Article
Multidisciplinary Sciences
Yonglong Xie, Andrew T. Pierce, Jeong Min Park, Daniel E. Parker, Eslam Khalaf, Patrick Ledwith, Yuan Cao, Seung Hwan Lee, Shaowen Chen, Patrick R. Forrester, Kenji Watanabe, Takashi Taniguchi, Ashvin Vishwanath, Pablo Jarillo-Herrero, Amir Yacoby
Summary: Fractional Chern insulators (FCIs) are lattice analogues of fractional quantum Hall states and have been recently observed in magic-angle twisted BLG at low magnetic field. The appearance of these states at 5 T is accompanied by the disappearance of nearby topologically trivial charge density wave states.
Article
Multidisciplinary Sciences
Youngjoon Choi, Hyunjin Kim, Yang Peng, Alex Thomson, Cyprian Lewandowski, Robert Polski, Yiran Zhang, Harpreet Singh Arora, Kenji Watanabe, Takashi Taniguchi, Jason Alicea, Stevan Nadj-Perge
Summary: Magic-angle twisted bilayer graphene (MATBG) exhibits a variety of correlated phenomena, and new techniques introduced can determine the topological phases that emerge in MATBG in a finite magnetic field. These topological phases form only in a specific range of twist angles and are influenced by strong electronic interactions.
Article
Materials Science, Multidisciplinary
Yajuan Cheng, Zheyong Fan, Tao Zhang, Masahiro Nomura, Sebastian Volz, Guimei Zhu, Baowen Li, Shiyun Xiong
Summary: We report a local minimum in thermal conductivity in twisted bilayer graphene (TBG) at the angle of 1.08 degrees, which corresponds to the 'magic angle' in the transition of several other reported properties. The thermal magic angle arises from the competition between the delocalization of atomic vibrational amplitudes and stresses on one hand, and the increased AA stacking density on the other hand. The manifestation of a magic angle, disclosing new thermal mechanisms at nanoscale, further uncovers the unique physics of two-dimensional materials.
MATERIALS TODAY PHYSICS
(2023)
Article
Multidisciplinary Sciences
Andreij C. Gadelha, Douglas A. A. Ohlberg, Cassiano Rabelo, Eliel G. S. Neto, Thiago L. Vasconcelos, Joao L. Campos, Jessica S. Lemos, Vinicius Ornelas, Daniel Miranda, Rafael Nadas, Fabiano C. Santana, Kenji Watanabe, Takashi Taniguchi, Benoit van Troeye, Michael Lamparski, Vincent Meunier, Viet-Hung Nguyen, Dawid Paszko, Jean-Christophe Charlier, Leonardo C. Campos, Luiz G. Cancado, Gilberto Medeiros-Ribeiro, Ado Jorio
Summary: The twisted bilayer graphene undergoes self-organized lattice reconstruction, resulting in the formation of a superlattice that modulates vibrational and electronic structures, leading to phenomena such as strong correlations and superconductivity. Although experimental techniques and theoretical models face challenges in observing and describing these effects, nano-Raman spectroscopy can localize some vibrational modes and provide insights into the effects of electron-phonon coupling on the material properties.
Article
Multidisciplinary Sciences
Myungchul Oh, Kevin P. Nuckolls, Dillon Wong, Ryan L. Lee, Xiaomeng Liu, Kenji Watanabe, Takashi Taniguchi, Ali Yazdani
Summary: Recent studies on magic-angle twisted bilayer graphene (MATBG) have shown that the superconductivity in MATBG may not be described by the conventional BCS theory, but rather resembles a non-BCS mechanism due to the large density of states in its flat bands. This suggests that the pairing mechanism in MATBG may be unconventional and different from that of conventional superconductors.
Article
Chemistry, Multidisciplinary
Giorgio Di Battista, Paul Seifert, Kenji Watanabe, Takashi Taniguchi, Kin Chung Fong, Alessandro Principi, Dmitri K. Efetov
Summary: In this study, the thermal properties of superconducting MATBG were revealed by monitoring its temperature dependent critical current. The temperature dependence of the electronic thermal conductance was extracted, laying the foundation for future thermal transport studies on this system.
Article
Multidisciplinary Sciences
Xiaoxue Liu, Zhi Wang, K. Watanabe, T. Taniguchi, Oskar Vafek, J. I. A. Li
Summary: This study introduces a new device geometry to continuously tune the strength of electron-electron Coulomb interaction within twisted bilayer graphene, revealing opposite effects of charge screening on insulating and superconducting states.
Article
Chemistry, Multidisciplinary
Andreij C. Gadelha, Viet-Hung Nguyen, Eliel G. S. Neto, Fabiano Santana, Markus B. Raschke, Michael Lamparski, Vincent Meunier, Jean-Christophe Charlier, Ado Jorio
Summary: This study investigates the importance of phonons in twisted-bilayer graphene at the magic-angle using gate-dependent micro-Raman spectroscopy. The results reveal that the unique electronic structure at the magic-angle influences the electron-phonon coupling, resulting in a larger G band line width.
Article
Physics, Condensed Matter
Thi-Nga Do, Po-Hsin Shih, Godfrey Gumbs
Summary: The magic-angle twisted bilayer graphene (MATBLG) with special flat bands exhibits exotic physical properties, but exploiting the engineering of these properties by external fields is still in its early stages. We show that MATBLG under an external magnetic field presents a distinctive magnetoplasmon dispersion, which can be significantly modified by transferred momentum and charge doping. Special pronounced single magnetoplasmon and horizontal single-particle excitation modes near charge neutrality exist along a wide range of transferred momentum. We provide an insightful discussion of these unique features based on the electronic excitation of Landau levels quantized from the flat bands and Landau damping. Additionally, charge doping leads to peculiar multiple strong-weight magnetoplasmons. These characteristics make MATBLG a favorable candidate for plasmonic devices and technology applications.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2023)
Article
Chemistry, Multidisciplinary
Xiaoqian Liu, Ran Peng, Zhaoru Sun, Jianpeng Liu
Summary: In this study, the phonon properties of magic-angle twisted bilayer graphene (TBG) were investigated using many-body classical potential and interatomic forces generated by a deep neural network. Various vibrational patterns and their effects on electronic structures were discovered.
Article
Materials Science, Multidisciplinary
Disha Arora, Deepanshu Aggarwal, Sankalpa Ghosh, Rohit Narula
Summary: We investigate the polarization-controlled Rayleigh scattering response of twisted bilayer graphene (tBLG) by considering the effects of structural corrugation, doping-dependent Hartree interactions, and particle-hole asymmetry. It is found that the dominant wave vectors for the Rayleigh scattering process come from different regions of the moire Brillouin zone (MBZ), in contrast to single-layer graphene (SLG) and AB-stacked bilayer graphene (AB-BLG). The integrated Rayleigh intensity is significantly enhanced for small twist angles, and the corrugation effects have a strong impact on the polarization-dependent scattering response.
Article
Physics, Multidisciplinary
Pawel Potasz, Ming Xie, A. H. MacDonald
Summary: This study reports on finite-size exact-diagonalization calculations in a Hilbert space defined by the continuum-model flat moire bands of magic angle twisted bilayer graphene, showing evidence of a spin ferromagnet ground state for moire band filling between 3 and 2, and Chern insulator ground states with spontaneous spin, valley, and sublattice polarization near filling 3. It is emphasized that the inclusion of remote band self-energy is crucial for a reliable description of flat band correlations in magic angle twisted bilayer graphene.
PHYSICAL REVIEW LETTERS
(2021)
Article
Chemistry, Physical
Nathanael P. Kazmierczak, Madeline Van Winkle, Colin Ophus, Karen C. Bustillo, Stephen Carr, Hamish G. Brown, Jim Ciston, Takashi Taniguchi, Kenji Watanabe, D. Kwabena Bediako
Summary: Twisted bilayer graphene exhibits two-regime reconstruction mechanics based on twist angle, with applied heterostrain accumulating anisotropically in saddle-point regions to generate distinctive striped strain phases. Nanoscale spatial fluctuations in twist angle and uniaxial heterostrain were statistically evaluated, revealing the prevalence of short-range disorder in moire heterostructures. This study provides insights into the twist-angle-dependent electronic behavior and structural relaxation, disorder, and strain in moire materials.
Article
Physics, Multidisciplinary
Alexina Ollier, Marcin Kisiel, Xiaobo Lu, Urs Gysin, Martino Poggio, Dmitri K. Efetov, Ernst Meyer
Summary: This study investigates the low-temperature nanomechanical energy dissipation of twisted bilayer graphene using pendulum atomic force microscopy. The authors observe different doping regions and wavefunction interference between these regions.
COMMUNICATIONS PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Ayush Singh, Colin Benjamin
Summary: The research team designed a highly efficient quantum Otto engine using twisted bilayer graphene, and found that the maximum power output efficiency occurs at the magic angle, potentially advancing the performance of nanoscale devices.
Article
Nanoscience & Nanotechnology
Aditya Sood, Jonah B. Haber, Johan Carlstrom, Elizabeth A. Peterson, Elyse Barre, Johnathan D. Georgaras, Alexander H. M. Reid, Xiaozhe Shen, Marc E. Zajac, Emma C. Regan, Jie Yang, Takashi Taniguchi, Kenji Watanabe, Feng Wang, Xijie Wang, Jeffrey B. Neaton, Tony F. Heinz, Aaron M. Lindenberg, Felipe H. da Jornada, Archana Raja
Summary: In this study, lattice dynamics in photoexcited WSe2/WS2 heterostructures were directly visualized using femtosecond electron diffraction. It was found that both WSe2 and WS2 were heated simultaneously on a picosecond timescale, which cannot be explained by phonon transport across the interface. First-principles calculations revealed a fast channel involving layer-hybridized electronic states, enabling phonon-assisted interlayer transfer of photoexcited electrons. Phonons were emitted in both layers on the femtosecond timescale via this channel, consistent with the simultaneous lattice heating observed experimentally. Strong electron-phonon coupling via layer-hybridized electronic states was identified as a novel route for controlling energy transport across atomic junctions.
NATURE NANOTECHNOLOGY
(2023)
Article
Chemistry, Multidisciplinary
Jonas D. D. Ziegler, Yeongsu Cho, Sophia Terres, Matan Menahem, Takashi Taniguchi, Kenji Watanabe, Omer Yaffe, Timothy C. C. Berkelbach, Alexey Chernikov
Summary: 2D hybrid perovskites have attracted significant attention in material research for light-harvesting and -emitting applications. In this study, a method of interfacing ultrathin sheets of perovskites with few-layer graphene and hexagonal boron nitride is demonstrated, enabling gate-tunable control of light emission and absorption. The findings reveal the emergence of both negatively and positively charged excitons, with high binding energies and excellent mobility. This research introduces the physics of interacting mixtures of optical and electrical excitations to the broad family of 2D inorganic-organic nanostructures, highlighting the potential of 2D perovskites as a promising material platform for electrically modulated light-emitters and exciton transistors.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Physical
Minwook Kim, Yeonjae Lee, Sunil Kumar, Dongwoon Kang, Sohee Lee, Van Huy Nguyen, Dinh Cong Nguyen, Syed Hassan Abbas Jaffery, Jongwan Jung, Takashi Taniguchi, Kenji Watanabe, Yongho Seo
Summary: In recent years, there has been extensive research on 2D materials-based heterostructures for fabricating nanodevices. Transition metal dichalcogenides (TMDC), hexagonal boron nitride (hBN), and graphene (Gr) are commonly used materials in these devices. Optoelectronic memory devices based on 2D materials are of particular interest due to their structural flexibility and small device size. This study focuses on the fabrication of a non-volatile optoelectronic memory device using tungsten diselenide (WSe2) and hBN-encapsulated Gr-based heterostructures. The device can be easily controlled by both UV light and an electric field.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Multidisciplinary
Valerie Hsieh, Dorri Halbertal, Nathan R. . Finney, Ziyan Zhu, Eli Gerber, Michele Pizzochero, Emine Kucukbenli, Gabriel R. Schleder, Mattia Angeli, Kenji Watanabe, Takashi Taniguchi, Eun-Ah Kim, Efthimios Kaxiras, James Hone, Cory R. Dean, D. N. Basov
Summary: Twisted van der Waals multilayers are regarded as a rich platform for accessing novel electronic phases. This study proposes that naturally formed stacking domains due to relative twist between layers can act as an additional control knob. The researchers observe selective adhesion of metallic nanoparticles and liquid water at domains with specific stacking configurations and demonstrate the manipulation of nanoparticles can locally reconfigure the moire superlattice.
Article
Chemistry, Multidisciplinary
Yu-Chiang Hsieh, Zhen-You Lin, Shin-Ji Fung, Wen-Shin Lu, Sheng-Chin Ho, Siang-Ping Hong, Sheng-Zhu Ho, Chiu-Hua Huang, Kenji Watanabe, Takashi Taniguchi, Yang-Hao Chan, Yi-Chun Chen, Chung-Lin Wu, Tse-Ming Chen
Summary: By creating atomically flat surface nanostructures in hexagonal boron nitride, we achieve an arbitrary on-chip control of both the strain distribution and magnitude on high-quality molybdenum disulfide. The phonon and exciton emissions vary according to our strain field designs, enabling us to write and draw any photoluminescence color image in a single chip. Our strain engineering also offers a powerful means to alter the strengths and energies of interlayer excitons at room temperature, promising for functional excitonic devices.
Article
Chemistry, Physical
Benjamin A. Foutty, Jiachen Yu, Trithep Devakul, Carlos R. Kometter, Yang Zhang, Kenji Watanabe, Takashi Taniguchi, Liang Fu, Benjamin E. Feldman
Summary: By studying twisted double-bilayer WSe2, we have identified charge-ordered phases at multiple integer and fractional moire fillings. Through experiments with magnetic fields and displacement fields, we have observed spin-polarized ground states and a metal-insulator transition. These results demonstrate the control over spin and valley character in this system.
Article
Multidisciplinary Sciences
Kaining Yang, Xiang Gao, Yaning Wang, Tongyao Zhang, Yuchen Gao, Xin Lu, Shihao Zhang, Jianpeng Liu, Pingfan Gu, Zhaoping Luo, Runjie Zheng, Shimin Cao, Hanwen Wang, Xingdan Sun, Kenji Watanabe, Takashi Taniguchi, Xiuyan Li, Jing Zhang, Xi Dai, Jian-Hao Chen, Yu Ye, Zheng Han
Summary: The authors report the evidence of unconventional correlated insulating states in bilayer graphene/CrOCl heterostructures and demonstrate their application for low-temperature logic inverters. They investigate the heterostructures based on Bernal-stacked bilayer graphene atop few-layered CrOCl, which exhibit an over-1-G omega-resistance insulating state in a widely accessible gate voltage range. By applying an in-plane electric field, heating, or gating, the insulating state can be switched into a metallic state with an on/off ratio up to 10(7).
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Salvatore Cianci, Elena Blundo, Federico Tuzi, Giorgio Pettinari, Katarzyna Olkowska-Pucko, Eirini Parmenopoulou, Djero B. L. Peeters, Antonio Miriametro, Takashi Taniguchi, Kenji Watanabe, Adam Babinski, Maciej R. Molas, Marco Felici, Antonio Polimeni
Summary: This paper reports the formation of regular arrays of strained hydrogen-filled one-layer-thick micro-domes by H-ion irradiation and lithography-based approaches. By depositing thin hBN flakes on the domes, the dome structure can be preserved, leading to the appearance of intense emission lines from localized excitons, which behave as quantum emitters.
ADVANCED OPTICAL MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Michael D. Randle, Masayuki Hosoda, Russell S. Deacon, Manabu Ohtomo, Patrick Zellekens, Kenji Watanabe, Takashi Taniguchi, Shota Okazaki, Takao Sasagawa, Kenichi Kawaguchi, Shintaro Sato, Koji Ishibashi
Summary: Systems combining superconductors with topological insulators provide a platform for studying Majorana bound states and realizing fault tolerant topological quantum computation. Monolayers of WTe2 possess rare properties, such as being a quantum spin Hall insulator and easily transitioning into a superconducting state. Measurements on gate-defined Josephson weak-link devices made from monolayer WTe2 demonstrate the critical role of 2D superconducting leads in interpreting magnetic interference in the resulting junctions. The reported fabrication procedures offer a straightforward means of producing more devices from this technically challenging material and mark the first step towards versatile all-in-one topological Josephson weak-links using monolayer WTe2.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Rafael Battistella Nadas, Andreij C. Gadelha, Tiago C. Barbosa, Cassiano Rabelo, Thiago de Lourenco e Vasconcelos, Vitor Monken, Ary V. R. Portes, Kenji Watanabe, Takashi Taniguchi, Jhonattan C. Ramirez, Leonardo C. Campos, Riichiro Saito, Luiz Gustavo Cancado, Ado Jorio
Summary: The coherence length (L(c)) of the Raman scattering process in graphene, as determined by spatially coherent tip-enhanced Raman spectroscopy, decreases when the Fermi energy is brought to the neutrality point. This observation is consistent with the concept of the Kohn anomaly within a ballistic transport regime. The observed results can be attributed to either an unusually large variation in the longitudinal optical phonon group velocity (v(g)), which reaches twice the value of the longitudinal acoustic phonon, or changes in the electron energy uncertainty. These properties are important for understanding optical and transport phenomena that may not be observable with other techniques.
Editorial Material
Multidisciplinary Sciences
Qian Song, Connor A. Occhialini, Emre Ergecen, Batyr Ilyas, Danila Amoroso, Paolo Barone, Jesse Kapeghian, Kenji Watanabe, Takashi Taniguchi, Antia S. Botana, Silvia Picozzi, Nuh Gedik, Riccardo Comin
Article
Optics
Tianqi Liu, Qiang Fu, Yuanzhe Li, Xu Han, Shixuan Wang, Takashi Taniguchi, Kenji Watanabe, Dongyang Wan, Qi Zhang, Yingbo Zhao, Zhenhua Ni, Fei Ding, Zhenliang Hu, Xueyong Yuan, Junpen Lu
Summary: In this study, the brightness of WS2-based LEDs is enhanced by introducing self-assembled silver nanoparticles (NPs) on top of the LED. With the assistance of effective transient-mode charge injection, a 2.9-fold electroluminescence (EL) enhancement is observed in the experiment. Full-wave simulations confirm that the improvement comes from the scattering capability of silver NPs.
Article
Optics
Garima Gupta, Kenji Watanabe, Takashi Taniguchi, Kausik Majumdar
Summary: In monolayer transition metal dichalcogenide semiconductors, valley coherence degrades rapidly due to scattering and inter-valley exchange interaction. However, by using a sandwich structure of monolayer MoS2 between top and bottom graphene, fully valley-coherent excitons with high degree of linear polarization are achieved. This is attributed to the suppression in exchange interaction, reduction in exciton lifetime, and operating in the motional narrowing regime.
LIGHT-SCIENCE & APPLICATIONS
(2023)
Article
Chemistry, Multidisciplinary
Shaochun Zhang, Mina Maruyama, Susumu Okada, Mengsong Xue, Kenji Watanabe, Takashi Taniguchi, Kazuki Hashimoto, Yasumitsu Miyata, Ruben Canton-Vitoria, Ryo Kitaura
Summary: This study reports the observation of the photovoltaic effect in a WS2/MoS2 van der Waals heterostructure. Light excitation of WS2/MoS2 at a wavelength of 633 nm leads to a photocurrent without applying bias voltages.
Article
Chemistry, Multidisciplinary
Aparna Parappurath, Bhaskar Ghawri, Saisab Bhowmik, Arup Singha, K. Watanabe, T. Taniguchi, Arindam Ghosh
Summary: The ability to tune the twist angle between different layers of 2D materials has led to the creation of electronic flat bands artificially. In this study, the photoresponse of a few-layer WSe2/tBLG heterostructure was measured, and it was found that the photoresponse is sensitive to the band structure of tBLG. When the Fermi energy is within the low-energy moiré bands, the photoresponse is strongly suppressed, but it can be recovered when the Fermi energy exceeds the moiré band edge due to the photogating effect.