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

**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.

**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.

10/10 relevant

arXiv

Electronic transport in one-dimensional Floquet **topological** **insulators**
via **topologic**al- and non-topological edge states

**topological**phase diagram of one-dimensional Floquet

**topologic**al

**insulators**with Rashba spin-orbit interaction [Kennes \emph{et al.}, Phys. Expand abstract.

**topological**phase diagram of one-dimensional Floquet

**topological**

**insulators**with Rashba spin-orbit interaction [Kennes \emph{et al.}, Phys. Rev. B {\bf 100}, 041104(R) (2019)]. Using the Keldysh-Floquet formalism, we compute electronic transport properties of these nanowires, where we propose to couple the leads in such a way, as to primarily address electronic states with a large relative weight at one edge of the system. By tuning the Fermi energy of the leads to the center of the

**topological**gap, we are able to directly address the

**topological**edge states, granting experimental access to the

**topological**phase diagram. Surprisingly, we find conductance values similar or even larger in magnitude to those corresponding to

**topological**edge states, when tuning the lead Fermi energy to special values in the bulk, which coincide with bifurcation points of the dispersion relation in complex quasimomentum space. These peaks reveal the presence of narrow bands of states whose wave functions are linear combinations of delocalized bulk states and exponentially localized edge states, where the amplitude of the edge-state component is sharply peaked at the aforementioned bifurcation point, resulting in an unusually large relative edge-weight. We discuss the transport properties of these \emph{non-

**topological**edge states} and explain their emergence in terms of an intuitive yet quantitative physical picture. The mechanism giving rise to these states is not specific to the model we consider here, suggesting that they may be present in a wide class of systems.

10/10 relevant

arXiv

Influence of point defects on the electronic and **topological** properties
of monolayer WTe$_2$

**topological**insulators, such as graphene and WTe$_2$, band inversion originates from chemical bonding and space group symmetry, in contrast to materials such as Bi$_2$Se$_3$, where the band inversion derives from relativistic effects in the atoms. In the former, band inversion is susceptible to changes of the chemical environment, e.g. by defects, while the latter are less affected by defects due to the larger energy scale associated with atomic relativistic effects. Motivated by recent experiments, we study the effect of Te-vacancies and Te-adatoms on the electronic properties of WTe$_2$. We find that the Te-vacancies have a formation energy of $2.21$ eV, while the formation energy of the Te-adatoms is much lower with $0.72$ eV. The vacancies strongly influence the band structure and we present evidence that band inversion is already reversed at the nominal composition of WTe$_{1.97}$. In contrast, we show that the adatoms do not change the electronic structure in the vicinity of the Fermi level and thus the

**topological**properties. Our findings indicate that Te-adatoms should be present in thin films that are grown in a Te-rich environment, and we suggest that they have been observed in scanning tunneling microscopy experiments.

4/10 relevant

arXiv

Efficient spin-orbit torque switching with non-epitaxial chalcogenide heterostructures

**topological**

**insulators**(TIs) have gained increasing attention in recent years. These TIs, which are typically formed by epitaxially grown chalcogenides, possess extremely high SOT efficiencies and have great potential to be employed in the next-generation spintronics devices. However, epitaxy of these chalcogenides is required to ensure the existence of topologically-protected surface state (TSS), which limits the feasibility of using these materials in industry. In this work, we show that non-epitaxial Bi$_{x}$Te$_{1-x}$/ferromagnet heterostructures prepared by conventional magnetron sputtering possess giant SOT efficiencies even without TSS. Through harmonic voltage measurement and hysteresis loop shift measurement, we find that the damping-like SOT efficiencies originated from the bulk spin-orbit interactions of such non-epitaxial heterostructures can reach values greater than 100% at room temperature. We further demonstrate current-induced SOT switching in these Bi$_{x}$Te$_{1-x}$-based heterostructures with thermally stable ferromagnetic layers, which indicates that such non-epitaxial chalcogenide materials can be potential efficient SOT sources in future SOT magnetic memory devices.

4/10 relevant

arXiv

Giant unidirectional magnetoresistance in **topological** **insulator** --
ferromagnetic semiconductor heterostructures

**topological**

**insulator**-- GaMnAs ferromagnetic semiconductor. We obtained a large UMR ratio of 1.1%, and found that this giant UMR is governed not by the giant magnetoresistance (GMR)-like spin-dependent scattering, but by magnon emission/absorption and strong spin-disorder scattering in the GaMnAs layer. Our results provide new insight into the complex physics of UMR, as well as a strategy for enhancing its magnitude for device applications.

7/10 relevant

arXiv

Lateral lattice coherence lengths in thin films of bismuth telluride
**topological** **insulators**, with overview on polarization factors for X-ray
dynamical diffraction in monochromator crystals

**Topological**Insulators(J. Phys. Chem. C 2019, 123, 24818-24825, doi: 10.1021/acs.jpcc.9b05377), several topics on X-ray diffraction analysis of thin films were developed or revisited. A simple equation to determine lateral lattice coherence lengths in thin films stands as the main development (section S4 - Lateral lattice coherence length in thin films), while X-ray dynamical diffraction simulation in monochromator crystals stands as an interesting overview on how the ratio between $\pi$ and $\sigma$ polarization components is affected by whether diffraction takes place under kinematical or dynamical regime (section S3 - Polarization factor).

8/10 relevant

arXiv

**Topological** **Insulators** beyond Energy Band Characterization

**topological**phases beyond conventional energy band characterization. Expand abstract.

**Topological**phases of matter are generally characterized by

**topological**properties of energy bands of a system. Their transitions under preserved symmetries occur through closing a gap of energy bands, leading to topologically protected edge states in energy spectra in

**topological**phases. Here we predict a new

**topological**phase that emerges through closing a gap of bands constructed by energy bands, instead of through closing an energy gap with preserved symmetries. From this perspective,

**topological**phases may arise from

**topological**properties of the "bands of bands" associated with their gap closure and corresponding edge states. We demonstrate this idea by studying a tight-binding model. We find that the Wannier bands constructed by energy bands exhibit a gap closure associated with a change of a winding number, while the energy bands remain gapped and trivial without any zero energy modes. In addition, the

**topological**Wannier bands give rise to quantized edge polarizations. Since the emergence of this

**topological**phase does not involve any energy gap closure, we expect its appearance under unitary time evolution. Indeed, this phase appears as we perform a quench dynamics. Our study opens a new direction for exploring

**topological**phases beyond conventional energy band characterization.

8/10 relevant

arXiv

Variety of magnetic **topological** phases in the
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_m$ family

**topological**

**insulators**(MTIs) featuring quantum anomalous Hall and axion

**insulator**phases. Feasibility of many novel phenomena that \emph{intrinsic} magnetic TIs may host depends crucially on our ability to engineer and efficiently tune their electronic and magnetic structures. Here, using angle- and spin-resolved photoemission spectroscopy along with \emph{ab initio} calculations we report on a large family of intrinsic magnetic TIs in the homologous series of the van der Waals compounds (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_m$ with $m=0, ..., 6$. Magnetic, electronic and, consequently,

**topological**properties of these materials depend strongly on the $m$ value and are thus highly tunable. The antiferromagnetic (AFM) coupling between the neighboring Mn layers strongly weakens on moving from MnBi2Te4 (m=0) to MnBi4Te7 (m=1), changes to ferromagnetic (FM) one in MnBi6Te10 (m=2) and disappears with further increase in m. In this way, the AFM and FM TI states are respectively realized in the $m=0,1$ and $m=2$ cases, while for $m \ge 3$ a novel and hitherto-unknown topologically-nontrivial phase arises, in which below the corresponding critical temperature the magnetizations of the non-interacting 2D ferromagnets, formed by the \MBT\, building blocks, are disordered along the third direction. The variety of intrinsic magnetic TI phases in (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_m$ allows efficient engineering of functional van der Waals heterostructures for

**topological**quantum computation, as well as antiferromagnetic and 2D spintronics.

4/10 relevant

arXiv

Persistent gapless surface states in MnBi2Te4/Bi2Te3 superlattice
antiferromagnetic **topological** **insulator**

**topological**

**insulator**MnBi2Te4 that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Expand abstract.

**topological**quantum materials (TQMs) provide a fertile ground for the emergence of fascinating

**topological**magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic (AFM)

**topological**

**insulator**MnBi2Te4 that could realize quantized anomalous Hall effect and axion

**insulator**phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound MnBi4Te7 where Bi2Te3 and MnBi2Te4 layers alternate to form a superlattice. Using spatial- and angle-resolved photoemission spectroscopy, we identified ubiquitous (albeit termination dependent)

**topological**electronic structures from both Bi2Te3 and MnBi2Te4 terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the

**topological**surface states show little temperature dependence and remain gapless across the AFM transition. The detailed electronic structure of MnBi4Te7 and its temperature evolution, together with the results of its sister compound MnBi2Te4, will not only help understand the exotic properties of this family of magnetic TQMs, but also guide the design for possible applications.

7/10 relevant

arXiv

Terahertz tuning of Dirac plasmons in Bi$_2$Se$_3$ **Topological** **Insulator**

**Topological**Insulators, where massless fermions show a naturally non-linear optical behavior in the terahertz range. The strong interaction scenario has been considered so far from the point of view of light. In this paper, we investigate instead the effect of strong interaction on the plasmon itself. In particular, we will show that Dirac plasmons in Bi$_2$Se$_3$

**Topological**

**Insulator**are strongly renormalized when excited by high-intensity terahertz radiation by displaying a huge red-shift down to 60% of its characteristic frequency. This opens the road towards tunable terahertz non-linear optical devices based on

**Topological**

**Insulators**.

10/10 relevant

arXiv