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; Feng Wang

doi:10.1038/s41586-020-2049-7

Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice

Nature. 2020 Mar;579(7797):56-61. doi: 10.1038/s41586-020-2049-7. Epub 2020 Mar 4.

Authors

Guorui Chen^{1

2}, Aaron L Sharpe^{3

4}, Eli J Fox^{4

5}, Ya-Hui Zhang⁶, Shaoxin Wang², Lili Jiang², Bosai Lyu^{7

8}, Hongyuan Li^{1

2}, Kenji Watanabe⁹, Takashi Taniguchi⁹, Zhiwen Shi^{7

8}, T Senthil⁶, David Goldhaber-Gordon^{10

11}, Yuanbo Zhang^{12

13

14}, Feng Wang^{15

16

17}

Affiliations

¹ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
² Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
³ Department of Applied Physics, Stanford University, Stanford, CA, USA.
⁴ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁵ Department of Physics, Stanford University, Stanford, CA, USA.
⁶ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁷ Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China.
⁸ Collaborative Innovation Center of Advanced Microstructures, Nanjing, China.
⁹ National Institute for Materials Science, Tsukuba, Japan.
¹⁰ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA. [email protected].
¹¹ Department of Physics, Stanford University, Stanford, CA, USA. [email protected].
¹² Collaborative Innovation Center of Advanced Microstructures, Nanjing, China. [email protected].
¹³ State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China. [email protected].
¹⁴ Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China. [email protected].
¹⁵ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁶ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹⁷ Kavli Energy NanoSciences Institute at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].

PMID: 32132694
DOI: 10.1038/s41586-020-2049-7

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 states^2,3. 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 number^5,6. 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.