scholarly journals Quantum Valley Hall Effect, Orbital Magnetism, and Anomalous Hall Effect in Twisted Multilayer Graphene Systems

2019 ◽  
Vol 9 (3) ◽  
Author(s):  
Jianpeng Liu ◽  
Zhen Ma ◽  
Jinhua Gao ◽  
Xi Dai
Keyword(s):  
Hall Effect ◽  
Anomalous Hall Effect ◽  
Multilayer Graphene ◽  
Orbital Magnetism ◽  
Valley Hall Effect

scholarly journals Spin-polarized Dirac cone, flat band and saddle point in kagome magnet YMn6Sn6

2020 ◽  
Author(s):  
Man Li ◽  
Qi Wang ◽  
Guangwei Wang ◽  
Zhihong Yuan ◽  
Wenhua Song ◽  
...  
Keyword(s):  
Saddle Point ◽  
Hall Effect ◽  
Anomalous Hall Effect ◽  
Flat Band ◽  
Dirac Fermion ◽  
Kagome Lattice ◽  
Dirac Cone ◽  
Kagomé Lattice ◽  
Orbital Magnetism ◽  
Spin Polarized

Abstract Kagome-lattice of 3d-transition metals hosting Weyl/Dirac fermions and topological flat bands exhibit non-trivial topological characters and novel quantum phases, such as anomalous Hall effect and fractional quantum Hall effect. With consideration of spin-orbit coupling and electron correlation, several instabilities could be induced. The complete characters of the electronic structure of kagome lattice, i.e. the saddle point, Dirac-cone, and flat band, around the Fermi energy (EF) remain elusive in magnetic kagome materials. We present the first experimental observation of the complete features in ferromagnetic kagome layers of YMn6Sn6 helically coupled along the c-axis, by using angle-resolved photoemission spectroscopy and band structure calculations. We demonstrate a Dirac dispersion near EF arising from a spin-polarized orbital, which carries an intrinsic Berry curvature and contributes to the anomalous Hall effect in transport measurements. In addition, a flat band and a saddle point with a high density of states and with orbital-selective characters near EF are observed. These multi-orbital kagome features could cause multi-orbital magnetism. The Dirac fermion, flat band and saddle point in the vicinity of EF open an opportunity in manipulating the topological properties in magnetic materials.

Anomalous Hall effect in SmN: Influence of orbital magnetism and 4f -band conduction

2018 ◽  
Vol 98 (23) ◽  
Author(s):  
W. F. Holmes-Hewett ◽  
F. H. Ullstad ◽  
B. J. Ruck ◽  
F. Natali ◽  
H. J. Trodahl
Keyword(s):  
Hall Effect ◽  
Anomalous Hall Effect ◽  
Orbital Magnetism ◽  
Band Conduction

scholarly journals Bulk valley transport and Berry curvature spreading at the edge of flat bands

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Subhajit Sinha ◽  
Pratap Chandra Adak ◽  
R. S. Surya Kanthi ◽  
Bheema Lingam Chittari ◽  
L. D. Varma Sangani ◽  
...  
Keyword(s):  
Hall Effect ◽  
Recent Observation ◽  
High Sensitivity ◽  
Anomalous Hall Effect ◽  
Bilayer Graphene ◽  
Flat Band ◽  
Berry Curvature ◽  
Flat Bands ◽  
Current Path ◽  
Orbital Magnetism

Abstract 2D materials based superlattices have emerged as a promising platform to modulate band structure and its symmetries. In particular, moiré periodicity in twisted graphene systems produces flat Chern bands. The recent observation of anomalous Hall effect (AHE) and orbital magnetism in twisted bilayer graphene has been associated with spontaneous symmetry breaking of such Chern bands. However, the valley Hall state as a precursor of AHE state, when time-reversal symmetry is still protected, has not been observed. Our work probes this precursor state using the valley Hall effect. We show that broken inversion symmetry in twisted double bilayer graphene (TDBG) facilitates the generation of bulk valley current by reporting experimental evidence of nonlocal transport in a nearly flat band system. Despite the spread of Berry curvature hotspots and reduced quasiparticle velocities of the carriers in these flat bands, we observe large nonlocal voltage several micrometers away from the charge current path — this persists when the Fermi energy lies inside a gap with large Berry curvature. The high sensitivity of the nonlocal voltage to gate tunable carrier density and gap modulating perpendicular electric field makes TDBG an attractive platform for valley-twistronics based on flat bands.

scholarly journals Dirac cone, flat band and saddle point in kagome magnet YMn6Sn6

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Man Li ◽  
Qi Wang ◽  
Guangwei Wang ◽  
Zhihong Yuan ◽  
Wenhua Song ◽  
...  
Keyword(s):  
Saddle Point ◽  
Hall Effect ◽  
Theoretical Calculations ◽  
Anomalous Hall Effect ◽  
Flat Band ◽  
Dirac Fermion ◽  
Dirac Fermions ◽  
Dirac Cone ◽  
Fractional Quantum Hall ◽  
Orbital Magnetism

AbstractKagome-lattices of 3d-transition metals hosting Weyl/Dirac fermions and topological flat bands exhibit non-trivial topological characters and novel quantum phases, such as the anomalous Hall effect and fractional quantum Hall effect. With consideration of spin–orbit coupling and electron correlation, several instabilities could be induced. The typical characters of the electronic structure of a kagome lattice, i.e., the saddle point, Dirac-cone, and flat band, around the Fermi energy (EF) remain elusive in magnetic kagome materials. We present the experimental observation of the complete features in ferromagnetic kagome layers of YMn6Sn6 helically coupled along the c-axis, by using angle-resolved photoemission spectroscopy and band structure calculations. We demonstrate a Dirac dispersion near EF, which is predicted by spin-polarized theoretical calculations, carries an intrinsic Berry curvature and contributes to the anomalous Hall effect in transport measurements. In addition, a flat band and a saddle point with a high density of states near EF are observed. These multi-sets of kagome features are of orbital-selective origin and could cause multi-orbital magnetism. The Dirac fermion, flat band and saddle point in the vicinity of EF open an opportunity in manipulating the topological properties in magnetic materials.

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

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

scholarly journals Anomalous Hall effect in a magnetically extended topological insulator heterostructure

2020 ◽  
Vol 4 (9) ◽  
Author(s):  
Nan Liu ◽  
Xuefan Niu ◽  
Yuxin Liu ◽  
Qinghua Zhang ◽  
Lin Gu ◽  
...  
Keyword(s):  
Hall Effect ◽  
Topological Insulator ◽  
Anomalous Hall Effect

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

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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