Found 354 results, sorted by relevancy. Show newest relevant.Update me on new preprints

The hybrid-order topology of weak **topological** **insulators**

Considering the minimal symmetry requirements, we anticipate that our findings could apply to a large number of weak

**topological****insulators**. Expand abstract. We consider weak

**topological****insulators**with a twofold rotation symmetry around the dark direction, and show that these systems can be endowed with the**topological**crystalline structure of a higher-order**topological****insulator**protected by rotation symmetry. These hybrid-order weak**topological****insulators**display surface Dirac cones on all surfaces. Translational symmetry breaking perturbations gap the Dirac cones on the side surfaces leaving anomalous helical hinge modes behind. We also prove that the existence of this**topological**phase comes about due to a hidden crystalline**topological**invariant of quantum spin-Hall**insulators**that can neither be revealed by symmetry indicators nor using Wilson loop invariants. Considering the minimal symmetry requirements, we anticipate that our findings could apply to a large number of weak**topological****insulators**.132 days ago

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arXiv

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arXiv

Pure spin current devices based on ferromagnetic **topological** **insulators**

We investigate heterostuctures of

**topological****insulators**and ferromagnetic**topologic**al**insulator**s by means of numerical transport calculations. Expand abstract. Two-dimensional

**topological****insulators**possess two counter propagating edge channels with op- posite spin direction. Recent experimental progress allowed to create ferromagnetic**topological****insulators**realizing a quantum anomalous Hall (QAH) state. In the QAH state one of the two edge channels disappears due to the strong ferromagnetic exchange field. We investigate heterostuctures of**topological****insulators**and ferromagnetic**topological****insulators**by means of numerical transport calculations. We show that spin current flow in such heterostructures can be controlled with high fidelity. Specifically, we propose spintronic devices that are capable of creating, switching and de- tecting pure spin currents using the same technology. In these devices electrical currents are directly converted into spin currents, allowing a high conversion efficiency. Energy independent transport properties in combination with large bulk gaps in some**topological****insulator**materials may allow operation even at room temperature.1290 days ago

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arXiv

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arXiv

Modulation of crystal and electronic structures in **topological** **insulators** by rare-earth doping

Our results hold potential for the realization of exotic

**topological**effects in magnetic**topologic**al**insulators**. Expand abstract.We study magnetotransport in a rare earth doped

**topological**insulator, Sm0.1Sb1.9Te3 single crystals, under magnetic fields up to 14 T. It is found that that the crystals exhibit Shubnikov de Haas oscillations in their magneto-transport behaviour at low temperatures and high magnetic fields. The SdH oscillations result from the mixed contributions of bulk and surface states. We also investigate the SdH oscillations in different orientations of the magnetic field, which reveals a three dimensional Fermi surface topology. By fitting the oscillatory resistance with the Lifshitz Kosevich theory, we draw a Landau-level fan diagram that displays the expected nontrivial phase. In addition, the density functional theory calculations shows that Sm doping changes the crystal structure and electronic structure compared with pure Sb2Te3. This work demonstrates that rare earth doping is an effective way to manipulate the Fermi surface of**topological****insulators**. Our results hold potential for the realization of exotic**topological**effects in magnetic**topological****insulators**.156 days ago

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arXiv

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arXiv

Screening potential **topological** **insulators** in half-Heusler compounds via compressed-sensing

Beyond the finite training data, the proposed descriptor is employed to screen many new half-Heusler compounds, including those with integer and fractional stoichiometry, and a larger number of possible

**topological****insulators**are predicted. Expand abstract.Ternary half-Heusler compounds with widely tunable electronic structures, present a new platform to discover

**topological****insulators**. Due to time-consuming computations and synthesis procedures, the identification of new**topological****insulators**is however a rough task. Here, we adopt a compressed-sensing approach to rapid screen potential**topological****insulators**in half-Heusler family, which is realized via a two-dimensional descriptor that only depends on the fundamental properties of the constituent atoms. Beyond the finite training data, the proposed descriptor is employed to screen many new half-Heusler compounds, including those with integer and fractional stoichiometry, and a larger number of possible**topological****insulators**are predicted.256 days ago

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arXiv

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arXiv

Higher-order **topological** **insulators** in synthetic dimensions

Here we construct photonic higher-order

**topological****insulators**(PHOTI) in synthetic dimensions. Expand abstract. Conventional

**topological****insulators**support boundary states that have one dimension lower than the bulk system that hosts them, and these states are topologically protected due to quantized bulk dipole moments. Recently, higher-order**topological****insulators**have been proposed as a way of realizing**topological**states that are two or more dimensions lower than the bulk, due to the quantization of bulk quadrupole or octupole moments. However, all these proposals as well as experimental realizations have been restricted to real-space dimensions. Here we construct photonic higher-order**topological****insulators**(PHOTI) in synthetic dimensions. We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension, where each photonic molecule comprises two coupled rings. By changing the phase difference of the modulation between adjacently coupled photonic molecules, we predict a dynamical**topological**phase transition in the PHOTI. Furthermore, we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a 4th order hexadecapole (16-pole) insulator, supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.17 days ago

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arXiv

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arXiv

Finite-dimensional bistable **topological** **insulators**: From small to large

In this work using as an example realistic polariton

**topological****insulators**built from small-size honeycomb arrays of microcavity pillars, we illustrate how**topologic**al properties of the system build up upon gradual increase of its dimensionality. Expand abstract. Photonic

**topological****insulators**supporting unidirectional topologically protected edge states represent attractive platform for realization of disorder- and backscattering-immune transport of edge excitations in both linear and nonlinear regimes. In many realizations of**topological****insulators**structured periodic materials are used, since they may admit specific Dirac degeneracy in the spectrum, around which unidirectional edge states appear under the action of physical effects breaking time-reversal symmetry. While properties of the edge states at unclosed interfaces of two bulk media with different topology are known, the existence of the edge states in practical finite-dimensional**topological****insulators**fully immersed in nontopological environment remains largely unexplored. In this work using as an example realistic polariton**topological****insulators**built from small-size honeycomb arrays of microcavity pillars, we illustrate how**topological**properties of the system build up upon gradual increase of its dimensionality. To account for dissipative nature of polariton condensate forming in the array of microcavity pillars, we consider the impact of losses and resonant pump leading to rich bistability effects in this system. We describe the mechanism in accordance with which trivial-phase pump "selects" and excites specific nonlinear**topological**edge states circulating along the periphery of the structure in the azimuthal direction dictated by the direction of the external applied magnetic field. We also show the possibility of utilization of vortex pump with different**topological**charges for selective excitation of different edge currents.35 days ago

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arXiv

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arXiv

Theory of current-driven dynamics of spin textures on a surface of
**topological** **insulators**

Spin-transfer torque is one of the important physical quantities to understand for successful application of topological insulators to spintronics. Expand abstract.

Spin-transfer torque is one of the important physical quantities to understand for successful application of

**topological****insulators**to spintronics. In this paper, we present analytical expressions of the spin-transfer torques on a surface of a magnetic**topological****insulator**by including the higher-order contributions of momentum, $k^2$-term and the hexagonal warping. We obtain six different types of the spin-transfer torque including both the field-like and the damping-like torques; the four of them appear only when the higher-order momentum contributions are included. In addition, we discuss the dynamics of magnetic skyrmions driven by the spin-transfer torques on the surface of the**topological****insulator**. Unlike the skyrmion dynamics in conventional metals, we find that the dynamics significantly depends on the internal structure of magnetic textures.134 days ago

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arXiv

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arXiv

Commuting-projector Hamiltonians for 2D **topological** **insulators**: edge
physics and many-body invariants

Inspired by a recently constructed commuting-projector Hamiltonian for a two-dimensional (2D) time-reversal-invariant topological superconductor [Wang et al., Phys. Expand abstract.

Inspired by a recently constructed commuting-projector Hamiltonian for a two-dimensional (2D) time-reversal-invariant

**topological**superconductor [Wang et al., Phys. Rev. B 98, 094502 (2018)], we introduce a commuting-projector model that describes an interacting yet exactly solvable 2D**topological****insulator**. We explicitly show that both the gapped and gapless boundaries of our model are consistent with those of band-theoretic, weakly interacting**topological****insulators**. Interestingly, on certain lattices our time-reversal-symmetric models also enjoy $\mathcal{CP}$ symmetry, leading to intuitive interpretations of the bulk invariant for a $\mathcal{CP}$-symmetric**topological****insulator**upon putting the system on a Klein bottle. We also briefly discuss how these many-body invariants may be able to characterize models with only time-reversal symmetry.165 days ago

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arXiv

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arXiv

Type-II quadrupole **topological** **insulators**

The existence of the new

**topological**insulating phase means that new multipole**topologic**al**insulators**with distinct properties can exist in broader contexts beyond classical constraints. Expand abstract. Modern theory of electric polarization is formulated by the Berry phase, which, when quantized, leads to

**topological**phases of matter. Such a formulation has recently been extended to higher electric multipole moments, through the discovery of the so-called quadupole**topological****insulator**. It has been established by a classical electromagnetic theory that in a two-dimensional material the quantized properties for the quadupole**topological****insulator**should satisfy a basic relation. Here we discover a new type of quadupole**topological****insulator**(dubbed as type-II) that violates this relation due to the breakdown of a previously established theory that a Wannier band and an edge energy spectrum are topologically equivalent in a closed quantum system. We find that, similar to the previously discovered (referred to as type-I) quadrupole**topological**insulator, the type-II hosts topologically protected corner states carrying fractional corner charges. However, the edge polarizations only occur at a pair of boundaries in the type-II insulating phase, leading to the violation of the classical constraint. We propose an experimental scheme to realize such a new**topological**phase of matter. The existence of the new**topological**insulating phase means that new multipole**topological****insulators**with distinct properties can exist in broader contexts beyond classical constraints.64 days ago

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arXiv

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arXiv

Layered Photonic **Topological** **Insulators**

Layered photonic

**topological****insulators**not only offer a route towards the observation of richer nontrivial phases, but also open a way for device applications in integrated photonics and information processing by using the additional layer pseudospin. Expand abstract. The recent realization of photonic

**topological****insulators**has brought the discovery of fundamentally new states of light and revolutionary applications such as non-reciprocal devices for photonic diodes and robust waveguides for light routing. The spatially distinguished layer pseudospin has attracted attention in two-dimensional electronic materials. Here we report layered photonic**topological****insulators**based on all-dielectric bilayer photonic crystal slabs. The introduction of layer pseudospin offers more dispersion engineering capability, leading to the layer-polarized and layer-mixed photonic**topological****insulators**. Their phase transition is demonstrated with a model Hamiltonian by considering the nonzero interlayer coupling. Layer-direction locking behavior is found in layer-polarized photonic**topological****insulators**. High transmission is preserved in the bilayer domain wall between two layer-mixed photonic**topological**insulators, even when a large defect is introduced. Layered photonic**topological****insulators**not only offer a route towards the observation of richer nontrivial phases, but also open a way for device applications in integrated photonics and information processing by using the additional layer pseudospin.356 days ago

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arXiv

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arXiv