spin-triplet superconductivity from pairing between opposite valleys. We highlight a novel orbital effect arising from in-plane fields plays an important role in interpreting experiments. Combined with recent experimental findings, our results establish TDBG as a tunable platform to realize rare phases in conventional solids.

scholarly journals Moiré with flat bands is different

2019 ◽  
Vol 50 (3) ◽  
pp. 24-26
Author(s):  
Tero T. Heikkilä ◽  
Timo Hyart
Keyword(s):  
Critical Temperature ◽  
Fermi Surface ◽  
Room Temperature ◽  
Electronic States ◽  
Bilayer Graphene ◽  
Flat Bands ◽  
Twisted Bilayer Graphene

Recent experimental discoveries of superconductivity and other exotic electronic states in twisted bilayer graphene (TBG) call for a reconsideration of our traditional theories of these states, usually based on the assumption of the presence of a Fermi surface. Here we show how such developments may even help us finding mechanisms of increasing the critical temperature of superconductivity towards the room temperature.

scholarly journals Dirac electrons in a dodecagonal graphene quasicrystal

Science ◽  
2018 ◽  
Vol 361 (6404) ◽  
pp. 782-786 ◽  
Author(s):  
Sung Joon Ahn ◽  
Pilkyung Moon ◽  
Tae-Hoon Kim ◽  
Hyun-Woo Kim ◽  
Ha-Chul Shin ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Rotation Angle ◽  
Rotational Symmetry ◽  
Interlayer Coupling ◽  
Quantum States ◽  
Translational Symmetry ◽  
Two Dimensional ◽  
Ambient Conditions ◽  
Entire Sample ◽  
Twisted Bilayer Graphene

Quantum states of quasiparticles in solids are dictated by symmetry. We have experimentally demonstrated quantum states of Dirac electrons in a two-dimensional quasicrystal without translational symmetry. A dodecagonal quasicrystalline order was realized by epitaxial growth of twisted bilayer graphene rotated exactly 30°. We grew the graphene quasicrystal up to a millimeter scale on a silicon carbide surface while maintaining the single rotation angle over an entire sample and successfully isolated the quasicrystal from a substrate, demonstrating its structural and chemical stability under ambient conditions. Multiple Dirac cones replicated with the 12-fold rotational symmetry were observed in angle-resolved photoemission spectra, which revealed anomalous strong interlayer coupling with quasi-periodicity. Our study provides a way to explore physical properties of relativistic fermions with controllable quasicrystalline orders.

scholarly journals Spin excitations in metallic kagome lattice FeSn and CoSn

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yaofeng Xie ◽  
Lebing Chen ◽  
Tong Chen ◽  
Qi Wang ◽  
Qiangwei Yin ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Inelastic Neutron Scattering ◽  
Spin Waves ◽  
Inelastic Neutron ◽  
Spin Excitation ◽  
Destructive Interference ◽  
Kagome Lattice ◽  
Kagomé Lattice ◽  
Flat Bands ◽  
Spin Excitations

AbstractIn two-dimensional (2D) metallic kagome lattice materials, destructive interference of electronic hopping pathways around the kagome bracket can produce nearly localized electrons, and thus electronic bands that are flat in momentum space. When ferromagnetic order breaks the degeneracy of the electronic bands and splits them into the spin-up majority and spin-down minority electronic bands, quasiparticle excitations between the spin-up and spin-down flat bands should form a narrow localized spin-excitation Stoner continuum coexisting with well-defined spin waves in the long wavelengths. Here we report inelastic neutron scattering studies of spin excitations in 2D metallic kagome lattice antiferromagnetic FeSn and paramagnetic CoSn, where angle resolved photoemission spectroscopy experiments found spin-polarized and nonpolarized flat bands, respectively, below the Fermi level. Our measurements on FeSn and CoSn reveal well-defined spin waves extending above 140 meV and correlated paramagnetic scattering around Γ point below 90 meV, respectively. In addition, we observed non-dispersive excitations at ~170 meV and ~360 meV arising mostly from hydrocarbon scattering of the CYTOP-M used to glue the samples to aluminum holder. Therefore, our results established the evolution of spin excitations in FeSn and CoSn, and identified anomalous flat modes overlooked by the neutron scattering community for many years.

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