Antiferromagnetic topological crystalline insulator and mixed Weyl semimetal in two-dimensional NpAs monolayer

Abstract Magnetic topological states have attracted significant attentions due to their intriguing quantum phenomena and potential applications in topological spintronic devices. Here, we propose a two-dimensional material NpAs monolayer as a candidate for multiple topological states accompanied with the changes of magnetic structures. Under the antiferromagnetic configuration, the long-awaited topological crystalline insulator (TCI) emerges with a nonzero mirror Chern number $\mathcal{C_M} = 1$ and a giant band gap of 630 meV, and remarkably a pair of gapless edge states can be tailored by rotating the magnetization directions while the TCI phase survives. Moreover, we establish the existence of quantum anomalous Hall effect and nontrivial nodal points under the ferromagnetic configuration, thereby giving rise to the mixed Weyl semimetal after adding the magnetization direction to topological classification. Our findings not only provide an ideal candidate for uncovering exotic topological characters with magnetism but also put forward potential applications in topological spintronics.

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Novel topological states of nodal points and nodal rings in 2D planar octagon TiB4

Nanoscale ◽

10.1039/d0nr08015b ◽

2021 ◽

Vol 13 (5) ◽

pp. 3194-3200

Author(s):

Weizhen Meng ◽

Wei Liu ◽

Xiaoming Zhang ◽

Ying Liu ◽

Xuefang Dai ◽

...

Keyword(s):

2D Materials ◽

Topological States Of Matter ◽

Two Dimensional ◽

Nodal Points ◽

Potential Applications ◽

Topological States

Topological states of matter in two-dimensional (2D) materials have received increasing attention due to their potential applications in nanoscale spintronics.

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Twisted bulk-boundary correspondence of fragile topology

Science ◽

10.1126/science.aaz7650 ◽

2020 ◽

Vol 367 (6479) ◽

pp. 794-797 ◽

Cited By ~ 12

Author(s):

Zhi-Da Song ◽

Luis Elcoro ◽

B. Andrei Bernevig

Keyword(s):

Boundary Conditions ◽

Topological Insulator ◽

Experimental Verification ◽

Real Space ◽

Two Dimensional ◽

Edge States ◽

Quantum Numbers ◽

Boundary Correspondence ◽

Topological States ◽

Twisted Boundary Conditions

A topological insulator reveals its nontrivial bulk through the presence of gapless edge states: This is called the bulk-boundary correspondence. However, the recent discovery of “fragile” topological states with no gapless edges casts doubt on this concept. We propose a generalization of the bulk-boundary correspondence: a transformation under which the gap between the fragile phase and other bands must close. We derive specific twisted boundary conditions (TBCs) that can detect all the two-dimensional eigenvalue fragile phases. We develop the concept of real-space invariants, local good quantum numbers in real space, which fully characterize these phases and determine the number of gap closings under the TBCs. Realizations of the TBCs in metamaterials are proposed, thereby providing a route to their experimental verification.

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Coverage-dependent magnetic and electronic properties of graphene with Co adatoms

International Journal of Modern Physics C ◽

10.1142/s0129183121501655 ◽

2021 ◽

pp. 2150165

Author(s):

Min Gao ◽

Jun Hu

Keyword(s):

Electronic Properties ◽

First Principles ◽

Dirac Point ◽

2D Materials ◽

Anomalous Hall Effect ◽

Spin Moment ◽

Two Dimensional ◽

First Principles Calculations ◽

Spin Polarized ◽

Topological States

Decorating two-dimensional (2D) materials with transition-metal adatoms is an effective way to bring about new physical properties that are intriguing for applications in electronics and spintronics devices. Here, we systematically studied the coverage-dependent magnetic and electronic properties of graphene decorated by Co adatoms, based on first-principles calculations. We found that if the Co coverage is larger than 1/3[Formula: see text]ML, the Co atoms will aggregate to form a Co monolayer and then a van der Waals bilayer system between the Co monolayer and graphene forms. When the Co coverage is [Formula: see text][Formula: see text]ML, the Co adatom is spin-polarized with spin moment varying from 1.1 to 1.4[Formula: see text][Formula: see text]. The [Formula: see text] and [Formula: see text] orbitals of Co hybridize significantly with the [Formula: see text] bands of graphene, which generates a series of new bands in the energy range from [Formula: see text][Formula: see text]eV to 1[Formula: see text]eV with respect to the Dirac point of graphene. In most cases, the new bands near the Fermi level lead to topological states characterized by the quantum anomalous Hall effect.

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Demonstration of a third-order hierarchy of topological states in a three-dimensional acoustic metamaterial

Science Advances ◽

10.1126/sciadv.aay4166 ◽

2020 ◽

Vol 6 (13) ◽

pp. eaay4166 ◽

Cited By ~ 13

Author(s):

Matthew Weiner ◽

Xiang Ni ◽

Mengyao Li ◽

Andrea Alù ◽

Alexander B. Khanikaev

Keyword(s):

Three Dimensional ◽

Surface States ◽

Three Dimensions ◽

Dimensional System ◽

Edge States ◽

Third Order ◽

Acoustic Metamaterial ◽

Boundary States ◽

Topological States ◽

Quantum Phenomena

Classical wave systems have constituted an excellent platform for emulating complex quantum phenomena, such as demonstrating topological phenomena in photonics and acoustics. Recently, a new class of topological states localized in more than one dimension of a D-dimensional system, referred to as higher-order topological (HOT) states, has been reported, offering an even more versatile platform to confine and control classical radiation and mechanical motion. Here, we design and experimentally study a 3D topological acoustic metamaterial supporting third-order (0D) topological corner states along with second-order (1D) edge states and first-order (2D) surface states within the same topological bandgap, thus establishing a full hierarchy of nontrivial bulk polarization–induced states in three dimensions. The assembled 3D topological metamaterial represents the acoustic analog of a pyrochlore lattice made of interconnected molecules, and is shown to exhibit topological bulk polarization, leading to the emergence of boundary states.

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Ferromagnetic dual topological insulator in a two-dimensional honeycomb lattice

Materials Horizons ◽

10.1039/d0mh00803f ◽

2020 ◽

Vol 7 (9) ◽

pp. 2431-2438

Author(s):

Hao Wang ◽

Ning Mao ◽

Chengwang Niu ◽

Shiying Shen ◽

Myung-Hwan Whangbo ◽

...

Keyword(s):

Hall Effect ◽

Topological Insulator ◽

Topological Insulators ◽

Anomalous Hall Effect ◽

Topological Invariant ◽

Honeycomb Lattice ◽

Two Dimensional ◽

Edge States ◽

Quantum Anomalous Hall Effect ◽

Significant Attention

Magnetic topological insulators (TIs), including the quantum anomalous Hall effect and antiferromagnetic TIs, have attracted significant attention owing to the exotic properties they give rise to, however, ferromagnetic TIs with gapless surface/edge states and a nonzero topological invariant have not been reported so far.

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Quantum Spin Hall Insulators and Topological Rashba-splitting Edge States in Two-dimensional CX3 (X=Sb, Bi)

Physical Chemistry Chemical Physics ◽

10.1039/d0cp05374k ◽

2020 ◽

Author(s):

Shanshan Wang ◽

Wencong Sun ◽

Shuai Dong

Keyword(s):

First Principles ◽

Condensed Matter ◽

Electronic Devices ◽

Quantum Spin ◽

Two Dimensional ◽

Edge States ◽

First Principles Calculations ◽

Topological Materials ◽

Potential Applications ◽

High Carrier

Two-dimensional topological materials inspired intense interest in condensed matter physics due to their high carrier mobilities and potential applications in electronic devices. Here, based on first-principles calculations, we found that...

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Spin-filtered edge states with an electrically tunable gap in a two-dimensional topological crystalline insulator

Nature Materials ◽

10.1038/nmat3828 ◽

2013 ◽

Vol 13 (2) ◽

pp. 178-183 ◽

Cited By ~ 201

Author(s):

Junwei Liu ◽

Timothy H. Hsieh ◽

Peng Wei ◽

Wenhui Duan ◽

Jagadeesh Moodera ◽

...

Keyword(s):

Two Dimensional ◽

Edge States ◽

Topological Crystalline Insulator

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Reconfigurable Topological Phases in Two-Dimensional Dielectric Photonic Crystals

Crystals ◽

10.3390/cryst9040221 ◽

2019 ◽

Vol 9 (4) ◽

pp. 221 ◽

Cited By ~ 1

Author(s):

Hongbo Huang ◽

Shaoyong Huo ◽

Jiujiu Chen

Keyword(s):

Photonic Crystals ◽

Lattice Structure ◽

Topological Defects ◽

Topological Phases ◽

Two Dimensional ◽

Edge States ◽

Microwave Frequencies ◽

Potential Applications ◽

Microwave Photon ◽

Elliptical Cylinders

The extensive research on photonic topological insulators has opened up an intriguing way to control electromagnetic (EM) waves. In this work, we numerically demonstrate reconfigurable microwave photon analogues of topological insulator (TIs) in a triangular lattice of elliptical cylinders, according to the theory of topological defects. Multiple topological transitions between the trivial and nontrivial photonic phases can be realized by inhomogeneously changing the ellipse orientation, without altering the lattice structure. Topological protection of the edge states and reconfigurable topological one-way propagation at microwave frequencies, are further verified. Our approach provides a new route towards freely steering light propagations in dielectric photonic crystals (PCs), which has potential applications in the areas of topological signal processing and sensing.

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Strain-Induced Quantum Spin Hall Effect in Two-Dimensional Methyl-Functionalized Silicene SiCH3

Nanomaterials ◽

10.3390/nano8090698 ◽

2018 ◽

Vol 8 (9) ◽

pp. 698 ◽

Cited By ~ 4

Author(s):

Ceng-Ceng Ren ◽

Wei-Xiao Ji ◽

Shu-Feng Zhang ◽

Chang-Wen Zhang ◽

Ping Li ◽

...

Keyword(s):

Hexagonal Boron Nitride ◽

Quantum Spin ◽

Honeycomb Lattice ◽

Potential Candidate ◽

Two Dimensional ◽

Edge States ◽

Spin Orbital ◽

Spintronic Devices ◽

Potential Applications ◽

Quantum Spin Hall

Quantum Spin Hall (QSH) has potential applications in low energy consuming spintronic devices and has become a researching hotspot recently. It benefits from insulators feature edge states, topologically protected from backscattering by time-reversal symmetry. The properties of methyl functionalized silicene (SiCH3) have been investigated using first-principles calculations, which show QSH effect under reasonable strain. The origin of the topological characteristic of SiCH3, is mainly associated with the s-pxy orbitals band inversion at Γ point, whilst the band gap appears under the effect of spin-orbital coupling (SOC). The QSH phase of SiCH3 is confirmed by the topological invariant Z2 = 1, as well as helical edge states. The SiCH3 supported by hexagonal boron nitride (BN) film makes it possible to observe its non-trivial topological phase experimentally, due to the weak interlayer interaction. The results of this work provide a new potential candidate for two-dimensional honeycomb lattice spintronic devices in spintronics.

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