Article
Multidisciplinary Sciences
Trithep Devakul, Patrick J. Ledwith, Li-Qiao Xia, Aviram Uri, Sergio C. de la Barrera, Pablo Jarillo-Herrero, Liang Fu
Summary: We propose magic-angle helical trilayer graphene (HTG) as a platform for realizing exotic correlated topological states of matter, and provide experimental evidence and theoretical explanations.
Article
Chemistry, Multidisciplinary
Hongzhen Zhong, Zhixin Su, Jun Kang
Summary: Recent studies have shown that 2D moire superlattices have the potential to be used as a quantum simulator for condensed matter systems. The interference between moire patterns at different interfaces in 2D multilayer structures allows the realization of more complex lattice models. In the specific case of trilayer moire superlattices (TMSLs) of MoS2, isolated flat moire bands near the valence band edge can be described by the honeycomb lattice ionic Hubbard model. The parameters in the TMSLs, such as the hopping strength, on-site Coulomb repulsion, and staggered potential, can be highly tunable through control of the twist angle, dielectric environment, and perpendicular electric field. This makes TMSLs a versatile platform for studying strong correlation physics in the honeycomb lattice ionic Hubbard model.
ADVANCED FUNCTIONAL MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Atasi Chakraborty, Kamal Das, Subhajit Sinha, Pratap Chandra Adak, Mandar M. Deshmukh, Amit Agarwal
Summary: Researchers investigated the family of second-order nonlinear anomalous (NLA) Hall effects in the moire system of twisted double bilayer graphene (TDBG), demonstrating that these effects can probe topological phase transitions. The study found that the entire family of NLA Hall responses undergo a sign reversal across a topological phase transition, establishing a deeper connection between valley topology and nonlinear Hall effects in time-reversal symmetric systems.
Article
Chemistry, Physical
Cheng Shen, Patrick J. Ledwith, Kenji Watanabe, Takashi Taniguchi, Eslam Khalaf, Ashvin Vishwanath, Dmitri K. Efetov
Summary: Magic-angle twisted trilayer graphene (MATTG) has flat electronic bands and exhibits correlated quantum phases. A spectroscopy technique is demonstrated in this work to dissociate intertwined bands and quantify the energy gaps and Chern numbers C of the correlated states in MATTG. Hard correlated gaps with C = 0 at integer moiré unit cell fillings and charge density wave states originating from van Hove singularities at fractional fillings are uncovered. Displacement-field-driven first-order phase transitions at charge neutrality and v = 2 are also demonstrated. Overall, these properties establish a diverse electrically tunable phase diagram of MATTG.
Article
Physics, Multidisciplinary
Junxi Duan, Yu Jian, Yang Gao, Huimin Peng, Jinrui Zhong, Qi Feng, Jinhai Mao, Yugui Yao
Summary: In the study, a giant second-order nonlinear Hall effect dominated by disorder-induced skew scattering was observed in twisted bilayer graphene. The magnitude and direction of the nonlinearity could be effectively tuned by gate voltage, and was mainly determined by the collaboration of static and dynamic disorders.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Yalong Yuan, Yanbang Chu, Cheng Hu, Jinpeng Tian, Le Liu, Fanfan Wu, Yiru Ji, Jiaojiao Zhao, Zhiheng Huang, Xiaozhou Zan, Luojun Du, Kenji Watanabe, Takashi Taniguchi, Dongxia Shi, Zhiwen Shi, Wei Yang, Guangyu Zhang
Summary: We demonstrate the epitaxial growth of trilayer graphene moire superlattice on hexagonal boron nitride using remote plasma-enhanced chemical vapor deposition. The resulting TLG/hBN exhibits a uniform moire pattern with a period of about 15 nm, showing strong electron-electron correlation and quantum Hall states. Our work suggests that epitaxy provides an easy and reproducible method for fabricating stable two-dimensional strongly correlated electronic materials.
Article
Materials Science, Multidisciplinary
Makoto Naka, Yukitoshi Motome, Hitoshi Seo
Summary: In this study, the anomalous Hall effect (AHE) in perovskites with antiferromagnetic (AFM) orderings was theoretically investigated. The results showed that AFM ordered states in perovskite materials can exhibit AHE, with different forms depending on the electron orbital filling.
Article
Chemistry, Multidisciplinary
Felix Winterer, Anna M. Seiler, Areg Ghazaryan, Fabian R. Geisenhof, Kenji Watanabe, Takashi Taniguchi, Maksym Serbyn, R. Thomas Weitz
Summary: In this study, the formation of Dirac gullies and the interaction-induced breakdown of gully coherence were explored through magnetotransport measurements in high-quality Bernal-stacked trilayer graphene. The emergence of Dirac gullies in the quantum Hall regime and the control of electron-electron interactions through electric and magnetic fields were observed, leading to the lifting of gully degeneracy and the formation of a correlated ground state.
Review
Physics, Applied
Jianpeng Liu, Xi Dai
Summary: The study of moire graphene systems has attracted considerable attention due to their exotic phenomena, which are closely related to valley-spin-degenerate and topologically non-trivial flat bands. Experimental evidence suggests that unconventional orbital magnetism is exhibited when time-reversal symmetry is broken spontaneously in these systems. Theoretical perspectives on the correlated insulating states and quantum anomalous Hall phenomena are discussed in this Perspective, emphasizing the topological nature of moire flat bands.
NATURE REVIEWS PHYSICS
(2021)
Article
Materials Science, Multidisciplinary
Fang Xie, Nicolas Regnault, Dumitru Calugaru, B. Andrei Bernevig, Biao Lian
Summary: The study uses Hartree-Fock mean field approach to investigate the Hamiltonian of magic-angle twisted symmetric trilayer graphene, revealing different phases at different fillings and offering insights into the electron interactions in the system.
Article
Chemistry, Multidisciplinary
Lixuan Tai, Bingqian Dai, Jie Li, Hanshen Huang, Su Kong Chong, Kin L. Wong, Huairuo Zhang, Peng Zhang, Peng Deng, Christopher Eckberg, Gang Qiu, Haoran He, Di Wu, Shijie Xu, Albert Davydov, Ruqian Wu, Kang L. Wang
Summary: In this study, the researchers confirm the genuine topological Hall effect (THE) with the anomalous Hall effect (AHE) through transport and magneto-optical Kerr effect microscopy. The presence of magnetic skyrmions is directly observed, and genuine THE is found to occur in the transition region of the AHE. The researchers also distinguish between artifact THE and genuine THE using minor loops, temperature dependence, and gate dependence.
Article
Physics, Multidisciplinary
Xianyan Han, Qianling Liu, Ruirui Niu, Zhuangzhuang Qu, Zhiyu Wang, Zhuoxian Li, Chunrui Han, Kenji Watanabe, Takashi Taniguchi, Zizhao Gan, Jianming Lu
Summary: This study investigates the symmetry-breaking transitions in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride using displacement fields and magnetic fields, revealing the mechanisms of various exotic phenomena in strongly correlated systems.
Article
Chemistry, Multidisciplinary
Aaron L. Sharpe, Eli J. Fox, Arthur W. Barnard, Joe Finney, Kenji Watanabe, Takashi Taniguchi, Marc A. Kastner, David Goldhaber-Gordon
Summary: This study demonstrates a highly anisotropic ferromagnetism in twisted bilayer graphene, which is associated with a Chern insulating state. The anisotropy is likely orbital in nature rather than spin-induced, and a transition to a new phase may occur when an in-plane magnetic field exceeds 5 T.
Article
Materials Science, Multidisciplinary
Valentin Crepel, Liang Fu
Summary: We predict strong Ising ferromagnetism driven by Coulomb interaction in the metallic phase of twisted transition metal dichalcogenide homobilayers for small twist angles. The spin-valley locking and Chern band result in a completely spin-polarized half metal with a spin gap and anomalous Hall effect. Near a magic angle with an exceptionally flat Chern band, the anomalous Hall metal at 1/3 filling may transition to a root 3 x root 3 charge density wave or a fractional Chern insulator.
Review
Chemistry, Multidisciplinary
Li Wang, Sisi Yin, Jianping Yang, Shi Xue Dou
Summary: 2D layered materials have been widely used as catalysts due to their unique properties. Moire superlattice structure in 2D materials plays a crucial role in modulating their electronic band structure and catalytic performance. However, the investigation of moire superlattice structure in catalytic applications is still in its early stages.
Article
Chemistry, Multidisciplinary
Dmitry Lebedev, Jonathan Tyler Gish, Ethan Skyler Garvey, Teodor Kosev Stanev, Junhwan Choi, Leonidas Georgopoulos, Thomas Wei Song, Hong Youl Park, Kenji Watanabe, Takashi Taniguchi, Nathaniel Patrick Stern, Vinod Kumar Sangwan, Mark Christopher Hersam
Summary: 2D magnetic materials have promising applications in quantum and spintronic devices. 2D antiferromagnetic materials are of interest due to their insensitivity to external magnetic fields and faster switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization hampers the detection and control of antiferromagnetic order, emphasizing the need for magneto-electrical measurements.
ADVANCED FUNCTIONAL MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Dohun Kim, Byungmin Kang, Yong-Bin Choi, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Lee, Gil Young Cho, Youngwook Kim
Summary: We introduce a novel two-dimensional electronic system called twisted bilayer graphene with a large twist angle, which exhibits ultrastrong interlayer interactions and is ideal for realizing interlayer-coherent excitonic condensates. By fully exploiting the sub-nanometer atomic separation and geometrically suppressed interlayer electron tunneling, we demonstrate the appearance of a sequence of odd-integer quantum Hall states with interlayer coherence at the second Landau level (N = 1). These states have energy gaps of order 1 K, several orders of magnitude greater than those in GaAs. Experimental observations of various quantum Hall phase transitions largely support our phenomenological model calculations. Therefore, we establish the excellent platform of a large twist angle system for high-temperature excitonic condensation.
Article
Nanoscience & Nanotechnology
Ryoichi Kato, Haruki Uchiyama, Tomonori Nishimura, Keiji Ueno, Takashi Taniguchi, Kenji Watanabe, Edward Chen, Kosuke Nagashio
Summary: In this study, high-performance p-type FETs were achieved by selectively applying surface charge-transfer doping from WOx to the access region of WS2 and WSe2. The p-type conversion of intrinsically n-type trilayer WSe2 FET was successfully achieved by reducing the Schottky barrier width and injecting holes into the valence band. However, trilayer WS2 did not show clear p-type conversion due to its lower valence band maximum compared to trilayer WSe2. Using h-BN as a TG insulator, a high-performance p-type WSe2 FET with negligible hysteresis was achieved.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Physics, Applied
Kento Sasaki, Yuki Nakamura, Hao Gu, Moeta Tsukamoto, Shu Nakaharai, Takuya Iwasaki, Kenji Watanabe, Takashi Taniguchi, Shinichi Ogawa, Yukinori Morita, Kensuke Kobayashi
Summary: Placing a sensor close to the target at the nano-level is a central challenge in quantum sensing. We demonstrate magnetic field imaging with a boron vacancy (V-B(-)) defects array in hexagonal boron nitride with a few 10 nm thickness. The sensor array allows us to visualize the magnetic field induced by the current in the straight micro wire with a high spatial resolution. Each sensor exhibits a practical sensitivity of 73.6 mu T/Hz(0.5), suitable for quantum materials research. Our technique of arranging V-B(-) quantum sensors periodically and tightly on measurement targets will maximize their potential.
APPLIED PHYSICS LETTERS
(2023)
Article
Chemistry, Multidisciplinary
Martin Endres, Artem Kononov, Hasitha Suriya Arachchige, Jiaqiang Yan, David Mandrus, Kenji Watanabe, Takashi Taniguchi, Christian Schoenenberger
Summary: In this study, we measured a 4N-periodic switching current through an asymmetric SQUID formed by the higher-order topological insulator WTe2. We found that a high asymmetry in critical current and negligible loop inductance alone were not sufficient to reliably measure the current-phase relation. Instead, we discovered that our measurement was heavily influenced by additional inductances originating from the self-formed PdTex inside the junction. We developed a method to numerically recover the current-phase relation and found that the 1.5 μm long junction was best described in the short ballistic limit. Our results highlight the complexity of subtle inductance effects that can lead to misleading topological signatures in transport measurements.
Article
Multidisciplinary Sciences
Wenjin Zhao, Bowen Shen, Zui Tao, Zhongdong Han, Kaifei Kang, Kenji Watanabe, Takashi Taniguchi, Kin Fai Mak, Jie Shan
Summary: Scientists have realized synthetic Kondo lattice in AB-stacked MoTe2/WSe2 moire bilayers, observing heavy fermions and demonstrating gate-tunable Kondo temperatures. This study opens the possibility of accessing the phase diagram of the Kondo lattice using semiconductor moire materials.
Article
Nanoscience & Nanotechnology
Kaifei Kang, Wenjin Zhao, Yihang Zeng, Kenji Watanabe, Takashi Taniguchi, Jie Shan, Kin Fai Mak
Summary: We have achieved the pulsed control of the superlattice effect in two-dimensional materials through the ferroelectric effect, switching between the correlated and superlattice insulating states, and observing the nonlinear anomalous Hall effect. This study demonstrates the potential for creating new functional superlattice materials by incorporating intrinsic symmetry-breaking orders.
NATURE NANOTECHNOLOGY
(2023)
Article
Multidisciplinary Sciences
Richen Xiong, Jacob H. Nie, Samuel L. Brantly, Patrick Hays, Renee Sailus, Kenji Watanabe, Takashi Taniguchi, Sefaattin Tongay, Chenhao Jin
Summary: We observe a bosonic correlated insulator composed of excitons in tungsten diselenide/tungsten disulfide (WSe2/WS2) moire superlattices. The insulator transitions continuously into an electron correlated insulator with varying charge density, suggesting a mixed correlated insulating state between the two limits.
Article
Materials Science, Multidisciplinary
Nikodem Sokolowski, Swaroop Palai, Mateusz Dyksik, Katarzyna Posmyk, Michal Baranowski, Alessandro Surrente, Duncan Maude, Felix Carrascoso, Onur Cakiroglu, Estrella Sanchez, Alina Schubert, Carmen Munuera, Takashi Taniguchi, Kenji Watanabe, Joakim Hagel, Samuel Brem, Andres Castellanos-Gomez, Ermin Malic, Paulina Plochocka
Summary: In this study, the influence of twist angle on momentum-indirect excitons (IXs) in a MoSe2/MoS2 heterostructure was investigated using spectroscopy and many-particle theory. It was found that increasing the twist angle led to a significant blue shift of the excitons due to dehybridization. Furthermore, for small twist angle heterostructures, two IX states were observed through photoluminescence measurements, which were attributed to transitions from different moire minibands. This research contributes to a better understanding of the hybridization of momentum-dark IX states influenced by the moire pattern, which is important for applications in moire-tronics and quantum technologies.
Article
Chemistry, Multidisciplinary
Xintong Li, Peng Zhou, Xuan Hu, Ethan Rivers, Kenji Watanabe, Takashi Taniguchi, Deji Akinwande, Joseph S. Friedman, Jean Anne C. Incorvia
Summary: Ambipolar dual-gate transistors based on low-dimensional materials enable reconfigurable logic circuits with suppressed off-state current. This article presents high-performance ambipolar dual-gate transistors based on tungsten diselenide (WSe2), which exhibit high on-off ratio, low off-state current, negligible hysteresis, and ideal subthreshold swing. Cascadable logic gates with minimal static power consumption are demonstrated using these transistors. The study also investigates the behavior of both control gate and polarity gate and analyzes the noise margin and speed performance of the circuits built by dual-gate devices. This work advances the field of ambipolar dual-gate transistors and showcases their potential for low-power, high-speed, and more flexible logic circuits.
Article
Chemistry, Multidisciplinary
Hakon Rost, Simon P. Cooil, Anna Cecilie Asland, Jinbang Hu, Ayaz Ali, Takashi Taniguchi, Kenji Watanabe, Branson D. Belle, Bodil Holst, Jerzy T. Sadowski, Federico Mazzola, Justin W. Wells
Summary: Understanding the collective behavior of quasiparticles in solid-state systems is crucial for nonvolatile electronics, allowing control of many-body effects and their applications. Hexagonal boron nitride (hBN) is a wide-energy-bandgap semiconductor with potential for low-dimensional device heterostructures. Despite its inertness, few-layer hBN shows a significant increase in electron mass, affecting the lifetime of pi-band states. The enhancement is phonon-mediated and has important implications for hBN-based devices.
Article
Chemistry, Physical
Lujun Wang, Sotirios Papadopoulos, Fadil Iyikanat, Jian Zhang, Jing Huang, Takashi Taniguchi, Kenji Watanabe, Michel Calame, Mickael L. Perrin, F. Javier Garcia de Abajo, Lukas Novotny
Summary: The authors demonstrate exciton-assisted resonant electron tunnelling in van der Waals heterostructure tunnel junctions. They reveal tunnelling mechanisms involving indirect or direct excitons and optical emission driven by inelastic electron tunnelling. The study highlights the importance of materials with well-defined interfaces and the potential for van der Waals material-based optoelectronic devices.
Article
Multidisciplinary Sciences
Xin Cong, Parisa Ali Mohammadi, Mingyang Zheng, Kenji Watanabe, Takashi Taniguchi, Daniel Rhodes, Xiao-Xiao Zhang
Summary: The study investigates the characteristics of Fermi sea screening on dark excitons in monolayer WSe2 and its correlation with carrier density. The results indicate that the photoluminescence of dark excitons shows distinct p-doping dependence when the carrier density reaches a critical level.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Lei Ren, Cedric Robert, Hanan Dery, Minhao He, Pengke Li, Dinh Van Tuan, Pierre Renucci, Delphine Lagarde, Takashi Taniguchi, Kenji Watanabe, Xiaodong Xu, Xavier Marie
Summary: We investigated charge tunable devices based on WSe2 and WS2 monolayers encapsulated in hexagonal boron nitride. We observed a weaker-intensity optical transition in photoluminescence measurements when the monolayers were electrostatically doped with electrons. Through a detailed characterization of this photoluminescence line, we identified it as an impurity-assisted radiative recombination of the intervalley negatively charged exciton (triplet trion). Our measurements also revealed the spin-orbit splitting energy difference between the emitted photons from the two possible recombination processes of the same triplet trion.
Article
Chemistry, Multidisciplinary
Tien Dat Ngo, Tuyen Huynh, Inyong Moon, Takashi Taniguchi, Kenji Watanabe, Min Sup Choi, Won Jong Yoo
Summary: This study presents a novel approach to overcome the challenges faced by 2D materials in CMOS technology, specifically in the production of high-performance p-type field effect transistors (p-FETs). By fabricating lateral p+-p-p+ junction WSe2 FETs with self-aligned TG stacks and utilizing selective oxygen plasma-doping, the researchers achieve exceptional electrostatic controllability and low power consumption in PMOS inverters.
