Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers

Mak, Kin Fai; Tao, Zui; Shen, Bowen; Jiang, Shengwei; Li, Tingxin; Li, Lizhong; Ma, Liguo; Zhao, Wenjin; Hu, Jenny; Pistunova, Kateryna; Watanabe, Kenji; Taniguchi, Takashi; Heinz, Tony F.; Shan, Jie

doi:10.21203/rs.3.rs-2015885/v1

“…3 for images at intermediate temperatures). This is consistent with the reported ferromagnetic ordering temperature K of the Chern insulator state 31,32 . However, when the device is biased at 3.3 µA along the long axis, we observe MCD of opposite signs on two edges of the channel and zero MCD in the middle of the channel.…”

Section: The Spin Hall Effectsupporting

confidence: 92%

“…electron-electron interactions can further induce ferromagnetic instability and a Chern insulator 31 with spin degeneracy spontaneously lifted in each TMD layer 32 . In addition, long spin relaxation time (> 8 µs) near , presumably also from the strong electron-electron interactions, has been observed in related TMD moiré bilayers 33 (independent of the Chern state).…”

mentioning

confidence: 99%

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Tao,

Shen,

Zhao

et al. 2023

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The spin Hall effect (SHE), in which electrical current generates transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons [1][2][3][4][5][6][7] . The phenomenon originates from spin-orbit coupling. In general, stronger spin-orbit coupling favors larger SHEs but shorter spin relaxation times and diffusion lengths 1,4-7 . To achieve both large SHEs and longrange spin transport in a single material has remained a challenge. Here we demonstrate a giant intrinsic SHE in AB-stacked MoTe 2 /WSe 2 moiré bilayers by direct magneto optical imaging. Under moderate electrical currents with density < 1 A/m, we observe spin accumulation on transverse sample edges that nearly saturates the spin density. We also demonstrate long-range spin Hall transport and e cient nonlocal spin accumulation limited only by the device size (about 10 µm). The gate dependence shows that the giant SHE occurs only near the Chern insulating state, and at low temperatures, it emerges after the quantum anomalous Hall breakdown. Our results demonstrate moiré engineering of Berry curvature and large SHEs for potential spintronics applications. MainThe spin Hall effect has two distinct mechanisms, intrinsic and extrinsic, in a material 7 . The intrinsic effect is caused by spin-orbit coupling in the material's electronic band structure, whereas the extrinsic effect is caused by spin-orbit coupling between electrons and impurities through scattering. Materials with large intrinsic SHEs are sought after for spintronics applications [4][5][6][7] . The intrinsic spin Hall conductivity is directly related to the spin-dependent Berry curvature, which acts like a magnetic eld in momentum space. Particularly, monolayer transition metal dichalcogenides (TMDs) with strong Ising spin-orbit coupling exhibit opposite Berry curvature at the K and K' valleys, which is also spin dependent due to spin-momentum locking [8][9][10][11][12] . The non-zero Berry curvature has manifested a valley and spin Hall effect in doped monolayer TMD semiconductors 13,14 . But the effect is weak because Berry curvature spreads over large momentum space near the K (K') point in the case of large band gaps. Tailoring the electronic band structure by forming moiré heterostructures, speci cally creating gapped band crossings with small gaps near the Fermi level, opens a new route to generate Berry curvature hotspots and large SHEs [15][16][17][18][19][20] .Moiré materials are a highly tunable electronic system, in which rich quantum phenomena from the effects of strong electronic correlations and nontrivial band topology have been realized [16][17][18][19][20] . One such example is AB-stacked (60-degree-aligned) MoTe 2 /WSe 2 moiré bilayers. The TMD bilayers form a triangular moiré lattice. But the Wannier orbitals of the topmost MoTe 2 and WSe 2 moiré valence states are centered at two different sublattice sites and form an effective honeycomb lattice [21][22][23] . The lowenergy physics can be mapped to the Kane-Mele m...

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“…The first carriers added to the system go into the MoTe 2 layer, forming a correlated metal, which at n = 1 becomes a triangularlattice Mott insulator with 120 ∘ antiferromagnetic (AFM) order. At carrier concentration n = 1, decreasing Δ is predicted (14)(15)(16)(17)(18)27) and observed (1,2) to cause a transition to a quantum anomalous Hall (QAH) state, followed by a transition to a conventional metallic state. At Δ > 0, carriers in excess of the Mott concentration at half-filling (n = 1 per moiré unit cell) go into the WSe 2 band (if, as we assume, U > Δ) and are coupled to the spins of the Mott insulator via an exchange coupling J K ≏ t 2 h =Δ derived perturbatively from the interlayer hybridization t h so that the MoTe 2 /WSe 2 system can be described by an effective Kondo lattice model on the moiré scale whose study is the central topic of this paper.…”

Section: Introductionmentioning

confidence: 99%

Chiral Kondo lattice in doped MoTe ₂ /WSe ₂ bilayers

Guerci

¹

,

Wang

²

,

Zang

³

et al. 2023

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We theoretically study the interplay between magnetism and a heavy Fermi liquid in the AB-stacked transition metal dichalcogenide bilayer system, MoTe 2 /WSe 2 , in the regime in which the Mo layer supports localized magnetic moments coupled by interlayer electron tunneling to a weakly correlated band of itinerant electrons in the W layer. We show that the interlayer electron transfer leads to a chiral Kondo exchange, with consequences including a strong dependence of the Kondo temperature on carrier concentration and anomalous Hall effect due to a topological hybridization gap. The theoretical model exhibits two phases, a small Fermi surface magnet and a large Fermi surface heavy Fermi liquid; at the mean-field level, the transition between them is first order. Our results provide concrete experimental predictions for ongoing experiments on MoTe 2 /WSe 2 bilayer heterostructures and introduces a controlled route to observe a topological selective Mott transition.

show abstract

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Tao

¹

,

Shen

²

,

Zhao

³

et al. 2023

Preprint

Self Cite

5

0

View full text Add to dashboard Cite

The spin Hall effect (SHE), in which electrical current generates transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons 1–7. The phenomenon originates from spin-orbit coupling. In general, stronger spin-orbit coupling favors larger SHEs but shorter spin relaxation times and diffusion lengths 1,4–7. To achieve both large SHEs and long-range spin transport in a single material has remained a challenge. Here we demonstrate a giant intrinsic SHE in AB-stacked MoTe2/WSe2 moiré bilayers by direct magneto optical imaging. Under moderate electrical currents with density < 1 A/m, we observe spin accumulation on transverse sample edges that nearly saturates the spin density. We also demonstrate long-range spin Hall transport and efficient non-local spin accumulation limited only by the device size (about 10 µm). The gate dependence shows that the giant SHE occurs only near the Chern insulating state, and at low temperatures, it emerges after the quantum anomalous Hall breakdown. Our results demonstrate moiré engineering of Berry curvature and large SHEs for potential spintronics applications.

show abstract

Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers

Cited by 3 publications

References 34 publications

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Chiral Kondo lattice in doped MoTe ₂ /WSe ₂ bilayers

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

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Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers

Cited by 3 publications

References 34 publications

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

Chiral Kondo lattice in doped MoTe 2 /WSe 2 bilayers

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

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Chiral Kondo lattice in doped MoTe ₂ /WSe ₂ bilayers