Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice

Guorui Chen, Aaron L. Sharpe, Eli J. Fox, Ya-Hui Zhang, Shaoxin Wang, Lili Jiang, Bosai Lyu, Hongyuan Li, Kenji Watanabe, Takashi Taniguchi, Zhiwen Shi, T. Senthil, David Goldhaber-Gordon (), Yuanbo Zhang () and Feng Wang ()
Additional contact information
Guorui Chen: Lawrence Berkeley National Laboratory
Aaron L. Sharpe: Stanford University
Eli J. Fox: SLAC National Accelerator Laboratory
Ya-Hui Zhang: Massachusetts Institute of Technology
Shaoxin Wang: University of California at Berkeley
Lili Jiang: University of California at Berkeley
Bosai Lyu: Shanghai Jiao Tong University
Hongyuan Li: Lawrence Berkeley National Laboratory
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Zhiwen Shi: Shanghai Jiao Tong University
T. Senthil: Massachusetts Institute of Technology
David Goldhaber-Gordon: SLAC National Accelerator Laboratory
Yuanbo Zhang: Collaborative Innovation Center of Advanced Microstructures
Feng Wang: Lawrence Berkeley National Laboratory

Nature, 2020, vol. 579, issue 7797, 56-61

Abstract: Abstract Studies of two-dimensional electron systems in a strong magnetic field revealed the quantum Hall effect1, a topological state of matter featuring a finite Chern number C and chiral edge states2,3. Haldane4 later theorized that Chern insulators with integer quantum Hall effects could appear in lattice models with complex hopping parameters even at zero magnetic field. The ABC-trilayer graphene/hexagonal boron nitride (ABC-TLG/hBN) moiré superlattice provides an attractive platform with which to explore Chern insulators because it features nearly flat moiré minibands with a valley-dependent, electrically tunable Chern number5,6. Here we report the experimental observation of a correlated Chern insulator in an ABC-TLG/hBN moiré superlattice. We show that reversing the direction of the applied vertical electric field switches the moiré minibands of ABC-TLG/hBN between zero and finite Chern numbers, as revealed by large changes in magneto-transport behaviour. For topological hole minibands tuned to have a finite Chern number, we focus on quarter filling, corresponding to one hole per moiré unit cell. The Hall resistance is well quantized at h/2e2 (where h is Planck’s constant and e is the charge on the electron), which implies C = 2, for a magnetic field exceeding 0.4 tesla. The correlated Chern insulator is ferromagnetic, exhibiting substantial magnetic hysteresis and a large anomalous Hall signal at zero magnetic field. Our discovery of a C = 2 Chern insulator at zero magnetic field should open up opportunities for discovering correlated topological states, possibly with topological excitations7, in nearly flat and topologically nontrivial moiré minibands.

Date: 2020
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DOI: 10.1038/s41586-020-2049-7

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