scholarly journals Magic in twisted transition metal dichalcogenide bilayers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Trithep Devakul ◽  
Valentin Crépel ◽  
Yang Zhang ◽  
Liang Fu
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Anomalous Hall Effect ◽  
Quantum Spin ◽  
Flat Band ◽  
Magic Angle ◽  
Transition Metal Dichalcogenide ◽  
Strongly Correlated Electron ◽  
Hartree Fock ◽  
The Rich

AbstractThe long-wavelength moiré superlattices in twisted 2D structures have emerged as a highly tunable platform for strongly correlated electron physics. We study the moiré bands in twisted transition metal dichalcogenide homobilayers, focusing on WSe2, at small twist angles using a combination of first principles density functional theory, continuum modeling, and Hartree-Fock approximation. We reveal the rich physics at small twist angles θ < 4∘, and identify a particular magic angle at which the top valence moiré band achieves almost perfect flatness. In the vicinity of this magic angle, we predict the realization of a generalized Kane-Mele model with a topological flat band, interaction-driven Haldane insulator, and Mott insulators at the filling of one hole per moiré unit cell. The combination of flat dispersion and uniformity of Berry curvature near the magic angle holds promise for realizing fractional quantum anomalous Hall effect at fractional filling. We also identify twist angles favorable for quantum spin Hall insulators and interaction-induced quantum anomalous Hall insulators at other integer fillings.

scholarly journals Flat-band topology of magic angle graphene on a transition metal dichalcogenide

2020 ◽  
Vol 102 (23) ◽  
Author(s):  
Tianle Wang ◽  
Nick Bultinck ◽  
Michael P. Zaletel
Keyword(s):  
Transition Metal ◽  
Flat Band ◽  
Magic Angle ◽  
Transition Metal Dichalcogenide

scholarly journals Spin-textured Chern bands in AB-stacked transition metal dichalcogenide bilayers

2021 ◽  
Vol 118 (36) ◽  
pp. e2112673118
Author(s):  
Yang Zhang ◽  
Trithep Devakul ◽  
Liang Fu
Keyword(s):  
Transition Metal ◽  
Displacement Field ◽  
Anomalous Hall Effect ◽  
Quantum Spin ◽  
Transition Metal Dichalcogenide ◽  
First Principle ◽  
First Principle Calculations ◽  
Hall Effects ◽  
Topological States ◽  
Spin Texture

While transition-metal dichalcogenide (TMD)–based moiré materials have been shown to host various correlated electronic phenomena, topological states have not been experimentally observed until now [T. Li et al., Quantum anomalous Hall effect from intertwined moiré bands. arXiv [Preprint] (2021). https://arxiv.org/abs/2107.01796 (Accessed 5 July 2021)]. In this work, using first-principle calculations and continuum modeling, we reveal the displacement field–induced topological moiré bands in AB-stacked TMD heterobilayer MoTe2/WSe2. Valley-contrasting Chern bands with nontrivial spin texture are formed from interlayer hybridization between MoTe2 and WSe2 bands of nominally opposite spins. Our study establishes a recipe for creating topological bands in AB-stacked TMD bilayers in general, which provides a highly tunable platform for realizing quantum-spin Hall and interaction-induced quantum anomalous Hall effects.

scholarly journals Conditions for electronic hybridization between transition-metal dichalcogenide monolayers and physisorbed carbon-conjugated molecules

2021 ◽  
Author(s):  
Jannis Krumland ◽  
Caterina Cocchi
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Mutual Arrangement ◽  
Transition Metal Dichalcogenide ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Electronic Interactions ◽  
Organic Interfaces ◽  
The Individual ◽  
Hybrid Density Functional

Abstract Hybridization effects play a crucial role in determining the electronic properties of hybrid inorganic/organic interfaces. To gain insight into these important interactions, we perform a first-principles study based on hybrid density-functional theory including spin-orbit coupling, focusing on eight representative systems formed by two carbon-conjugated molecules-pyrene and perylene-physisorbed on the transition-metal dichalcogenide monolayers (TMDCs) MoS2, MoSe2 WS2, and WSe2. By means of band unfolding techniques, we analyze the band structures of the considered materials, identifying the contributions of the individual constituents as well as the signatures of their hybridization. Based on symmetry and energetic arguments, we derive general conditions for electronic hybridization between conjugated molecules and underlying TMDCs even when the former do not lie planar on the latter, thus providing the key to predict how their mutual arrangement affect their electronic interactions.

scholarly journals The transition metal to ligand bonding nature: A quantum chemical study of π-allyl-ruthenacycle molecule

2018 ◽  
Vol 58 (3) ◽  
Author(s):  
Aušra Vektarienė
Keyword(s):  
Transition Metal ◽  
Physical Properties ◽  
Density Functional ◽  
Quantum Chemical Study ◽  
Decomposition Analysis ◽  
Computational Procedure ◽  
Chemical Study ◽  
Hartree Fock ◽  
Charge Decomposition Analysis ◽  
The Density Functional Theory

Understanding of the transition metal (TM) to ligand (L) bonding nature is important for characterization of experimental observations. One of the methods to explain the TM to L interactions is the Dewar–Chatt–Duncanson (DCD) model. However, in most applications the validity of the DCD model is based on assumptions in order to explain trends in vibrational spectroscopy or other physical properties of TM complexes. In this paper the computational methodology for treatment of the π-allyl-ruthenacycle complex based on the density functional theory, restricted Hartree–Fock method, natural bond orbital and charge decomposition analysis is reported. It is shown how the DCD model emerges from the presented calculation scheme and how it relates with the physical properties and stability of this complex. It is important to note that in this work the determination of the DCD model operation is based on the defined computational procedure, not postulated beforehand. The calculated geometry parameters, vibrational frequencies and electron density arrangement for the π-allyl-ruthenacycle complex are in good agreement with the experiment and support the DCD model.

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

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Minhao He ◽  
Ya-Hui Zhang ◽  
Yuhao Li ◽  
Zaiyao Fei ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Anomalous Hall Effect ◽  
Bilayer Graphene ◽  
Flat Band ◽  
Zero Field ◽  
First Order ◽  
Orbital Magnetism ◽  
Valley Polarization ◽  
The Rich ◽  
Topological Phase Transitions

AbstractFlat 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.

scholarly journals Tunable topology and berry curvature dipole in transition metal dichalcogenide Janus monolayers

2021 ◽  
Author(s):  
Nesta Joseph ◽  
Saswata Roy ◽  
Awadhesh Narayan
Keyword(s):  
Transition Metal ◽  
Hall Effect ◽  
Transition Metal Dichalcogenides ◽  
Tight Binding ◽  
Quantum Spin ◽  
Transition Metal Dichalcogenide ◽  
Berry Curvature ◽  
Asymmetric Structures ◽  
Non Linear ◽  
Metal Dichalcogenides

Abstract Janus transition metal dichalcogenides, with intrinsic mirror asymmetry, exhibit a wide array of interesting properties. In this work, we study Janus monolayers derived from WTe2 using first-principles and tight-binding calculations. We discover that WSeTe and WSTe are topologically trivial, in contrast to the parent quantum spin Hall insulator WTe2. Motivated by the growing interest in non-linear Hall effect, which also requires asymmetric structures, we investigate the Berry curvature and its dipole in these Janus systems and find that they exhibit strikingly large values of Berry curvature dipole, despite being in the topologically trivial phase. We track down the origin of this behaviour and put forth a low-energy massive Dirac model to understand the central features of our ab inito computations. Our predictions introduce Janus monolayers as promising new platforms for exploring as well as engineering non-linear Hall effect.

scholarly journals Revised M06 density functional for main-group and transition-metal chemistry

2018 ◽  
Vol 115 (41) ◽  
pp. 10257-10262 ◽  
Author(s):  
Ying Wang ◽  
Pragya Verma ◽  
Xinsheng Jin ◽  
Donald G. Truhlar ◽  
Xiao He
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Noncovalent Interactions ◽  
Molecular Data ◽  
Main Group ◽  
Molecular Structures ◽  
Transition Metal Chemistry ◽  
Excitation Energies ◽  
Metal Chemistry ◽  
Hartree Fock

We present a hybrid metageneralized-gradient-approximation functional, revM06, which is based on adding Hartree–Fock exchange to the revM06-L functional form. Compared with the original M06 suite of density functionals, the resulting revM06 functional has significantly improved across-the-board accuracy for both main-group and transition-metal chemistry. The revM06 functional improves on the M06-2X functional for main-group and transition-metal bond energies, atomic excitation energies, isomerization energies of large molecules, molecular structures, and both weakly and strongly correlated atomic and molecular data, and it shows a clear improvement over M06 and M06-2X for noncovalent interactions, including smoother potential curves for rare-gas dimers. The revM06 functional also predicts more accurate results than M06 and M06-2X for most of the outside-the-training-set test sets examined in this study. Therefore, the revM06 functional is well-suited for a broad range of chemical applications for both main-group and transition-metal elements.

Graphene and The Advent of Other Layered-2D Materials for Nanoelectronics, Photonics and Related Applications

2013 ◽  
Vol 1549 ◽  
pp. 11-16
Author(s):  
Anupama B. Kaul
Keyword(s):  
Transition Metal ◽  
Flexible Electronics ◽  
Layered Material ◽  
Transition Metal Dichalcogenide ◽  
Material System ◽  
Recent Emergence ◽  
Direct Band ◽  
The Rich ◽  
Near Future ◽  
Rich Spectrum

ABSTRACTCarbon-based nanostructures have been the center of intense research and development for more than two decades now. Of these materials, graphene, a two-dimensional (2D) layered material system, has had a significant impact on science and technology in recent years after it was experimentally isolated in single layers in 2004. The recent emergence of other classes of 2D layered systems beyond graphene has added yet more exciting and new dimensions for research and exploration given their diverse and rich spectrum of properties. For example, h-BN a layered material closest in structure to graphene, is an insulator, while NbSe, a transition metal dichalcogenide is metallic and monolayers of other transition metal di-chalcogenides such as MoS2 are direct band-gap semiconductors. The rich variety of properties that 2D layered material systems offer can potentially be engineered on-demand, and creates exciting prospects for their device and technological applications ranging from electronics, sensing, photonics, energy harvesting and flexible electronics in the near future.

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