Editorial Material
Chemistry, Physical
Wei Yang, Guangyu Zhang
Summary: By stacking few-layer WSe2 in proximity to twisted double bilayer graphene, researchers have solid evidence of superconductivity.
Article
Physics, Multidisciplinary
Minhao He, Yuhao Li, Jiaqi Cai, Yang Liu, K. Watanabe, T. Taniguchi, Xiaodong Xu, Matthew Yankowitz
Summary: The study reveals that spontaneous symmetry breaking plays a crucial role in the correlated insulating and metallic states in twisted double bilayer graphene, which can be tuned by both the twist angle and an external electric field. The metallic states exhibit abrupt drops in resistivity as temperature decreases, suggesting that spontaneous symmetry breaking is the origin of the abrupt resistivity drops, while nonlinear transport seems to be due to Joule heating. These findings imply that similar mechanisms may be relevant across a broader class of semiconducting flat band van der Waals heterostructures.
Article
Physics, Multidisciplinary
Petar Tomic, Peter Rickhaus, Aitor Garcia-Ruiz, Giulia Zheng, Elias Portoles, Vladimir Fal'ko, Kenji Watanabe, Takashi Taniguchi, Klaus Ensslin, Thomas Ihn, Folkert K. de Vries
Summary: In this study, magnetotransport oscillations caused by scattering between minivalleys in twisted double bilayer graphene are investigated. An electron-phonon mechanism and valley conserving scattering are found to be likely mechanisms.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Carmen Rubio-Verdu, Simon Turkel, Yuan Song, Lennart Klebl, Rhine Samajdar, Mathias S. Scheurer, Jorn W. F. Venderbos, Kenji Watanabe, Takashi Taniguchi, Hector Ochoa, Lede Xian, Dante M. Kennes, Rafael M. Fernandes, Angel Rubio, Abhay N. Pasupathy
Summary: A study on twisted double bilayer graphene reveals the presence of three-fold rotational symmetry breaking, indicative of an interaction-driven electronic nematic phase that emerges from the normal metal state and is related to the scale of the moire lattice.
Article
Multidisciplinary Sciences
Peter Rickhaus, Folkert K. de Vries, Jihang Zhu, Elias Portoles, Giulia Zheng, Michele Masseroni, Annika Kurzmann, Takashi Taniguchi, Kenji Watanabe, Allan H. MacDonald, Thomas Ihn, Klaus Ensslin
Summary: This study discovered a correlated electron-hole state in double-bilayer graphene twisted to 2.37 degrees, where moire states retain much of their isolated bilayer character. This allows the generation of an energetic overlap between narrow isolated electron and hole bands with good nesting properties, leading to the formation of ordered states with reconstructed Fermi surfaces consistent with a density-wave state that can be tuned without introducing chemical dopants.
Article
Chemistry, Physical
Ruiheng Su, Manabendra Kuiri, Kenji Watanabe, Takashi Taniguchi, Joshua Folk
Summary: Identifying the essential components of superconductivity in graphene-based systems remains a critical problem in two-dimensional materials research. This field is connected to the mysteries that underpin investigations of unconventional superconductivity in condensed-matter physics. Here we report the discovery of superconductivity in twisted double bilayer graphene (TDBG) in proximity to WSe2, showing the correlation between a high density of states and the emergence of superconductivity in TDBG while revealing a possible role for isospin fluctuations in the pairing.
Article
Chemistry, Multidisciplinary
Minhao He, Jiaqi Cai, Ya-Hui Zhang, Yang Liu, Yuhao Li, Takashi Taniguchi, Kenji Watanabe, David H. Cobden, Matthew Yankowitz, Xiaodong Xu
Summary: Twisted double bilayer graphene has been studied as a platform for studying strongly correlated and topological states. In this research, a phase diagram representing these states as a function of parameters was constructed based on measurements of several devices. Symmetry-broken states were observed at a specific twist angle, including a Chern insulator state with band filling of 7/2 and an incipient state with filling of 11/3. An anomalous Hall effect was also observed at zero magnetic field in samples supporting the symmetry-broken states.
Article
Physics, Multidisciplinary
Yimeng Wang, Jonah Herzog-Arbeitman, G. William Burg, Jihang Zhu, Kenji Watanabe, Takashi Taniguchi, Allan H. MacDonald, B. Andrei Bernevig, Emanuel Tutuc
Summary: The discovery that twisted double bilayer graphene can exhibit both metallic edge transport and insulating bulk properties may be a signature of the predicted topological phase. Further characterization of the edge transport is necessary to confirm this finding.
Article
Multidisciplinary Sciences
Manabendra Kuiri, Christopher Coleman, Zhenxiang Gao, Aswin Vishnuradhan, Kenji Watanabe, Takashi Taniguchi, Jihang Zhu, Allan H. MacDonald, Joshua Folk
Summary: This study discovered a strong anomalous Hall effect in twisted double bilayer graphene, suggesting the breaking of time reversal symmetry due to orbital ferromagnetism. Gate voltages applied to the device can tune both the flatness and topology of the electronic bands, providing an unusual level of experimental control.
NATURE COMMUNICATIONS
(2022)
Article
Multidisciplinary Sciences
Canxun Zhang, Tiancong Zhu, Salman Kahn, Shaowei Li, Birui Yang, Charlotte Herbig, Xuehao Wu, Hongyuan Li, Kenji Watanabe, Takashi Taniguchi, Stefano Cabrini, Alex Zettl, Michael P. Zaletel, Feng Wang, Michael F. Crommie
Summary: The translation discusses the discovery of interaction-driven insulating and superconducting phases in moire van der Waals heterostructures, as well as presents scanning tunneling microscopy and spectroscopy study results of gate-tunable twisted double bilayer graphene devices, revealing the characteristics of the correlated system.
NATURE COMMUNICATIONS
(2021)
Article
Physics, Multidisciplinary
Zhao Liu, Ahmed Abouelkomsan, Emil J. Bergholtz
Summary: Twisted double bilayer graphene is predicted to be a versatile platform for realizing fractional Chern insulators at high temperatures, without the need for an external magnetic field, by tuning the gate potential and twist angle.
PHYSICAL REVIEW LETTERS
(2021)
Article
Materials Science, Multidisciplinary
Yujian Zhu, Yiwei Chen, Qingxin Li, Yongdao Chen, Yan Huang, Wang Zhu, Dongdong An, Junwei Song, Qikang Gan, Kaiyuan Wang, Lingnan Wei, Qijun Zong, Kenji Watanabe, Takashi Taniguchi, Haolin Wang, Li Huang, Lede Xian, Liang Sun, Geliang Yu, Lei Wang
Summary: The bandstructure of a material, governed by its lattice configuration, plays a crucial role in electron transport. Materials with field-effect tunable band, such as bilayer and rhombohedral trilayer graphene, offer more flexibility for electronic applications. In this study, we observed vertically electric-field tunable bandstructures on dual-gated twisted double bilayer graphene samples, with bandgap values continuously varying from zero to tens of milli-electron volts. We also found that the carrier transport deviates from Fermi liquid behavior within the first moire filling under both electron and hole sides. Additionally, the coupling between the two bilayer graphene layers can be turned on and off by a displacement field under a vertical magnetic field. Our results suggest that twisted double bilayer graphene with small twist angle serves as a platform for studying the evolution of multiple electric field tunable moire bands and emergent correlated electronic phases.
Article
Materials Science, Multidisciplinary
Yanbang Chu, Le Liu, Cheng Shen, Jinpeng Tian, Jian Tang, Yanchong Zhao, Jieying Liu, Yalong Yuan, Yiru Ji, Rong Yang, Kenji Watanabe, Takashi Taniguchi, Dongxia Shi, Fengcheng Wu, Wei Yang, Guangyu Zhang
Summary: In this study, experiments were conducted to investigate the temperature-linear resistivity in twisted double-bilayer graphene (TDBG) under different conditions, showing diverse behaviors such as T-linear, slope decreasing with carrier density, and maximum slope at the emergence of correlated states.
Article
Multidisciplinary Sciences
Le Liu, Shihao Zhang, Yanbang Chu, Cheng Shen, Yuan Huang, Yalong Yuan, Jinpeng Tian, Jian Tang, Yiru Ji, Rong Yang, Kenji Watanabe, Takashi Taniguchi, Dongxia Shi, Jianpeng Liu, Wei Yang, Guangyu Zhang
Summary: This study observes the emergence of new correlated insulators from spin-polarized states to valley-polarized states in twisted double bilayer graphene. The results demonstrate a potential method to achieve isospin control and obtain new phases of matter in twisted multilayer systems.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Multidisciplinary
Alessandra Canetta, Sergio Gonzalez-Munoz, Viet-Hung Nguyen, Khushboo Agarwal, Pauline de Crombrugghe de Picquendaele, Yuanzhuo Hong, Sambit Mohapatra, Kenji Watanabe, Takashi Taniguchi, Bernard Nysten, Benoit Hackens, Rebeca Ribeiro-Palau, Jean-Christophe Charlier, Oleg Victor Kolosov, Jean Spiece, Pascal Gehring
Summary: Using Ultrasonic Force Microscopy (UFM), researchers have quantified the variation of out-of-plane Young's modulus in minimally twisted double bilayer graphene (TDBG). They found a softening of the Young's modulus by 7% and 17% along single and double domain walls, respectively. This study highlights the tunability of nanomechanical properties in engineered twisted materials and opens new possibilities for future applications of designer 2D nanomechanical systems.
Article
Chemistry, Multidisciplinary
Oliver J. Burton, Zachary Winter, Kenji Watanabe, Takashi Taniguchi, Bernd Beschoten, Christoph Stampfer, Stephan Hofmann
Summary: We introduce a fast-screening descriptor approach to achieve holistic optimization of the graphene-Cu model system and successfully prepare high-quality graphene with a very high yield. Our approach is adaptable to other descriptors and 2D material systems.
Article
Chemistry, Multidisciplinary
Chia-Hao Lee, Huije Ryu, Gillian Nolan, Yichao Zhang, Yangjin Lee, Siwon Oh, Hyeonsik Cheong, Kenji Watanabe, Takashi Taniguchi, Kwanpyo Kim, Gwan-Hyoung Lee, Pinshane Y. Huang
Summary: This study investigates the phase transition mechanisms of 2D molybdenum ditelluride (MoTe2) materials and demonstrates the creation of lateral 2H-Td interfaces using laser irradiation. By using in situ heating in a transmission electron microscope (TEM), the researchers observe the phase transitions from micro-to atomic scales and find that the Td-to-2H phase transition initiates at phase boundaries at low temperatures and propagates anisotropically. The study also presents a fully reversible 2H- Td-2H phase transition cycle and provides insights for fabricating 2D heterophase devices with atomically sharp and coherent interfaces.
Article
Materials Science, Multidisciplinary
Jakob Lenz, Martin Statz, K. Watanabe, T. Taniguchi, Frank Ortmann, R. Thomas Weitz
Summary: Despite the complex nanostructure, the fundamental mechanism of charge transport through organic polymers is still unclear. In this study, we investigate charge transport at the sub-100 nm lengthscale using single poly(diketopyrrolopyrrole-terthiophene) fiber transistors with two different solid gate dielectrics. The results show near-ideal behavior at room temperature and nonlinear behavior at low temperatures, which can be explained by the formation of multiple quantum dots.
JOURNAL OF PHYSICS-MATERIALS
(2023)
Article
Physics, Applied
Yuto Urano, Mengsong Xue, Kenji Watanabe, Takashi Taniguchi, Ryo Kitaura
Summary: We study the valley coherence in high and low-quality monolayer MoSe2 using polarization-resolved photoluminescence spectroscopy. The valley coherence is approximately 10% regardless of sample quality, indicating that suppressing extrinsic effects does not improve the valley coherence. The estimated valley decoherence time, based on the valley coherence time and exciton lifetime, is sub-picosecond at the longest, suggesting that intrinsic scattering sources such as phonons strongly limit the valley coherence.
APPLIED PHYSICS EXPRESS
(2023)
Article
Chemistry, Multidisciplinary
Arka Karmakar, Tomasz Kazimierczuk, Igor Antoniazzi, Mateusz Raczynski, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, Adam Babinski, Abdullah Al-Mahboob, Maciej R. Molas
Summary: Highlight absorption and strong photoluminescence in monolayer transition metal dichalcogenides make them ideal for optoelectronic device applications. Competing interlayer charge transfer and energy transfer processes control the photocarrier relaxation pathways in these TMD heterostructures. Our experiment shows efficient energy transfer between WSe2 and MoS2 in the heterostructure with hexagonal boron nitride, resulting in enhanced MoS2 photoluminescence.
Article
Multidisciplinary Sciences
L. Banszerus, S. Moeller, K. Hecker, E. Icking, K. Watanabe, T. Taniguchi, F. Hassler, C. Volk, C. Stampfer
Summary: Particle-hole symmetry plays an important role in characterizing topological phases in solid-state systems. This study reveals that bilayer graphene exhibits nearly perfect particle-hole symmetry and has a protected single-particle spin-valley blockade, which is essential for the operation of spin and valley qubits.
Article
Nanoscience & Nanotechnology
Shen Zhao, Zhijie Li, Xin Huang, Anna Rupp, Jonas Goeser, Ilia A. Vovk, Stanislav Yu. Kruchinin, Kenji Watanabe, Takashi Taniguchi, Ismail Bilgin, Anvar S. Baimuratov, Alexander Hoegele
Summary: Moire effects in vertically stacked 2D crystals can lead to new quantum materials with rich transport and optical phenomena. However, due to finite elasticity, the superlattices can transform into periodically reconstructed patterns. In this study, the concept of lattice reconstruction is expanded to the mesoscopic scale, and its consequences in optical studies of excitons in MoSe2-WSe2 heterostructures are demonstrated.
NATURE NANOTECHNOLOGY
(2023)
Article
Multidisciplinary Sciences
Eric Anderson, Feng-Ren Fan, Jiaqi Cai, William Holtzmann, Takashi Taniguchi, Kenji Watanabe, Di Xiao, Wang Yao, Xiaodong Xu
Summary: We report in situ gate switching between honeycomb and triangular lattice geometries of an electron many-body Hamiltonian in rhombohedral (R)-stacked molybdenum ditelluride (MoTe2) moire bilayers. Our work demonstrates R-stacked MoTe2 moires to be a laboratory for engineering correlated states with nontrivial topology.
Article
Multidisciplinary Sciences
Shuo Lou, Bosai Lyu, Jiajun Chen, Lu Qiu, Saiqun Ma, Peiyue Shen, Zhichun Zhang, Yufeng Xie, Qi Liang, Kenji Watanabe, Takashi Taniguchi, Feng Ding, Zhiwen Shi
Summary: Graphene nanoribbons (GNRs) and carbon nanotubes (CNTs) are one-dimensional graphitic materials with promising applications in nanoelectronics. A generic method for the synthesis of both GNRs and CNTs, as well as their heterojunctions, has been developed using catalyzed chemical vapor deposition (CVD) on atomically flat hexagonal boron nitride (h-BN) substrates. The relative ratio of GNRs and CNTs can be controlled by adjusting the growth temperature or feeding gas pressures. Additionally, GNR/CNT intramolecular junctions were achieved by changing the H-2 partial pressure during the growth process.
SCIENTIFIC REPORTS
(2023)
Article
Materials Science, Multidisciplinary
Jan Philipp Bange, Paul Werner, David Schmitt, Wiebke Bennecke, Giuseppe Meneghini, AbdulAziz AlMutairi, Marco Merboldt, Kenji Watanabe, Takashi Taniguchi, Sabine Steil, Daniel Steil, R. Thomas Weitz, Stephan Hofmann, G. S. Matthijs Jansen, Samuel Brem, Ermin Malic, Marcel Reutzel, Stefan Mathias
Summary: The energy landscape of optical excitations in mono- and few-layer transition metal dichalcogenides (TMDs) can be dominated by optically bright and dark excitons. In this work, the researchers used femtosecond momentum microscopy combined with many-particle modeling to compare the dynamics of intralayer and hybrid excitons in different TMD systems. They found that hybrid excitons have lower energy compared to intralayer excitons, and that both types of excitons are formed via exciton-phonon scattering from optically excited bright excitons. The efficiency of phonon absorption and emission processes in these systems strongly depends on the energy alignment of the excitons with respect to the optically excited bright exciton.
Article
Nanoscience & Nanotechnology
Hai Yen Le Thi, Tien Dat Ngo, Nhat Anh Nguyen Phan, Hoseong Shin, Inayat Uddin, A. Venkatesan, Chi-Te Liang, Nobuyuki Aoki, Won Jong Yoo, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Kim
Summary: In this study, a facile and doping-free approach based on contact engineering of tungsten di-selenide was proposed to form a lateral p-n homojunction photovoltaic material. The experimental results demonstrated the great potential of this technique for next-generation optoelectronic devices.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Chemistry, Multidisciplinary
Ryan J. Gelly, Alexander D. White, Giovanni Scuri, Xing Liao, Geun Ho Ahn, Bingchen Deng, Kenji Watanabe, Takashi Taniguchi, Jelena Vuckovic, Hongkun Park
Summary: Efficient nanophotonic devices are crucial in applications such as quantum networking, optical information processing, sensing, and nonlinear optics. However, integrating two-dimensional materials into photonic structures is often limited by size and material quality. This study uses hexagonal boron nitride as a waveguiding layer to improve the optical quality of embedded films. By combining it with photonic inverse design, it provides a complete platform for interfacing with optically active 2D materials and enables various functionalities. This work opens up possibilities for advanced 2D-material nanophotonic structures in classical and quantum nonlinear optics.
Article
Chemistry, Physical
Matthieu Fortin-Deschenes, Kenji Watanabe, Takashi Taniguchi, Fengnian Xia
Summary: The unique physics in moire superlattices of twisted or lattice-mismatched atomic layers holds great promise for future quantum technologies. However, twisted configurations are thermodynamically unfavourable, making accurate twist angle control during growth implausible. While rotationally aligned, lattice-mismatched moires such as WSe2/WS2 can be synthesized, they lack the critical moire period tunability, and their formation mechanisms are not well understood. Here, we report the thermodynamically driven van der Waals epitaxy of moires with a tunable period from 10 to 45 nanometres, using lattice mismatch engineering in two WSSe layers with adjustable chalcogen ratios. Contrary to conventional epitaxy, where lattice-mismatch-induced stress hinders high-quality growth, we reveal the key role of bulk stress in moire formation and its unique interplay with edge stress in shaping the moire growth modes. Moreover, the superlattices display tunable interlayer excitons and moire intralayer excitons. Our studies unveil the epitaxial science of moire synthesis and lay the foundations for moire-based technologies.
Article
Engineering, Electrical & Electronic
Christian D. Matthus, Phanish Chava, Kenji Watanabe, Takashi Taniguchi, Thomas Mikolajick, Manfred Helm, Artur Erbe
Summary: In this study, we demonstrated the usability of a fully 2D-materials based device as a temperature sensor for linear temperature measurement at cryogenic temperatures. By applying different temperatures to the device and recording the I-V characteristics, we found that the main current flows through the device when it is reversely biased, contrary to classical expectation. We also investigated the temperature-sensor performance by applying a constant current to the device and measuring the voltage drop at different temperatures.
IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY
(2023)
Article
Chemistry, Multidisciplinary
Minhao He, Jiaqi Cai, Ya-Hui Zhang, Yang Liu, Yuhao Li, Takashi Taniguchi, Kenji Watanabe, David H. Cobden, Matthew Yankowitz, Xiaodong Xu
Summary: Twisted double bilayer graphene has been studied as a platform for studying strongly correlated and topological states. In this research, a phase diagram representing these states as a function of parameters was constructed based on measurements of several devices. Symmetry-broken states were observed at a specific twist angle, including a Chern insulator state with band filling of 7/2 and an incipient state with filling of 11/3. An anomalous Hall effect was also observed at zero magnetic field in samples supporting the symmetry-broken states.
