Isospin competitions and valley polarized correlated insulators in twisted double bilayer graphene

Liu, Le; Zhang, Shihao; Chu, Yanbang; Shen, Cheng; Huang, Yuan; Yuan, Yalong; Tian, Jinpeng; Tang, Jian; Ji, Yiru; Yang, Rong; Watanabe, Kenji; Taniguchi, Takashi; Shi, Dongxia; Liu, Jianpeng; Yang, Wei; Zhang, Guangyu

doi:10.1038/s41467-022-30998-x

Cited by 30 publications

(26 citation statements)

References 44 publications

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“…往往存在着自旋极化的向列序态, 并且垂直磁场可以诱发这类体系从自旋极化向列序态到谷极化陈绝缘体态的拓扑相变 [83,84] . 而针对转角双层石墨烯中声子性质的深度学习分子动力学研究, 发现了若干极低频率的面外"弯曲"声子模式, 并且这些极低频模式与电子耦合可能导致关联绝缘态以及电四极矩序 [85] .…”

Section: 而在各类转角多层石墨烯体系中平带在半填充时unclassified

“…这跟之前的理论结果是一致的 [163] . Zhang等 [83] 通过分石墨烯等体系中, 都是广泛存在的 [83] . 图6(b)给出了转角双层-双层石墨烯在位移电场下的电荷分布图, 呈现出条纹状图案, 符合近期扫描隧道显微镜的观测结果 [70] .…”

Section: 转角多层石墨烯体系中的自旋向列序态unclassified

“…下面重点分析这些莫尔尺度上的面外"弯曲"声子模式 [85] . (b)转角双层-双层石墨烯半填充处的实空间电荷分布 [83] ; (c)-(e)转角双层-单层石墨烯体系在不同Hubbard参数和磁场下衍生出的不同陈数的绝缘态, 用红线标记 [83] Fig. 6.…”

Section: 因此垂直磁场往往驱动着体系变成破缺时间反演unclassified

“…"SP" and "VP" stand for "spin polarized" and "valley polarized" respectively; (b) charge density distribution in real space at half filling for twisted double bilayer graphene [83] ; (c)-(e) calculated gapped states with different Chern numbers remarked by red lines under magnetic fields in the twisted bilayer-monolayer graphene system [83] .…”

Section: 因此垂直磁场往往驱动着体系变成破缺时间反演mentioning

confidence: 99%

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Novel electrical properties of moiré graphene systems

Zhang¹,

Xie²,

Peng³

et al. 2023

Acta Phys. Sin.

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In this review, we discuss the electronic structures, topological properties, correlated states, nonlinear optical responses, as well as phonon and electron-phonon coupling effects of moiré graphene superlattices. First, we illustrate that topologically non-trivial flat bands and moiré orbital magnetism are ubiquitous in various twisted graphene systems. In particular, the topological flat bands of magic-angle twisted bilayer graphene (TBG) can be explained from a zeroth pseudo-Landau-level picture, which can naturally explain the experimentally observed quantum anomalous Hall effect and some of the other correlated states. These topologically nontrivial flat bands may lead to nearly quantized piezoelectric response, which can be used to directly probe the valley Chern numbers in these moiré graphene systems. A simple and general chiral decomposition rule is reviewed and discussed, which can be used to predict the low-energy band dispersions of generic twisted mulilayer graphene system and alternating twisted multilayer graphene system. This review further discusses nontrivial interaction effects of magic-angle TBG such as the correlated insulator states, density wave states, cascade transitions, and nematic states, and proposes nonlinear optical measurement as an experimental probe to distinguish the different "featureless" correlated states.The phonon properties and electron-phonon coupling effects are also briefly reviewed. The novel physics emerging from band-aligned graphene-insulator heterostructres is also discussed in this review. In the end, we make a summary and an outlook about the novel physical properties of moiré superlattices, two-dimensional materials, moiré superlattices－ two dimensional materials.

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Section: 而在各类转角多层石墨烯体系中平带在半填充时unclassified

Section: 转角多层石墨烯体系中的自旋向列序态unclassified

Section: 因此垂直磁场往往驱动着体系变成破缺时间反演unclassified

Section: 因此垂直磁场往往驱动着体系变成破缺时间反演mentioning

confidence: 99%

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Novel electrical properties of moiré graphene systems

Zhang¹,

Xie²,

Peng³

et al. 2023

Acta Phys. Sin.

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“…Notably, the flat bands in TDBG possess a nonzero valley Chern number that changes with the electric field, offering a unique correlated Hofstadter platform 27 . While earlier experiments in TDBG have a major focus on electron correlations physics 28 – 34 , the tunability of the topological flat bands in the Hofstadter regime is little explored 35 . An ability to tune the Chern numbers of these bands would provide further insight on the role of topology in these correlated states.…”

Section: Introductionmentioning

confidence: 99%

Perpendicular electric field drives Chern transitions and layer polarization changes in Hofstadter bands

et al. 2022

Self Cite

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Moiré superlattices engineer band properties and enable observation of fractal energy spectra of Hofstadter butterfly. Recently, correlated-electron physics hosted by flat bands in small-angle moiré systems has been at the foreground. However, the implications of moiré band topology within the single-particle framework are little explored experimentally. An outstanding problem is understanding the effect of band topology on Hofstadter physics, which does not require electron correlations. Our work experimentally studies Chern state switching in the Hofstadter regime using twisted double bilayer graphene (TDBG), which offers electric field tunable topological bands, unlike twisted bilayer graphene. Here we show that the nontrivial topology reflects in the Hofstadter spectra, in particular, by displaying a cascade of Hofstadter gaps that switch their Chern numbers sequentially while varying the perpendicular electric field. Our experiments together with theoretical calculations suggest a crucial role of charge polarization changing concomitantly with topological transitions in this system. Layer polarization is likely to play an important role in the topological states in few-layer twisted systems. Moreover, our work establishes TDBG as a novel Hofstadter platform with nontrivial magnetoelectric coupling.

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Enhancing 2D Photonics and Optoelectronics with Artificial Microstructures

Song,

Chen,

Sun

et al. 2024

Advanced Science

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By modulating subwavelength structures and integrating functional materials, 2D artificial microstructures (2D AMs), including heterostructures, superlattices, metasurfaces and microcavities, offer a powerful platform for significant manipulation of light fields and functions. These structures hold great promise in high‐performance and highly integrated optoelectronic devices. However, a comprehensive summary of 2D AMs remains elusive for photonics and optoelectronics. This review focuses on the latest breakthroughs in 2D AM devices, categorized into electronic devices, photonic devices, and optoelectronic devices. The control of electronic and optical properties through tuning twisted angles is discussed. Some typical strategies that enhance light‐matter interactions are introduced, covering the integration of 2D materials with external photonic structures and intrinsic polaritonic resonances. Additionally, the influences of external stimuli, such as vertical electric fields, enhanced optical fields and plasmonic confinements, on optoelectronic properties is analysed. The integrations of these devices are also thoroughly addressed. Challenges and future perspectives are summarized to stimulate research and development of 2D AMs for future photonics and optoelectronics.

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Isospin competitions and valley polarized correlated insulators in twisted double bilayer graphene

Cited by 30 publications

References 44 publications

Novel electrical properties of moiré graphene systems

Novel electrical properties of moiré graphene systems

Perpendicular electric field drives Chern transitions and layer polarization changes in Hofstadter bands

Enhancing 2D Photonics and Optoelectronics with Artificial Microstructures

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