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
Chemistry, Physical
Shuang Wu, Zhenyuan Zhang, K. Watanabe, T. Taniguchi, Eva Y. Andrei
Summary: In magic-angle twisted bilayer graphene, doping-induced Lifshitz transitions and van Hove singularities lead to the emergence of correlation-induced gaps and topologically non-trivial subbands. With the presence of a magnetic field, quantized Hall plateaus reveal the subband topology and signal the emergence of Chern insulators with Chern numbers. Additionally, a van Hove singularity at a filling of 3.5 suggests the possibility of a fractional Chern insulator, accompanied by a crossover from low-temperature metallic to high-temperature insulating behavior.
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
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
Dumitru Calugaru, Nicolas Regnault, Myungchul Oh, Kevin P. Nuckolls, Dillon Wong, Ryan L. Lee, Ali Yazdani, Oskar Vafek, B. Andrei Bernevig
Summary: This article analytically computes the scanning tunneling microscopy (STM) signatures of integer-filled correlated ground states of the magic angle twisted bilayer graphene (TBG) narrow bands and assesses the possibility of Kekule distortion (KD). The results show that coupling the two opposite graphene valleys does not always result in KD.
PHYSICAL REVIEW LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Ipsita Mandal, Jia Yao, Erich J. Mueller
Summary: Experiments have shown that insulating behavior emerges in graphene bilayers when the moire bands are partially filled and the top layer is rotated relative to the bottom layer. By calculating charge distributions and estimating excitation gaps, researchers are able to further understand the properties of these phases.
Article
Multidisciplinary Sciences
Jiang-Xiazi Lin, Ya-Hui Zhang, Erin Morissette, Zhi Wang, Song Liu, Daniel Rhodes, K. Watanabe, T. Taniguchi, James Hone, J. I. A. Li
Summary: This study investigates the combined influence of strong electron correlation and spin-orbit coupling on a two-dimensional electronic system at the interface between twisted bilayer graphene and tungsten diselenide crystal. The research shows that strong electron correlation stabilizes correlated insulating states at different fillings within the moire flatband and spin-orbit coupling transforms these insulators into ferromagnetic materials. The coupling between spin and valley degrees of freedom can be controlled with a magnetic or electric field.
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
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
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
Materials Science, Multidisciplinary
Frank Schindler, Oskar Vafek, B. Andrei Bernevig
Summary: The strong-coupling phase diagram of magic-angle twisted bilayer graphene predicts exact one-particle charge +/- 1 gapped excitations above the ferromagnetic ground states. In this study, the trion bound state is identified as the lowest charge +1 overall excitation under certain conditions.
Article
Physics, Multidisciplinary
Krystof Kolar, Gal Shavit, Christophe Mora, Yuval Oreg, Felix von Oppen
Summary: The emergence of correlated insulating phases in magic-angle twisted bilayer graphene is highly dependent on the sample. We derive an Anderson theorem that describes the robustness of the Kramers intervalley coherent (K-IVC) state against PT (particle-hole conjugation) and time reversal perturbations, which is a prime candidate for describing correlated insulators at even fillings of the moire flat bands. We find that the K-IVC gap is robust against PT-odd perturbations, but PT-even perturbations can induce subgap states and reduce or eliminate the gap. This result allows us to classify the stability of the K-IVC state against experimentally relevant perturbations.
PHYSICAL REVIEW LETTERS
(2023)
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
Multidisciplinary Sciences
Si-yu Li, Zhengwen Wang, Yucheng Xue, Yingbo Wang, Shihao Zhang, Jianpeng Liu, Zheng Zhu, Kenji Watanabe, Takashi Taniguchi, Hong-jun Gao, Yuhang Jiang, Jinhai Mao
Summary: Researchers observed an electron crystal phase and studied the coupling between strong electron correlation and nontrivial band topology in twisted monolayer-bilayer graphene using scanning tunnelling microscopy.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
S. Hubmann, G. Di Battista, I. A. Dmitriev, K. Watanabe, T. Taniguchi, D. K. Efetov, S. D. Ganichev
Summary: In this study, the infrared photoresistance of twisted bilayer graphene (tBLG) under continuous quantum cascade laser illumination at a frequency of 57.1 THz was observed. The photoresistance exhibited a complex sign-alternating behavior under variations of temperature and back gate voltage, and showed giant resonance-like enhancements at certain gate voltages. The structure of the photoresponse correlated with weaker features in the dark dc resistance, indicating the complex band structure of tBLG. The observed photoresistance was well explained by a bolometric model, suggesting ultrafast thermalization of the photoexcited electron-hole pairs across different temperatures and gate voltages. This study establishes photoresistance as a highly sensitive probe for temperature variations in electronic transport of tBLG.
Article
Physics, Applied
Takato Hotta, Haruna Nakajima, Shohei Chiashi, Taiki Inoue, Shigeo Maruyama, Kenji Watanabe, Takashi Taniguchi, Ryo Kitaurat
Summary: In this study, trions have been successfully confined in a one-dimensional restricted space of a MoSe2 device using carbon nanotube (CNT) gate electrodes. The dry transfer process, including deterministic dry transfer of aligned CNTs, has resulted in an hBN-encapsulated MoSe2 device with CNT back gate electrodes. Applying voltage via CNT gate electrodes significantly alters the PL spectra at the location with CNT gate electrodes, which is not observed at a location without CNT gate electrodes. PL imaging shows that the image contrast from trions along the CNT electrode underneath is linear, indicating the one-dimensional confinement of trions in response to the CNT local gating. The obtained confinement width from the PL image is 5.5 x 10(2) nm, consistent with nanoscale one-dimensional confined trions with diffraction limit broadening. This work demonstrates the electrical control of excitonic states at the nanoscale, leading to potential novel optoelectronic properties and exciton devices in the future.
APPLIED PHYSICS EXPRESS
(2023)
Correction
Multidisciplinary Sciences
Sein Park, Wonjun Lee, Seong Jang, Yong-Bin Choi, Jinho Park, Woochan Jung, Kenji Watanabe, Takashi Taniguchi, Gil Young Cho, Gil-Ho Lee
Article
Chemistry, Multidisciplinary
Souvik Biswas, Aurelie Champagne, Jonah B. Haber, Supavit Pokawanvit, Joeson Wong, Hamidreza Akbari, Sergiy Krylyuk, Kenji Watanabe, Takashi Taniguchi, Albert Davydov, Zakaria Y. Al Balushi, Diana Y. Qiu, Felipe H. da Jornada, Jeffrey B. Neaton, Harry A. Atwater
Summary: This study experimentally investigates the excitonic luminescence properties of monolayer MoTe2 and reveals the temperature dependence and interplay between exciton and trion. The results demonstrate that these properties are influenced by free-carrier screening, Pauli blocking, and band gap renormalization, in agreement with theoretical calculations. These findings contribute to the potential applications of monolayer MoTe2 in near-infrared optoelectronics and photonic devices.
Article
Chemistry, Multidisciplinary
Raj Katti, Harpreet Singh Arora, Olli-Pentti Saira, Kenji Watanabe, Takashi Taniguchi, Keith C. Schwab, Michael Lee Roukes, Stevan Nadj-Perge
Summary: Graphene is a crucial material for bolometry, calorimetry, and photon detection due to its exceptional electronic and thermal properties. However, the physical processes responsible for heat transport from electrons to lattice in graphene are still not well understood. In this study, researchers measured the thermal response of low-disorder graphene encapsulated in hexagonal boron nitride and integrated it within a multiterminal superconducting microwave resonator. Their findings suggest that the thermalization rates of electrons and holes in graphene can be attributed to processes at the graphene-aluminum interface.
Article
Chemistry, Physical
Cequn Li, Yi-Fan Zhao, Alexander Vera, Omri Lesser, Hemian Yi, Shalini Kumari, Zijie Yan, Chengye Dong, Timothy Bowen, Ke Wang, Haiying Wang, Jessica L. Thompson, Kenji Watanabe, Takashi Taniguchi, Danielle Reifsnyder Hickey, Yuval Oreg, Joshua A. Robinson, Cui-Zu Chang, Jun Zhu
Summary: We report on the growth and properties of high-quality (Bi,Sb)(2)Te-3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, promoting proximity-induced superconductivity originating in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states, and the presence of a single Abrikosov vortex manifesting in discrete conductance changes.
Article
Physics, Multidisciplinary
A. Schmitt, P. Vallet, D. Mele, M. Rosticher, T. Taniguchi, K. Watanabe, E. Bocquillon, G. Feve, J. M. Berroir, C. Voisin, J. Cayssol, M. O. Goerbig, J. Troost, E. Baudin, B. Placais
Summary: Researchers have achieved a mesoscopic variant of the Schwinger effect in graphene transistors, which involves the creation of matter by electric fields. By conducting transport measurements, they observed universal one-dimensional Schwinger conductance at the pinch-off of the transistors. These findings enhance our understanding of current saturation limits in ballistic graphene and open up new directions for quantum electrodynamic experiments in the laboratory.
Article
Multidisciplinary Sciences
Saroj B. Chand, John M. Woods, Jiamin Quan, Enrique Mejia, Takashi Taniguchi, Kenji Watanabe, Andrea Alu, Gabriele Grosso
Summary: This study demonstrates the efficient diffusion of dark excitons in non-uniform materials and their propagation through optical readout, providing a new concept for excitonic device applications in both classical and quantum information technology.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Lucja Kipczak, Artur O. Slobodeniuk, Tomasz Wozniak, Mukul Bhatnagar, Natalia Zawadzka, Katarzyna Olkowska-Pucko, Magdalena Grzeszczyk, Kenji Watanabe, Takashi Taniguchi, Adam Babinski, Maciej R. Molas
Summary: Excitons in thin layers of semiconducting transition metal dichalcogenides are highly affected by the modified electron-hole interaction, leading to deviations from the two-dimensional hydrogen atom model. In this study, we experimentally and theoretically investigate excitonic properties in ML and BL MoSe2 encapsulated in hexagonal BN. The magnetic field evolutions of the reflectance contrast spectra were measured, allowing the determination of g-factors for intralayer and interlayer excitons. First principles calculations were used to explain the dependence of g-factors on the number of layers and excitation state. Additionally, the ladder of excitonic s states in the ML could be reproduced using the k.p 2 BL.
Article
Chemistry, Multidisciplinary
Nam Thanh Trung Vu, Leyi Loh, Yuan Chen, Qingyun Wu, Ivan A. A. Verzhbitskiy, Kenji Watanabe, Takashi Taniguchi, Michel Bosman, Yee Sin Ang, Lay Kee Ang, Maxim Trushin, Goki Eda
Summary: Precisely controlled impurity doping is essential in modern semiconductor technologies, and desired properties can be achieved at very low concentrations. However, in two-dimensional semiconductors, the identification and quantification of impurities are challenging due to their dilute limit and the limitations of common analytical techniques. In this study, we utilize conductive atomic force microscopy to rapidly and accurately image dilute single atomic impurities. The local conductivity is enhanced by more than 100-fold due to resonance-assisted tunneling, and the imaging is selective for minority defects. We also demonstrate the detection of subsurface impurities with single monolayer depth resolution in multilayer materials.
Article
Chemistry, Multidisciplinary
Shan-Wen Cheng, Ding Xu, Haowen Su, James M. Baxter, Luke N. Holtzman, Kenji Watanabe, Takashi Taniguchi, James C. Hone, Katayun Barmak, Milan Delor
Summary: In this study, we use excitons in two-dimensional materials as sensors to achieve visible-light imaging of phonon polariton propagation in hexagonal boron nitride, and observe the phenomenon of co-propagation of excitons and phonon polaritons. This research provides a new method for high-precision imaging of polar excitations and a new mechanism for realizing ballistic exciton transport at room temperature.
Article
Physics, Multidisciplinary
Liam A. Cohen, Noah L. Samuelson, Taige Wang, Kai Klocke, Cian C. Reeves, Takashi Taniguchi, Kenji Watanabe, Sagar Vijay, Michael P. Zaletel, Andrea F. Young
Summary: In an all-van der Waals heterostructure, the active layer, gate dielectrics and gate electrodes are assembled from two-dimensional crystals that have a low density of atomic defects. A resist-free local anodic oxidation process allows patterning of sub-100 nm features in graphite gates, and their subsequent integration into an all-van der Waals heterostructure. This technique enables precise control of electrons in two-dimensional materials by eliminating unwanted contamination and introducing nanoscale electrostatic control.
Article
Multidisciplinary Sciences
Samra Husremovic, Berit H. Goodge, Matthew P. Erodici, Katherine Inzani, Alberto Mier, Stephanie M. Ribet, Karen C. Bustillo, Takashi Taniguchi, Kenji Watanabe, Colin Ophus, Sinead M. Griffin, D. Kwabena Bediako
Summary: In this study, researchers demonstrate high-density phase change memory based on phase transition materials. By fabricating H-TaS2/1T-TaS2 heterostructures, they observe optically active heterochirality and correlate it with resistivity steps in the CDW superlattice structure. They also show the role of strain engineering in promoting multi-level switching.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
T. Johnsen, C. Schattauer, S. Samaddar, A. Weston, M. J. Hamer, K. Watanabe, T. Taniguchi, R. Gorbachev, F. Libisch, M. Morgenstern
Summary: Researchers used scanning tunneling microscopy to investigate the quantum Hall edge states of monolayer graphene and compared the results with theoretical calculations. They found that a proper choice of gate voltage allowed for accurate mapping of the edge state pattern, and observed extended compressible regions, the antinodal structure of edge states, and their meandering along the lateral interface.
Article
Chemistry, Multidisciplinary
Adam Krzysztof Szczerba, Julia Kucharek, Jan Pawlowski, Takashi Taniguchi, Kenji Watanabe, Wojciech Pacuski
Summary: We investigated the possibility of growing a three-dimensional semiconductor on a two-dimensional substrate, and successfully reported for the first time the growth of CdTe quantum wells on hBN using molecular beam epitaxy. The presence of the quantum wells was confirmed through photoluminescence measurements, and it was found that growth on the nearly flat hBN substrate was significantly different from growth on bulk substrates, requiring much lower temperatures.