Have Mysterious Topological Valley Currents Been Observed in Graphene Superlattices?

Journal of Physics Materials ◽

10.1088/2515-7639/ac452a ◽

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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Topological Bloch bands in graphene superlattices

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1424760112 ◽

2015 ◽

Vol 112 (35) ◽

pp. 10879-10883 ◽

Cited By ~ 49

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.

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Valley Hall effect and nonlocal transport in strained graphene

2D Materials ◽

10.1088/2053-1583/aa5e9b ◽

2017 ◽

Vol 4 (2) ◽

pp. 024007 ◽

Cited By ~ 13

Author(s):

Xian-Peng Zhang ◽

Chunli Huang ◽

Miguel A Cazalilla

Keyword(s):

Hall Effect ◽

Strained Graphene ◽

Nonlocal Transport ◽

Valley Hall Effect

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

Nature Communications ◽

10.1038/s41467-020-20349-z ◽

2021 ◽

Vol 12 (1) ◽

Cited By ~ 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.

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2D‐Berry‐Curvature‐Driven Large Anomalous Hall Effect in Layered Topological Nodal‐Line MnAlGe

Advanced Materials ◽

10.1002/adma.202006301 ◽

2021 ◽

pp. 2006301

Author(s):

Satya N. Guin ◽

Qiunan Xu ◽

Nitesh Kumar ◽

Hsiang‐Hsi Kung ◽

Sydney Dufresne ◽

...

Keyword(s):

Hall Effect ◽

Anomalous Hall Effect ◽

Nodal Line ◽

Berry Curvature ◽

Curvature Driven

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Ultrafast non-excitonic valley Hall effect in MoS2/WTe2 heterobilayers

Nature Communications ◽

10.1038/s41467-021-21013-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jekwan Lee ◽

Wonhyeok Heo ◽

Myungjun Cha ◽

Kenji Watanabe ◽

Takashi Taniguchi ◽

...

Keyword(s):

Hall Effect ◽

Quantitative Information ◽

Exciton Energy ◽

Electron Hole ◽

Kerr Rotation ◽

Polarized Electrons ◽

Spatially Resolved ◽

Long Valley ◽

Bound Electron ◽

Valley Hall Effect

AbstractThe valley Hall effect (VHE) in two-dimensional (2D) van der Waals (vdW) crystals is a promising approach to study the valley pseudospin. Most experiments so far have used bound electron-hole pairs (excitons) through local photoexcitation. However, the valley depolarization of such excitons is fast, so that several challenges remain to be resolved. We address this issue by exploiting a unipolar VHE using a heterobilayer made of monolayer MoS2/WTe2 to exhibit a long valley-polarized lifetime due to the absence of electron-hole exchange interaction. The unipolar VHE is manifested by reduced photoluminescence at the MoS2 A exciton energy. Furthermore, we provide quantitative information on the time-dependent valley Hall dynamics by performing the spatially-resolved ultrafast Kerr-rotation microscopy; we find that the valley-polarized electrons persist for more than 4 nanoseconds and the valley Hall mobility exceeds 4.49 × 103 cm2/Vs, which is orders of magnitude larger than previous reports.

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