Tunable Orbital Ferromagnetism at Noninteger Filling of a Moiré Superlattice

Guorui Chen; Aaron L Sharpe; Eli J Fox; Shaoxin Wang; Bosai Lyu; Lili Jiang; Hongyuan Li; Kenji Watanabe; Takashi Taniguchi; Michael F Crommie; Marc A Kastner; Zhiwen Shi; David Goldhaber-Gordon; Yuanbo Zhang; Feng Wang

doi:10.1021/acs.nanolett.1c03699

Tunable Orbital Ferromagnetism at Noninteger Filling of a Moiré Superlattice

Nano Lett. 2022 Jan 12;22(1):238-245. doi: 10.1021/acs.nanolett.1c03699. Epub 2022 Jan 3.

Authors

Guorui Chen^{1

2}, Aaron L Sharpe^{3

4

5}, Eli J Fox^{3

6}, Shaoxin Wang¹, Bosai Lyu², Lili Jiang¹, Hongyuan Li^{1

7}, Kenji Watanabe⁸, Takashi Taniguchi⁹, Michael F Crommie^{1

7

10}, Marc A Kastner^{3

4

11}, Zhiwen Shi², David Goldhaber-Gordon^{3

4}, Yuanbo Zhang^{12

13}, Feng Wang^{1

7

10}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States.
² Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
³ Department of Applied Physics, Stanford University, Stanford, California 94305, United States.
⁴ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
⁵ Quantum and Electronic Materials Department, Sandia National Laboratories, Livermore, California 94550, United States.
⁶ Department of Physics, Stanford University, Stanford, California 94305, United States.
⁷ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
⁸ Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
⁹ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
¹⁰ Kavli Energy NanoSciences Institute, University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
¹¹ Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
¹² State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
¹³ Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China.

PMID: 34978444
DOI: 10.1021/acs.nanolett.1c03699

Abstract

The flat bands resulting from moiré superlattices exhibit fascinating correlated electron phenomena such as correlated insulators, ( Nature 2018, 556 (7699), 80-84), ( Nature Physics 2019, 15 (3), 237) superconductivity, ( Nature 2018, 556 (7699), 43-50), ( Nature 2019, 572 (7768), 215-219) and orbital magnetism. ( Science 2019, 365 (6453), 605-608), ( Nature 2020, 579 (7797), 56-61), ( Science 2020, 367 (6480), 900-903) Such magnetism has been observed only at particular integer multiples of n₀, the density corresponding to one electron per moiré superlattice unit cell. Here, we report the experimental observation of ferromagnetism at noninteger filling (NIF) of a flat Chern band in a ABC-TLG/hBN moiré superlattice. This state exhibits prominent ferromagnetic hysteresis behavior with large anomalous Hall resistivity in a broad region of densities centered in the valence miniband at n = -2.3n₀. We observe that, not only the magnitude of the anomalous Hall signal, but also the sign of the hysteretic ferromagnetic response can be modulated by tuning the carrier density and displacement field. Rotating the sample in a fixed magnetic field demonstrates that the ferromagnetism is highly anisotropic and likely purely orbital in character.

Keywords: anomalous Hall effect; electronic correlations; moiré superlattice; orbital magnetism; trilayer graphene.