Two-Dimensional Time-Reversal-Invariant **Topological** **Insulators** via
Fredholm Theory

**topological**invariant, define a new one for the edge, and show their equivalence (the bulk-edge correspondence) via homotopy. Expand abstract.

**topological**invariant, define a new one for the edge, and show their equivalence (the bulk-edge correspondence) via homotopy.

7/10 relevant

arXiv

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

**topological**

**insulators**. Expand abstract.

**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**.

10/10 relevant

arXiv

Pursuing High-Temperature Quantum Anomalous Hall Effect in MnBi$_2$Te$_4$/Sb$_2$Te$_3$ Heterostructures

**topological**

**insulators**or intrinsic magnetic

**topological**

**insulator**MnBi$_2$Te$_4$ by applying an external magnetic field. However, either the low observation temperature or the unexpected external magnetic field (tuning all MnBi$_2$Te$_4$ layers to be ferromagnetic) still hinders further application of QAHE. Here, we theoretically demonstrate that proper stacking of MnBi$_2$Te$_4$ and Sb$_2$Te$_3$ layers is able to produce intrinsically ferromagnetic van der Waals heterostructures to realize the high-temperature QAHE. We find that interlayer ferromagnetic transition can happen at $T_{\rm C}=42~\rm K$ when a five-quintuple-layer Sb$_2$Te$_3$

**topological**

**insulator**is inserted into two septuple-layer MnBi$_2$Te$_4$ with interlayer antiferromagnetic coupling. Band structure and

**topological**property calculations show that MnBi$_2$Te$_4$/Sb$_2$Te$_3$/MnBi$_2$Te$_4$ heterostructure exhibits a topologically nontrivial band gap around 26 meV, that hosts a QAHE with a Chern number of $\mathcal{C}=1$. In addition, our proposed materials system should be considered as an ideal platform to explore high-temperature QAHE due to the fact of natural charge-compensation, originating from the intrinsic n-type defects in MnBi$_2$Te$_4$ and p-type defects in Sb$_2$Te$_3$.

7/10 relevant

arXiv

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

**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.

10/10 relevant

arXiv

Evidence of **topological** gap opening in the surface state of Bi$_2$Se$_3$
by proximity to a magnetic **insulator**

**Topological**

**insulators**are bulk

**insulators**with exotic surface states, protected under time-reversal symmetry, that hold promise in observing many exciting condensed-matter phenomena. In this report, we show that by having a

**topological**

**insulator**(Bi$_2$Se$_3$) in proximity to a magnetic

**insulator**(EuS), a metal-to-

**insulator**transition in the surface state, attributed to opening of an exchange gap, can be observed whose properties are tunable using bottom gate voltage and external magnetic field. Our study provides evidence of gate-controlled enhanced interface magnetism with the signature of half-integer quantum Hall effect when the Fermi level is tuned into the exchange gap. These results pave the way for using magnetic proximity effect in developing

**topological**electronic devices.

7/10 relevant

arXiv

Antiferromagnetic **Topological** **Insulator** MnBi2Te4: Synthesis and Magnetic
properties

**topological**

**insulator**(AFM TI), and will become a promising material to discover exotic

**topologic**al quantum phenomena. Expand abstract.

**topological**

**insulator**(AFM TI), and will become a promising material to discover exotic

**topological**quantum phenomena. In this work, we have realized the successful synthesis of high-quality MnBi2Te4 single crystals by solid-state reactions. The as-grown MnBi2Te4 single crystal exhibits a van der Waals layered structure, which is composed of septuple Te-Bi-Te-Mn-Te-Bi-Te sequences as determined by powder X-ray diffraction (PXRD) and high-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The magnetic order below 25 K as a consequence of A-type antiferromagnetic interaction between Mn layers in the MnBi2Te4 crystal suggests the unique interplay between antiferromagnetism and

**topological**quantum states. The transport measurements of MnBi2Te4 single crystals further confirm its magnetic transition. Moreover, the unstable surface of MnBi2Te4, which is found to be easily oxidized in air, deserves attention for onging research on few-layer samples. This study on the first AFM TI of MnBi2Te4 will guide the future research on other potential candidates in the MBixTey family (M = Ni, V, Ti, etc.).

7/10 relevant

arXiv

Classification of **topological** ladder models

**topological**

**insulators**in novel symmetry classes with ladder architectures. Expand abstract.

**topological**phases of matter. Here we present a classification of ladder models giving rise to

**topological**

**insulators**. We identify six different types of

**topological**ladder models, three in the BDI symmetry class, and three in the AIII symmetry class. They correspond to six distinct configurations of Wilson fermions. The six types are manifested in distinctive momentum distributions of the corresponding

**topological**edge modes. The number of Wilson fermions, their chirality and mass, are directly manifested in the number, momentum and height of the peaks of the momentum distribution of the corresponding

**topological**edge modes. We identify a canonical ladder geometry, the {\em bowtie ladder}, from which any other

**topological**ladder model can be obtained by a unitary transformation. We identify, classify and list all possible

**topological**ladder geometries, determining the parameter regimes in which each of the six types of

**topological**edge modes can be realized. Our results open a route for the experimental realization and detection of

**topological**

**insulators**in novel symmetry classes with ladder architectures.

5/10 relevant

arXiv

Anomalously large spin-current voltages on the surface of SmB$_6$

**topological**

**insulators**have attracted interest both from a fundamental and applied point of view. A recent proposal describes a method of probing these surface states with ferromagnetic contacts, which was subsequently applied to a variety of materials. In this study, we use this method on the potential

**topological**

**insulator**SmB$_6$ with a new design based on the Corbino geometry. Though the signal behaves as predicted for all orientations of current and magnetic field, its magnitude is much larger than expected. Possible parasitic effects such as stray field-induced Hall voltages are excluded, leaving the origin of the observations uncertain. This corroborates the need for careful analysis when interpreting results of similar experiments.

6/10 relevant

arXiv

Interplay of Dirac nodes and Volkov-Pankratov surface states in compressively strained HgTe

**topological**

**insulators**, HgTe provides the archetypical reference for the experimental investigation of

**topologic**al semimetals. Expand abstract.

**topological**insulators, Dirac and Weyl semimetals have become a pivotal direction of research in contemporary condensed matter physics. While a detailed accessible conception exists from a theoretical viewpoint, these

**topological**semimetals pose a serious challenge in terms of experimental synthesis and analysis to allow for their unambiguous identification. In this work, we report on detailed transport experiments on compressively strained HgTe. Due to the superior sample quality in comparison to other

**topological**semimetallic materials, this enables us to resolve the interplay of

**topological**surface states and semimetallic bulk states to an unprecedented degree of precision and complexity. As our gate design allows us to precisely tune the Fermi level at the Weyl and Dirac points, we identify a magnetotransport regime dominated by Weyl/Dirac bulk state conduction for small carrier densities and by

**topological**surface state conduction for larger carrier densities. As such, similar to

**topological**insulators, HgTe provides the archetypical reference for the experimental investigation of

**topological**semimetals.

5/10 relevant

arXiv

Non-local electrical detection of spin-momentum-locked surface currents
in the 3D **topological** **insulator** BiSbTeSe$_{2}$

**topological**

**insulators**offer unique transport characteristics which make them distinguishable from trivial conductors. Due to the

**topological**protection, these states are gapless over the whole surface of the material. Here, we detect the surface states in the

**topological**

**insulator**BiSbTeSe$_{2}$ by electrical means using a non-local transport configuration. We unambiguously probe the spin-momentum locking of the topologically protected surface states by spin-sensitive electrical read-out using ferromagnetic Co/Al$_2$O$_3$ electrodes. We show that the non-local measurement allows to probe the surface currents flowing along the whole surface, i.e. from the top along the side to the bottom surface and back to the top surface along the opposite side. This is in contrast to local transport configurations where only the surface states of the one face being in contact to the electrodes can be measured. Our results furthermore exclude the contribution of the bulk to the non-local transport at low temperatures. Increasing the temperature, on the other hand, increases the interaction between bulk and surface states, which shortens the non-local current path along the surface and hence leads to a complete disappearance of the non-local signal at around 20 K. All this demonstrates that the non-local signal at low temperatures is solely due to the topologically protected surface states.

10/10 relevant

arXiv