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Evidence of the fractional quantum spin Hall effect in moiré MoTe2

Cornell Affiliated Author(s)
Author
Kaifei Kang
Bowen Shen
Yichen Qiu
Yihang Zeng
Zhengchao Xia
Kenji Watanabe
Takashi Taniguchi
Jie Shan
Kin Mak
Abstract

Quantum spin Hall (QSH) insulators are two-dimensional electronic materials that have a bulk band gap like an ordinary insulator but have topologically protected pairs of edge modes of opposite chiralities. To date, experimental studies have found only integer QSH insulators with counter-propagating up-spins and down-spins at each edge leading to a quantized conductance G0=e^2/h. Here we report transport evidence of a fractional QSH insulator in 2.1-degree-twisted bilayer MoTe2, which supports spin-Sz conservation and flat spin-contrasting Chern bands.

Journal
Nature
Date Published
Funding Source
DE-SC0019481
FA9550-20-1-0219
DMR-1719875
GBMF11563
NNCI-2025233
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Observation of spin polarons in a frustrated moiré Hubbard system

Cornell Affiliated Author(s)
Author
Zui Tao
Wenjin Zhao
Bowen Shen
Tingxin Li
Patrick Knüppel
Kenji Watanabe
Takashi Taniguchi
Jie Shan
Kin Mak
Abstract

The electron’s kinetic energy plays a pivotal role in magnetism. While virtual electron hopping promotes antiferromagnetism in an insulator, real hopping processes usually favour ferromagnetism. However, in kinetically frustrated systems such as hole-doped triangular lattice Mott insulators, real hopping has instead been shown to favour antiferromagnetism. Kinetic frustration has also been predicted to induce a new quasiparticle, a bound state of the doped hole and a spin flip called a spin polaron, at intermediate magnetic fields, which could form an unusual metallic state.

Journal
Nature Physics
Date Published
Funding Source
FA9550-19-1-0390
DE-SC0019481
DMR-1807810
JPMJCR15F3
NNCI-2025233
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

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

Cornell Affiliated Author(s)
Author
Z. Tao
B. Shen
W. Zhao
N.C. Hu
T. Li
S. Jiang
L. Li
K. Watanabe
T. Taniguchi
A.H. MacDonald
J. Shan
K.F. Mak
Abstract

The spin Hall effect (SHE), in which an electrical current generates a transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons. The phenomenon originates from spin–orbit coupling. In general, stronger spin–orbit coupling favours larger SHEs but shorter spin relaxation times and diffusion lengths. However, correlated magnetic materials often do not support large SHEs.

Journal
Nature Nanotechnology
Date Published
Funding Source
DMR-1719875
DMR-1807810
DMR-2039380
FA9550-19-1-0390
NNCI-2025233
DE-SC0019481
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Remote imprinting of moiré lattices

Author
J. Gu
J. Zhu
P. Knuppel
K. Watanabe
T. Taniguchi
J. Shan
K.F. Mak
Abstract

Two-dimensional moiré materials are formed by overlaying two layered crystals with small differences in orientation or/and lattice constant, where their direct coupling generates moiré potentials. Moiré materials have emerged as a platform for the discovery of new physics and device concepts, but while moiré materials are highly tunable, once formed, moiré lattices cannot be easily altered. Here we demonstrate the electrostatic imprinting of moiré lattices onto a target monolayer semiconductor.

Journal
Nature Materials
Date Published
Funding Source
DMR-2114535
NNCI-2025233
FA9550-18-1-0480
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Valley-Coherent Quantum Anomalous Hall State in AB-Stacked MoTe2/ W S e2 Bilayers

Cornell Affiliated Author(s)
Author
Z. Tao
B. Shen
S. Jiang
T. Li
L. Li
L. Ma
W. Zhao
J. Hu
K. Pistunova
K. Watanabe
T. Taniguchi
T.F. Heinz
K.F. Mak
J. Shan
Abstract

Moiré materials provide fertile ground for the correlated and topological quantum phenomena. Among them, the quantum anomalous Hall (QAH) effect, in which the Hall resistance is quantized even under zero magnetic field, is a direct manifestation of the intrinsic topological properties of a material and an appealing attribute for low-power electronics applications. The QAH effect has been observed in both graphene and transition metal dichalcogenide (TMD) moiré materials. It is thought to arise from the interaction-driven valley polarization of the narrow moiré bands.

Journal
Physical Review X
Date Published
Funding Source
DMR-1807810
NNCI-2025233
FA9550-19-1-0390
GBMF11563
GBMF9462
DE-SC0019481
FWP-100459
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Realization of the Haldane Chern insulator in a moiré lattice

Author
W. Zhao
K. Kang
Y. Zhang
P. Knuppel
Z. Tao
L. Li
C.L. Tschirhart
E. Redekop
K. Watanabe
T. Taniguchi
A.F. Young
J. Shan
K.F. Mak
Abstract

The Chern insulator displays a quantized Hall effect without Landau levels. Theoretically, this state can be realized by engineering complex next-nearest-neighbour hopping in a honeycomb lattice—the so-called Haldane model. Despite its profound effect on the field of topological physics and recent implementation in cold-atom experiments, the Haldane model has not yet been realized in solid-state materials.

Journal
Nature Physics
Date Published
Funding Source
DMR-1807810
FA9550-19-1-0390
FA9550-20-1-0219
GBMF9471
W911NF-20-2-0166
DE-SC0019481
NNCI-2025233
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Switchable moiré potentials in ferroelectric WTe2/WSe2 superlattices

Cornell Affiliated Author(s)
Author
K. Kang
W. Zhao
Y. Zeng
K. Watanabe
T. Taniguchi
J. Shan
K.F. Mak
Abstract

Moiré materials with superlattice periodicity many times the atomic length scale have shown strong electronic correlations and band topology with unprecedented tunability. Non-volatile control of the moiré potentials could allow on-demand switching of superlattice effects but has remained challenging to achieve. Here we demonstrate the switching of the correlated and moiré band insulating states, and the associated nonlinear anomalous Hall effect, by the ferroelectric effect.

Journal
Nature Nanotechnology
Date Published
Funding Source
DMR-2039380
FA9550-18-1-0480
DE-SC0019481
DMR-1719875
NNCI-2025233
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Gate-tunable heavy fermions in a moiré Kondo lattice

Cornell Affiliated Author(s)
Author
W. Zhao
B. Shen
Z. Tao
Z. Han
K. Kang
K. Watanabe
T. Taniguchi
K.F. Mak
J. Shan
Abstract

The Kondo lattice—a matrix of local magnetic moments coupled through spin-exchange interactions to itinerant conduction electrons—is a prototype of strongly correlated quantum matter1–4. Usually, Kondo lattices are realized in intermetallic compounds containing lanthanide or actinide1,2. The complex electronic structure and limited tunability of both the electron density and exchange interactions in these bulk materials pose considerable challenges to studying Kondo lattice physics.

Journal
Nature
Date Published
Funding Source
DMR-2004451
DMR-2039380
NNCI-2025233
FA9550-19-1-0390
DE-SC0019481
DMR-1719875
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Intrinsic spin Hall torque in a moiré Chern magnet

Cornell Affiliated Author(s)
Author
C.L. Tschirhart
E. Redekop
L. Li
T. Li
S. Jiang
T. Arp
O. Sheekey
T. Taniguchi
K. Watanabe
M.E. Huber
K.F. Mak
J. Shan
A.F. Young
Abstract

In spin torque magnetic memories, electrically actuated spin currents are used to switch a magnetic bit. Typically, these require a multilayer geometry including both a free ferromagnetic layer and a second layer providing spin injection. For example, spin may be injected by a non-magnetic layer exhibiting a large spin Hall effect, a phenomenon known as spin–orbit torque. Here we demonstrate a spin–orbit torque magnetic bit in a single two-dimensional system with intrinsic magnetism and strong Berry curvature.

Journal
Nature Physics
Date Published
Funding Source
DMR-1906325
FA9550-19-1-0390
W911NF-20-2-0166
GBMF9471
1650114
19H05790
20H00354
21H05233
Group (Lab)
Jie Shan Group
Kin Fai Mak Group