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Melchakova IA, Oyeniyi GT, Polyutov SP, Avramov PV. Spin Polarization and Flat Bands in Eu-Doped Nanoporous and Twisted Bilayer Graphenes. MICROMACHINES 2023; 14:1889. [PMID: 37893326 PMCID: PMC10609095 DOI: 10.3390/mi14101889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Revised: 09/25/2023] [Accepted: 09/28/2023] [Indexed: 10/29/2023]
Abstract
Advanced two-dimensional spin-polarized heterostructures based on twisted (TBG) and nanoporous (NPBG) bilayer graphenes doped with Eu ions were theoretically proposed and studied using Periodic Boundary Conditions Density Functional theory electronic structure calculations. The significant polarization of the electronic states at the Fermi level was discovered for both Eu/NPBG(AA) and Eu/TBG lattices. Eu ions' chemi- and physisorption to both graphenes may lead to structural deformations, drop of symmetry of low-dimensional lattices, interlayer fusion, and mutual slides of TBG graphene fragments. The frontier bands in the valence region at the vicinity of the Fermi level of both spin-polarized 2D Eu/NPBG(AA) and Eu/TBG lattices clearly demonstrate flat dispersion laws caused by localized electronic states formed by TBG Moiré patterns, which could lead to strong electron correlations and the formation of exotic quantum phases.
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Affiliation(s)
- Iu. A. Melchakova
- School of Physics and Engineering, ITMO University, 197101 St. Petersburg, Russia;
| | - G. T. Oyeniyi
- Department of Chemistry, Kyungpook National University, Daegu 41566, Republic of Korea;
| | - S. P. Polyutov
- International Research Center of Spectroscopy and Quantum Chemistry (IRC SQC), Siberian Federal University, Svobodniy pr. 79/10, 600041 Krasnoyarsk, Russia;
| | - P. V. Avramov
- Department of Chemistry, Kyungpook National University, Daegu 41566, Republic of Korea;
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Spontaneous time-reversal symmetry breaking in twisted double bilayer graphene. Nat Commun 2022; 13:6468. [PMID: 36309518 PMCID: PMC9617879 DOI: 10.1038/s41467-022-34192-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 10/12/2022] [Indexed: 11/08/2022] Open
Abstract
Twisted double bilayer graphene (tDBG) comprises two Bernal-stacked bilayer graphene sheets with a twist between them. Gate voltages applied to top and back gates of a tDBG device tune both the flatness and topology of the electronic bands, enabling an unusual level of experimental control. Metallic states with broken spin and valley symmetries have been observed in tDBG devices with twist angles in the range 1.2–1.3°, but the topologies and order parameters of these states have remained unclear. We report the observation of an anomalous Hall effect in the correlated metal state of tDBG, with hysteresis loops spanning hundreds of mT in out-of-plane magnetic field (B⊥) that demonstrate spontaneously broken time-reversal symmetry. The B⊥ hysteresis persists for in-plane fields up to several Tesla, suggesting valley (orbital) ferromagnetism. At the same time, the resistivity is strongly affected by even mT-scale values of in-plane magnetic field, pointing to spin-valley coupling or to a direct orbital coupling between in-plane field and the valley degree of freedom. Twisted double bilayer graphene (tDBG) comprises two Bernal-stacked bilayer graphene sheets with a twist between them. Here, the authors report a strong anomalous Hall effect in the correlated-metal regime of tDBG, indicating time reversal symmetry breaking from orbital ferromagnetism, likely associated with valley polarization.
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Lin JX, Zhang YH, Morissette E, Wang Z, Liu S, Rhodes D, Watanabe K, Taniguchi T, Hone J, Li JIA. Spin-orbit-driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene. Science 2022; 375:437-441. [PMID: 34990215 DOI: 10.1126/science.abh2889] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Strong electron correlation and spin-orbit coupling (SOC) can have a profound influence on the electronic properties of materials. We examined their combined influence on a two-dimensional electronic system at the atomic interface between magic-angle twisted bilayer graphene and a tungsten diselenide crystal. We found that strong electron correlation within the moiré flatband stabilizes correlated insulating states at both quarter and half filling, and that SOC transforms these Mott-like insulators into ferromagnets, as evidenced by a robust anomalous Hall effect with hysteretic switching behavior. The coupling between spin and valley degrees of freedom could be demonstrated through control of the magnetic order with an in-plane magnetic field or a perpendicular electric field. Our findings establish an experimental knob to engineer topological properties of moiré bands in twisted bilayer graphene and related systems.
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Affiliation(s)
- Jiang-Xiazi Lin
- Department of Physics, Brown University, Providence, RI 02912, USA
| | - Ya-Hui Zhang
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - Erin Morissette
- Department of Physics, Brown University, Providence, RI 02912, USA
| | - Zhi Wang
- Department of Physics, Brown University, Providence, RI 02912, USA
| | - Song Liu
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Daniel Rhodes
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - J I A Li
- Department of Physics, Brown University, Providence, RI 02912, USA
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Chen G, Sharpe AL, Fox EJ, Wang S, Lyu B, Jiang L, Li H, Watanabe K, Taniguchi T, Crommie MF, Kastner MA, Shi Z, Goldhaber-Gordon D, Zhang Y, Wang F. Tunable Orbital Ferromagnetism at Noninteger Filling of a Moiré Superlattice. NANO LETTERS 2022; 22:238-245. [PMID: 34978444 DOI: 10.1021/acs.nanolett.1c03699] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
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.
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Affiliation(s)
- Guorui Chen
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
- 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
| | - Aaron L Sharpe
- Department of Applied Physics, Stanford University, Stanford, California 94305, United States
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Quantum and Electronic Materials Department, Sandia National Laboratories, Livermore, California 94550, United States
| | - Eli J Fox
- Department of Applied Physics, Stanford University, Stanford, California 94305, United States
- Department of Physics, Stanford University, Stanford, California 94305, United States
| | - Shaoxin Wang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
| | - Bosai Lyu
- 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
| | - Lili Jiang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
| | - Hongyuan Li
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Michael F Crommie
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Kavli Energy NanoSciences Institute, University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Marc A Kastner
- Department of Applied Physics, Stanford University, Stanford, California 94305, United States
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Zhiwen Shi
- 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
| | - David Goldhaber-Gordon
- Department of Applied Physics, Stanford University, Stanford, California 94305, United States
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Yuanbo Zhang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
- Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China
| | - Feng Wang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Kavli Energy NanoSciences Institute, University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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