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Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice
Studies of two-dimensional electron systems in a strong magnetic field revealed the quantum Hall effect 1 , a topological state of matter featuring a finite Chern number C and chiral edge states 2 , 3 . Haldane 4 later theorized that Chern insulators with integer quantum Hall effects could appear in...
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Published in: | Nature (London) 2020-03, Vol.579 (7797), p.56-61 |
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Main Authors: | , , , , , , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Studies of two-dimensional electron systems in a strong magnetic field revealed the quantum Hall effect
1
, a topological state of matter featuring a finite Chern number
C
and chiral edge states
2
,
3
. Haldane
4
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
/2
e
2
(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 excitations
7
, in nearly flat and topologically nontrivial moiré minibands.
A topological Chern insulating state is reported to emerge from strong correlations in flat moiré bands in a graphene superlattice and by applying a vertical electric field the Chern number is switched. |
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ISSN: | 0028-0836 1476-4687 |
DOI: | 10.1038/s41586-020-2049-7 |