scholarly journals Topological Bloch bands in graphene superlattices

2015 ◽  
Vol 112 (35) ◽  
pp. 10879-10883 ◽  
Author(s):  
Justin C. W. Song ◽  
Polnop Samutpraphoot ◽  
Leonid S. Levitov
Keyword(s):  
Boron Nitride ◽  
Hall Effect ◽  
Hexagonal Boron Nitride ◽  
Electrical Response ◽  
Model System ◽  
Topological Properties ◽  
Berry Curvature ◽  
Topological Materials ◽  
Highly Sensitive ◽  
Valley Hall Effect

We outline a designer approach to endow widely available plain materials with topological properties by stacking them atop other nontopological materials. The approach is illustrated with a model system comprising graphene stacked atop hexagonal boron nitride. In this case, the Berry curvature of the electron Bloch bands is highly sensitive to the stacking configuration. As a result, electron topology can be controlled by crystal axes alignment, granting a practical route to designer topological materials. Berry curvature manifests itself in transport via the valley Hall effect and long-range chargeless valley currents. The nonlocal electrical response mediated by such currents provides diagnostics for band topology.

scholarly journals Interface-induced sign reversal of the anomalous Hall effect in magnetic topological insulator heterostructures

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Fei Wang ◽  
Xuepeng Wang ◽  
Yi-Fan Zhao ◽  
Di Xiao ◽  
Ling-Jie Zhou ◽  
...  
Keyword(s):  
Hall Effect ◽  
Electric Fields ◽  
First Principles ◽  
Berry Phase ◽  
Condensed Matter ◽  
Anomalous Hall Effect ◽  
First Principles Calculations ◽  
Sign Reversal ◽  
Berry Curvature ◽  
Topological Materials

AbstractThe Berry phase picture provides important insights into the electronic properties of condensed matter systems. The intrinsic anomalous Hall (AH) effect can be understood as the consequence of non-zero Berry curvature in momentum space. Here, we fabricate TI/magnetic TI heterostructures and find that the sign of the AH effect in the magnetic TI layer can be changed from being positive to negative with increasing the thickness of the top TI layer. Our first-principles calculations show that the built-in electric fields at the TI/magnetic TI interface influence the band structure of the magnetic TI layer, and thus lead to a reconstruction of the Berry curvature in the heterostructure samples. Based on the interface-induced AH effect with a negative sign in TI/V-doped TI bilayer structures, we create an artificial “topological Hall effect”-like feature in the Hall trace of the V-doped TI/TI/Cr-doped TI sandwich heterostructures. Our study provides a new route to create the Berry curvature change in magnetic topological materials that may lead to potential technological applications.

scholarly journals Topological Semimetals in Square-Net Materials

2019 ◽  
Vol 49 (1) ◽  
pp. 185-206 ◽  
Author(s):  
Sebastian Klemenz ◽  
Shiming Lei ◽  
Leslie M. Schoop
Keyword(s):  
Hall Effect ◽  
Electronic Properties ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Nodal Line ◽  
Topological Properties ◽  
Topological Materials ◽  
Integer Quantum Hall Effect ◽  
Integer Quantum ◽  
Topological Semimetals

Many materials crystallize in structure types that feature a square net of atoms. While these compounds can exhibit many different properties, some members of this family are topological materials. Within the square-net-based topological materials, the observed properties are rich, ranging, for example, from nodal-line semimetals to a bulk half-integer quantum Hall effect. Hence, the potential for guided design of topological properties is enormous. Here we provide an overview of the crystallographic and electronic properties of these phases and show how they are linked, with the goal of understanding which square-net materials can be topological, and predict additional examples. We close the review by discussing the experimentally observed electronic properties in this family.

Terahertz optical Hall effect in p-type monolayer hexagonal boron nitride on polycrystalline quartz substrate

2021 ◽  
Author(s):  
Muhammad Bilal ◽  
Wen Xu ◽  
Hua Wen ◽  
Xingjia Cheng ◽  
Yiming Xiao ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Hall Effect ◽  
Hexagonal Boron Nitride ◽  
Quartz Substrate ◽  
Optical Hall Effect ◽  
P Type

scholarly journals Unraveling materials Berry curvature and Chern numbers from real-time evolution of Bloch states

2019 ◽  
Vol 116 (10) ◽  
pp. 4135-4140 ◽  
Author(s):  
Dongbin Shin ◽  
Shunsuke A. Sato ◽  
Hannes Hübener ◽  
Umberto De Giovannini ◽  
Jeongwoo Kim ◽  
...  
Keyword(s):  
Real Time ◽  
Linear Response ◽  
Quantum Spin ◽  
Topological Properties ◽  
Berry Curvature ◽  
Topological Materials ◽  
Chern Numbers ◽  
Nonequilibrium States ◽  
Topological Characteristics ◽  
Topological Character

Materials can be classified by the topological character of their electronic structure and, in this perspective, global attributes immune to local deformations have been discussed in terms of Berry curvature and Chern numbers. Except for instructional simple models, linear response theories have been ubiquitously used in calculations of topological properties of real materials. Here we propose a completely different and versatile approach to obtain the topological characteristics of materials by calculating physical observables from the real-time evolving Bloch states: The cell-averaged current density reveals the anomalous velocities that lead to the conductivity quantum. Results for prototypical cases are shown, including a spin-frozen valley Hall and a quantum anomalous Hall insulator. The advantage of this method is best illustrated by the example of a quantum spin Hall insulator: The quantized spin Hall conductivity is straightforwardly obtained irrespective of the non-Abelian nature in its Berry curvature. Moreover, the method can be extended to the description of real observables in nonequilibrium states of topological materials.

scholarly journals Unconventional Hall effect induced by Berry curvature

2020 ◽  
Vol 7 (12) ◽  
pp. 1879-1885 ◽  
Author(s):  
Jun Ge ◽  
Da Ma ◽  
Yanzhao Liu ◽  
Huichao Wang ◽  
Yanan Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solid State ◽  
Theoretical Analysis ◽  
Hall Effect ◽  
Transport Properties ◽  
Berry Phase ◽  
Phase Effect ◽  
Berry Curvature ◽  
Topological Materials ◽  
Weyl Semimetal

Abstract Berry phase and Berry curvature play a key role in the development of topology in physics and do contribute to the transport properties in solid state systems. In this paper, we report the finding of novel nonzero Hall effect in topological material ZrTe5 flakes when the in-plane magnetic field is parallel and perpendicular to the current. Surprisingly, both symmetric and antisymmetric components with respect to magnetic field are detected in the in-plane Hall resistivity. Further theoretical analysis suggests that the magnetotransport properties originate from the anomalous velocity induced by Berry curvature in a tilted Weyl semimetal. Our work not only enriches the Hall family but also provides new insights into the Berry phase effect in topological materials.

scholarly journals Have Mysterious Topological Valley Currents Been Observed in Graphene Superlattices?

2021 ◽  
Author(s):  
Stephan Roche ◽  
Stephen R. Power ◽  
Branislav K. Nikolic ◽  
José Hugo Garcia ◽  
Antti-Pekka Jauho
Keyword(s):  
Hall Effect ◽  
Critical Discussion ◽  
Berry Curvature ◽  
Nonlocal Transport ◽  
Valley Hall Effect

Abstract We provide a critical discussion concerning the claim of topological valley currents, driven by a global Berry curvature and valley Hall effect proposed in recent litterature. After pointing out a major inconsistency of the theoretical scenario proposed to interpret giant nonlocal resistance, we discuss possible alternative explanations and open directions of research to solve the mystery of nonlocal transport in graphene superlattices.

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