Topological Phase and Quantum Anomalous Hall Effect in Ferromagnetic Transition-Metal Dichalcogenides Monolayer 1T-VSe2.
TL;DR: In this paper, the electronic structures and topological properties of the 2D ferromagnetic transition-metal dichalcogenides (TMD) monolayer 1T-VSe2 by first-principles calculations with the Heyd-Scuseria-Ernzerhof (HSE) functional were investigated.
Abstract: Magnetic two-dimensional (2D) van der Waals materials have attracted tremendous attention because of their high potential in spintronics. In particular, the quantum anomalous Hall (QAH) effect in magnetic 2D layers shows a very promising prospect for hosting Majorana zero modes at the topologically protected edge states in proximity to superconductors. However, the QAH effect has not yet been experimentally realized in monolayer systems to date. In this work, we study the electronic structures and topological properties of the 2D ferromagnetic transition-metal dichalcogenides (TMD) monolayer 1T-VSe2 by first-principles calculations with the Heyd-Scuseria-Ernzerhof (HSE) functional. We find that the spin-orbit coupling (SOC) opens a continuous band gap at the magnetic Weyl-like crossing point hosting the quantum anomalous Hall effect with Chern number C=2. Moreover, we demonstrate the topologically protected edge states and intrinsic (spin) Hall conductivity in this magnetic 2D TMD system. Our results indicate that 1T-VSe2 monolayer serves as a stoichiometric quantum anomalous Hall material.
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TL;DR: In this article , the up-to-date advances regarding the syntheses and physical properties of 2D MTMDCs, as well as their multifunctional applications are reviewed.
Abstract: Two-dimensional (2D) metallic transition metal dichalcogenides (MTMDCs) are emerging as an appealing class of materials for a wide range of research topics, including electronics, spintronics, and energy-related fields, in view of their unique physical and chemical properties. Notably, the controlled synthesis of such promising materials is a prerequisite. In this Perspective, we review the up-to-date advances regarding the syntheses and physical properties of 2D MTMDCs, as well as their multifunctional applications. First, a variety of synthetic strategies of 2D MTMDCs, such as chemical exfoliation, chemical vapor transport, atomic layer deposition, molecular beam epitaxy, and chemical vapor deposition, are systematically summarized. Second, the fundamental physical properties of 2D MTMDCs are introduced, including charge density wave order, ferromagnetism, and superconductivity. Third, the versatile applications of 2D MTMDCs in electronic devices and energy-related fields are discussed. Finally, the challenges about the exploration of controlled syntheses, interesting physical issues, and multifunctional applications are highlighted, and future directions are also proposed. We believe that this Perspective is comprehensive and insightful for the controllable syntheses, physical property characterizations, and application exploitations of 2D MTMDCs.
5 citations
TL;DR: In this article , a quasi-1D vdW layered compound CrZr4Te14 is successfully synthesized, where the 1D [CrTe2] and [ZrTe3] chains along the b-axis of the compound showed strong anisotropy of phonon vibrations and magnetism.
Abstract: The discovery of 2D van der Waals (vdW) magnetic materials is of great significance to explore intriguing 2D magnetic physics and develop innovative spintronic devices. In this work, a new quasi‐1D vdW layered compound CrZr4Te14 is successfully synthesized. Owing to the existence of 1D [CrTe2] and [ZrTe3] chains along the b‐axis, CrZr4Te14 crystals show strong anisotropy of phonon vibrations, electrical transport, and magnetism. Density functional theory calculations reveal the ferromagnetic (FM) coupling within the [CrTe2] chain, while the interchain and interlayer couplings are both weakly antiferromagnetic (AF). Notably, a large intrinsic negative magnetoresistance (nMR) of −56% is achieved at 2 K under 9 T, and the in‐plane anisotropic factor of nMR can reach up to 8.2 in the CrZr4Te14 device. The 1D FM chains and anisotropic nMR effect make CrZr4Te14 an interesting platform for exploring novel polarization‐sensitive spintronics.
3 citations
TL;DR: In this paper , the authors investigated the thermoelectric properties of 1T-VSe2/1H-MoSe2van der Waals system and also probe its TE characteristics on the basis of firstprinciple calculations.
Abstract: The correlation between topological and thermoelectrics promotes numerous interesting electronic phenomena and sets the stage for efficient thermopower devices. Herein, we report nontrivial band topology of 1T-VSe2/1H-MoSe2van der Waals system and also probe its thermoelectric (TE) characteristics on the basis of first-principle calculations. The crossover of bands, which creates a close loop near Fermi level along M-K high symmetry points, gets inverted at former crossing points of bands, under spin-orbit coupling effect. The calculated Chern NumberC= 1 supports the nontrivial band topology whereas the broken time reversal symmetry asserts its magnetic Weyl semimetallic behavior. The nontrivial band topology falls under the category of Type-I Weyl band crossing. We delve into the TE characteristics of the proposed topological material by employing constant relaxation time approximation. The heterostructure shows high electrical conductivity of order 106S m-1at both 300 K and 1200 K, and a low magnitude of Seebeck coefficient (S) value of 79.3μV K-1near room temperature. Such interplay between the topological phase and TE characteristics can lay foundation for next-generation topological-TE devices.
2 citations
TL;DR: In this article , a review of 2D chalcogenide-based FM semiconductors is presented, including the basic physical properties, including crystal structures, electronic structures, and mechanical stability.
Abstract: Two-dimensional (2D) magnetic materials draw an enormous amount of attention due to their novel physical properties and potential spintronics device applications. Room-temperature ferromagnetic (FM) semiconductors have long been pursued in 2D magnetic materials, which show a long range magnetic order down to atomic-layer thickness. The intrinsic ferromagnetism has been predicted in a series of 2D materials and verified in experiments and the magnetism can be modulated by multiple physical fields, exhibiting promising application prospects. In this review, we overview several types of 2D chalcogenide-based FM semiconductors discovered in recent years. We summary and compare their basic physical properties, including the crystal structures, electronic structures, and mechanical stability. The 2D magnetism can be described by several physical models. We also focus on the recent progresses about theoretical prediction of FM semiconductors and experimental observation of external-field regulation. Most of investigations have shown that 2D chalcogenide-based FM semiconductors have relatively high Curie temperature (Tc) and structural stability. These materials are promising to realize the room-temperature ferromagnetism in atomic-layer thickness, which is significant to design spintronics devices.
1 citations
TL;DR: In this paper , a scheme to explore the experimental signature from parity anomaly in the measurement of optical Hall conductivity was proposed, which revealed the appearance of half-quantized Hall conductivities in low or high-frequency regimes.
Abstract: Parity anomaly is a quantum mechanical effect that the parity symmetry in a two-dimensional classical action is failed to be restored in any regularization of the full quantum theory and is characterized by a half-quantized Hall conductivity. Here we propose a scheme to explore the experimental signature from parity anomaly in the measurement of optical Hall conductivity, in which the optical Hall conductivity is nearly half quantized for a proper range of frequency. The behaviors of optical Hall conductivity are studied for several models, which reveal the appearance of half-quantized Hall conductivity in low or high-frequency regimes. The optical Hall conductivity can be extracted from the measurement of Kerr and Faraday rotations and the absorption rate of the circularly polarized light. This proposal provides a practical method to explore the signature of parity anomaly in topological quantum materials.
1 citations
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TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.
81,985 citations
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.
47,666 citations
TL;DR: In this article, the quantum spin Hall (QSH) effect can be realized in mercury-cadmium telluride semiconductor quantum wells, a state of matter with topological properties distinct from those of conventional insulators.
Abstract: We show that the quantum spin Hall (QSH) effect, a state of matter with topological properties distinct from those of conventional insulators, can be realized in mercury telluride–cadmium telluride semiconductor quantum wells. When the thickness of the quantum well is varied, the electronic state changes from a normal to an “inverted” type at a critical thickness d c . We show that this transition is a topological quantum phase transition between a conventional insulating phase and a phase exhibiting the QSH effect with a single pair of helical edge states. We also discuss methods for experimental detection of the QSH effect.
5,187 citations
TL;DR: The Z2 order of the QSH phase is established in the two band model of graphene and a generalization of the formalism applicable to multiband and interacting systems is proposed.
Abstract: The quantum spin Hall (QSH) phase is a time reversal invariant electronic state with a bulk electronic band gap that supports the transport of charge and spin in gapless edge states. We show that this phase is associated with a novel Z2 topological invariant, which distinguishes it from an ordinary insulator. The Z2 classification, which is defined for time reversal invariant Hamiltonians, is analogous to the Chern number classification of the quantum Hall effect. We establish the Z2 order of the QSH phase in the two band model of graphene and propose a generalization of the formalism applicable to multiband and interacting systems.
4,973 citations