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
Bixuan Li, Juntian Wei, Chunqiao Jin, Kunpeng Si, Lingjia Meng, Xingguo Wang, Yangyu Jia, Qianqian He, Peng Zhang, Jinliang Wang, Yongji Gong
Summary: In this study, an intercalation strategy using organic molecules was developed to fabricate high-quality and diverse twisted bilayer graphene (tBLG). By weakening the interlayer interaction and inducing slide or rotation of the topmost graphene layer, the proportion of tBLGs in the resulting dtBLG reached up to 84.4% for twist angles ranging from 0 degrees to 30 degrees, surpassing previous methods. The twist angle distribution was found to be non-uniform, concentrating in the ranges of 0-10 degrees and 20-30 degrees. This facile and rapid intercalation-based methodology provides a practical solution for studying angle-dependent physics and advancing the utilization of twisted two-dimensional materials.
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
G. Piccinini, V Miseikis, K. Watanabe, T. Taniguchi, C. Coletti, S. Pezzini
Summary: This study demonstrates the use of dual-gated 30 degrees-twisted bilayer graphene to achieve high mobility and conductivity. The research proposes a simplified method for measuring thermodynamic quantities in graphene-based systems.
Article
Physics, Multidisciplinary
Shaowen Chen, Minhao He, Ya-Hui Zhang, Valerie Hsieh, Zaiyao Fei, K. Watanabe, T. Taniguchi, David H. Cobden, Xiaodong Xu, Cory R. Dean, Matthew Yankowitz
Summary: Twisted monolayer-bilayer graphene (tMBG) systems exhibit various correlated metallic and insulating states, as well as topological magnetic states. The phase diagram of tMBG can be switched under different perpendicular electric fields, providing a tunable platform for investigating correlated and topological states.
Article
Chemistry, Multidisciplinary
Chao Yan, Ya-Xin Zhao, Yi-Wen Liu, Lin He
Summary: This study investigates the dynamics of nanobubbles in tiny-angle twisted bilayer graphene (TBG) and reveals the significant influence of the moire superlattice on the motion of nanoscale interfacial substances.
Article
Chemistry, Physical
Ramin Ahmadi, Mohammad Taghi Ahmadi, Seyed Saeid Rahimian Koloor, Michal Petru
Summary: The research focuses on the application of twisted graphene as a new graphene structure in device technology. The study analyzes the geometry effect of twisted graphene on the operation of Schottky transistors, and explores the relationship between twist diameter and twist number.
Article
Multidisciplinary Sciences
Minhao He, Ya-Hui Zhang, Yuhao Li, Zaiyao Fei, Kenji Watanabe, Takashi Taniguchi, Xiaodong Xu, Matthew Yankowitz
Summary: The research uncovers a rich correlated phase diagram in twisted monolayer-bilayer graphene and identifies a new insulating state that can be explained by intervalley coherence with broken time reversal symmetry through electrical transport measurements.
NATURE COMMUNICATIONS
(2021)
Article
Physics, Multidisciplinary
Shuigang Xu, Mohammed M. Al Ezzi, Nilanthy Balakrishnan, Aitor Garcia-Ruiz, Bonnie Tsim, Ciaran Mullan, Julien Barrier, Na Xin, Benjamin A. Piot, Takashi Taniguchi, Kenji Watanabe, Alexandra Carvalho, Artem Mishchenko, A. K. Geim, Vladimir I. Fal'ko, Shaffique Adam, Antonio Helio Castro Neto, Kostya S. Novoselov, Yanmeng Shi
Summary: The study of electronic transport properties of twisted monolayer-bilayer graphene reveals highly tunable van Hove singularities that can cause strong correlation effects under optimum conditions by changing the twist angle or applying an electric field. This demonstrates the potential for correlated insulating states in a structure of monolayer and bilayer graphene with a small twist between them.
Article
Chemistry, Physical
Moon Jip Park, Sunam Jeon, SungBin Lee, Hee Chul Park, Youngkuk Kim
Summary: Higher-order topological insulator with topological corner states can be identified in twisted bilayer graphene systems through quantum oscillations. The tunneling of electrons between topological corner states leads to gate-tunable oscillations in the energy spectra, with oscillatory nodes indicating perfect suppression of tunneling and highlighting the topological nature of the corner states. A transport experiment is proposed for experimental realization of the oscillations, providing a feasible route to identify higher-order topological materials in twisted bilayer graphenes.
Article
Physics, Multidisciplinary
Ruirui Niu, Xiangyan Han, Zhuangzhuang Qu, Zhiyu Wang, Zhuoxian Li, Qianling Liu, Chunrui Han, Jianming Lu
Summary: Highly controlled electronic correlation in twisted graphene heterostructures has attracted significant attention recently. In this study, we investigate correlated states in an alternating twisted Bernal bilayer-monolayer-monolayer graphene and observe that van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields. Our findings also show that correlated peaks grow counterintuitively with heating and reach a maximum around 20 K, indicating the presence of the Pomeranchuk effect. This multilayer heterostructure provides new opportunities for studying correlated phenomena.
Article
Physics, Multidisciplinary
Siyu Li, Zhengwen Wang, Yucheng Xue, Lu Cao, Kenji Watanabe, Takashi Taniguchi, Hongjun Gao, Jinhai Mao
Summary: In this study, the distribution patterns of flat bands in twisted monolayer-bilayer graphene (tMBG) were observed using scanning tunneling microscopy and spectroscopy (STM/S), revealing two different modes of flat band distributions. By adjusting the electric field, the distribution of the two flat bands transitioned from a localized mode to a delocalized mode. This gate-controlled flat band wavefunction polarization is unique to the tMBG system, highlighting its potential in simulating twisted bilayer graphene (TBG) and twisted double bilayer graphene (tDBG), and exploring novel moire physics.
Article
Chemistry, Multidisciplinary
Zongqi Bai, Yang Xiao, Qing Luo, Miaomiao Li, Gang Peng, Zhihong Zhu, Fang Luo, Mengjian Zhu, Shiqiao Qin, Kostya Novoselov
Summary: The emergence of two-dimensional materials has led to important applications in electronic and optoelectronic devices. However, there are limitations such as low ON/OFF ratio and Schottky barrier formation. In this study, highly tunable field-effect tunneling transistors based on vertical graphene-WS2-graphene heterostructures were demonstrated, overcoming these limitations and achieving low off-state current, high ON/OFF ratio, and controllable carrier transport polarity.
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
Chemistry, Multidisciplinary
Zongqi Bai, Sen Zhang, Yang Xiao, Miaomiao Li, Fang Luo, Jie Li, Shiqiao Qin, Gang Peng
Summary: Van der Waals heterojunctions, formed by stacking two-dimensional materials, provide a new way for designing functional devices and exploring novel physical phenomena. In this study, bilayer graphene/WS2/metal heterojunctions with vertical architecture were fabricated and their tunneling current-bias voltage properties were investigated. The results showed that the properties of GWMHs can be tuned by a large magnitude and exhibit potential for high-power field-effect transistors and next-generation logic electronic devices.
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
Georgy Ermolaev, Anatoly P. Pushkarev, Alexey Zhizhchenko, Aleksandr A. Kuchmizhak, Ivan Iorsh, Ivan Kruglov, Arslan Mazitov, Arthur Ishteev, Kamilla Konstantinova, Danila Saranin, Aleksandr Slavich, Dusan Stosic, Elena S. Zhukova, Gleb Tselikov, Aldo Di Carlo, Aleksey Arsenin, Kostya S. Novoselov, Sergey Makarov, Valentyn S. Volkov
Summary: In recent years, the significance of giant optical anisotropy in light manipulation has been demonstrated. However, achieving continuous tunability of optical anisotropy has remained a challenge. This study presents a solution to this problem through the chemical alteration of halogen atoms in single-crystal halide perovskites, resulting in the continuous modification of optical anisotropy. Our findings also show that halide perovskites can exhibit high optical anisotropy up to 0.6 in the visible range, the highest value among non-van der Waals materials.
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
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.
