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Electroluminescence from pure resonant states in hBN-based vertical tunneling junctions

Light(Science & Applications) 2024年第8期13卷 1557-1564页

作者： Magdalena Grzeszczyk Kristina Vaklinova Kenji Watanabe takashi taniguchi Konstantin SNovoselov Maciej Koperski Institute for Functional Intelligent Materials National University of SingaporeSingapore 117544Singapore Research Center for Functional Materials National Institute for Materials ScienceTsukuba 305-0044Japan International Center for Materials Nanoarchitectonics National Institute for Materials ScienceTsukuba 305-0044Japan Department of Materials Science and Engineering National University of SingaporeSingapore 117575Singapore

Defect centers in wide-band-gap crystals have garnered interest for their potential in applications among optoelectronic and sensor ***,defects embedded in highly insulating crystals,like diamond,silicon carbide,or aluminum oxide,have been notoriously difficult to excite electrically due to their large internal *** address this challenge,we realized a new paradigm of exciting defects in vertical tunneling junctions based on carbon centers in hexagonal boron nitride(hBN).The rational design of the devices via van der Waals technology enabled us to raise and control optical processes related to defect-to-band and intradefect *** fundamental understanding of the tunneling events was based on the transfer of the electronic wave function amplitude between resonant defect states in hBN to the metallic state in graphene,which leads to dramatic changes in the characteristics of electrons due to different band structures of constituent *** our devices,the decay of electrons via tunneling pathways competed with radiative recombination,resulting in an unprecedented degree of tuneability of carrier dynamics due to the significant sensitivity of the characteristic tunneling times on the thickness and structure of the *** enabled us to achieve a high-efficiency electrical excitation of intradefect transitions,exceeding by several orders of magnitude the efficiency of optical excitation in the sub-band-gap *** work represents a significant advancement towards a universal and scalable platform for electrically driven devices utilizing defect centers in wide-band-gap crystals with properties modulated via activation of different tunneling mechanisms at a level of device engineering.

关键词： carbide tunneling defect

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Field induced Chern insulating states in twisted monolayer–bilayer graphene

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Chinese Physics B 2024年第6期33卷 69-73页

作者：王政文韩英卓 Kenji Watanabe takashi taniguchi 姜宇航毛金海 School of Physical Science and CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100049China College of Materials Science and Optoelectronic Technology Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of SciencesBeijing 100049China Advanced Materials Laboratory National Institute for Materials ScienceTsukuba 305-0044Japan

Unraveling the mechanism underlying topological phases, notably the Chern insulators(Ch Is) in strong correlated systems at the microscopy scale, has captivated significant research interest. Nonetheless, Ch Is harboring topological information have not always manifested themselves, owing to the constraints imposed by displacement fields in certain experimental configurations. In this study, we employ density-tuned scanning tunneling microscopy(DT-STM) to investigate the Ch Is in twisted monolayer–bilayer graphene(t MBG). At zero magnetic field, we observe correlated metallic *** under a magnetic field, a metal–insulator transition happens and an integer Ch I is formed emanating from the filling index s = 3 with a Chern number C = 1. Our results underscore the pivotal role of magnetic fields as a powerful probe for elucidating topological phases in twisted Van der Waals heterostructures.

关键词： Chern insulators strong correlation effects two-dimensional van der Waals heterostructure density-tuned scanning tunneling microscopy(DT-STM)

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Oscillating paramagnetic Meissner effect and Berezinskii-Kosterlitz-Thouless transition in underdoped Bi2Sr2CaCu2O8+δ

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National Science Review 2024年第5期11卷 142-152页

作者： Shiyuan Wang Yijun Yu Jinxiang Hao Keyi Liang Bingke Xiang Jinjiang Zhu Yishi Lin Yinping Pan Genda Gu Kenji Watanabe takashi taniguchi Yang Qi Yuanbo Zhang Yihua Wang State Key Laboratory of Surface Physics and Department of Physics Fudan University Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Research Center for Functional Materials National Institute for Materials Science International Center for Materials Nanoarchitectonics National Institute for Materials Science Shanghai Research Center for Quantum Sciences

Superconducting phase transitions in two dimensions lie beyond the description of the Ginzburg-Landau symmetry-breaking paradigm for three-dimensional *** are Berezinskii-KosterlitzThouless（BKT） transitions of paired-electron condensate driven by the unbinding of topological excitations,*** recently discovered monolayers of layered high-transition-temperature（TC）cuprate superconductor Bi2Sr2CaCu2O8+δ（Bi2212） meant that this 2D superconductor promised to be ideal for the study of unconventional *** inhomogeneity posed challenges for distinguishing BKT physics from charge correlations in this ***,we utilize the phase sensitivity of scanning superconducting quantum interference device microscopy susceptometry to image the local magnetic response of underdoped Bi2212 from the monolayer to the bulk throughout its phase *** monolayer segregates into domains with independent phases at elevated temperatures below *** a single domain,we find that the susceptibility oscillates with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up to *** finite modulation period,as well as the broadening of the peaks when approaching Tc from below,suggests well-defined vortices that are increasingly screened by the dissociation of vortex-antivortex plasma through a BKT *** the multilayers,the susceptibility oscillation differs in a small temperature regime below TC,consistent with a dimensional crossover led by interlayer *** as strong evidence for BKT transition in the bulk,we observe a sharp jump in phase stiffness and paramagnetism at small fields just below *** results unify the superconducting phase transitions from the monolayer to the bulk underdoped Bi2212,and can be collectively referred to as the BKT transition with interlayer coupling.

关键词： cuprate superconductor monolayer Berezinskii-Kosterlitz-Thouless transition scanning SQUID paramagnetic Meissner effect

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Impact of device resistances in the performance of graphene-based terahertz photodetectors

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Frontiers of Optoelectronics 2024年第2期 89-99页

作者： óscar Castelló Sofía M.López Baptista Kenji Watanabe takashi taniguchi Enrique Diez Jesús Enrique Velázquez-Pérez Yahya M.Meziani José M.Caridad Juan A.Delgado-Notario Department of Applied Physics University of Salamanca Unidad de Excelencia en Luz y Materia Estructurada(LUMES) University of Salamanca Research Center for Electronic and Optical Materials National Institute for Materials Science Research Center for Materials Nanoarchitectonics National Institute for Materials Science Nanotechnology Group USAL–Nanolab University of Salamanca

In recent years, graphene field-effect-transistors(GFETs) have demonstrated an outstanding potential for terahertz(THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune(decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors.

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仗剑斩龙的诗人们——中唐诗歌中的龙神与祭祀

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南京师范大学文学院学报 2024年第1期 144-166页

作者：谷口高志陈文辉(译) 日本佐贺大学教育系佐贺县佐贺8408502 吉林外国语大学国际传媒学院吉林长春130117

随着佛教的渗透,在唐代,特别是中唐前后“河伯”被龙神代替,民间的龙神祭祀开始出现在诗文作品中,但其祭祀被定位为“淫祀”的一种。白居易和韩愈在《黑潭龙》《题炭谷湫祠堂》中将龙神的淫祀问题与奸臣、天子权威问题相关联,从中能够... 详细信息

随着佛教的渗透,在唐代,特别是中唐前后“河伯”被龙神代替,民间的龙神祭祀开始出现在诗文作品中,但其祭祀被定位为“淫祀”的一种。白居易和韩愈在《黑潭龙》《题炭谷湫祠堂》中将龙神的淫祀问题与奸臣、天子权威问题相关联,从中能够看出中唐时期诗人们的危机感和问题意识。而从盛唐到中唐,“代表国家安宁的龙”的象征性的崩坍,在杜甫的《奉同郭给事汤东灵湫作》诗作中可以看到。中唐时期洞庭湖水域作为非祭祀对象的恶龙等妖物的栖息地,频繁地出现在士人们的诗文中。水界的混乱,成为士人们心中世界秩序混乱的类比,进而与现实中的奸臣、朝廷权威问题相重合,激发了诗人们“斩龙”“驱龙”的愿望。概而言之,中唐时期诗人们出于自己官僚身份的自我认知以及对朝廷、世界的责任感和自负心,对危及朝廷的淫祀、恶龙等的存在产生了危机感和焦躁感,这种问题意识促使他们将其表现在了诗文作品中。

关键词：龙神祭祀淫祀白居易韩愈

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Optoelectronic properties of bottom gate-defined in-plane monolayer WSe_2 p–n junction

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Chinese Physics B 2018年第8期27卷 476-481页

作者： Di Liu Xiao-Zhuo Qi takashi taniguchi Xi-Feng Ren Guo-Ping Guo Key Laboratory of Quantum Information University of Science and Technology of ChinaChinese Academy of SciencesHefei 230026China Synergetic Innovation Center of Quantum Information&Quantum Physics University of Science and Technology of ChinaHefei 230026China National Institute for Materials Science Namiki 1-1Ibaraki 305-0044Japan

Monolayer transition-metal dichalcogenides （TMDs） are considered to be fantastic building blocks for a wide variety of optical and optoelectronic devices such as sensors, photodetectors, and quantum emitters, owing to their direct band gap, transparency, and mechanical flexibility. The core element of many conventional electronic and optoelectronic devices is the p-n junction, in which the p- and n-types of the semiconductor are formed by chemical doping in different regions. Here, we report a series of optoelectronic studies on a monolayer WSe2 in-plane p-n photodetector, demonstrating a low- power dissipation by showing an ambipolar behavior with a reduced threshold voltage by a factor of two compared with the previous results on a lateral electrostatically doped WSe2 p-n junction. The fabrication of the device is based on a polycarbonates （PC） transfer technique and hence no electron-beam exposure induced damage to the monolayer WSe2 is expected. Upon optical excitation, the photodetector demonstrates a photoresponsivity of 0.12 mA.W-1 and a maximum external quantum efficiency of 0.03%. Our study provides an alternative platform for a flexible and transparent two- dimensional photodetector, from which we expect to further promote the development of next-generation optoelectronic devices.

关键词： WSe2, photodetector transfer technique p-n junction

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Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors

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Chinese Physics Letters 2017年第4期34卷 87-91页

作者： Shi-Li Yan Zhi-Jian Xie Jian-Hao Chen takashi taniguchi Kenji Watanabe International Center for Quantum Materials Peking University Beijing 100871 High Pressure Group National Institute for Materials Science 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan Collaborative Innovation Center of Quantum Matter Beijing 100871

The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus （BP） by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10 V/nm to 0.83 V/nm. Our results suggest appealing potential for few-layer BP as a tunable bandgap material in infrared optoelectronies, thermoelectric power generation and thermal imaging.

关键词： Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors FET BP

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Superlubricity enabled dry transfer of non-encapsulated graphene

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Chinese Physics B 2019年第2期28卷 434-438页

作者： Zhe Ying Aolin Deng Bosai Lyu Lele Wang takashi taniguchi Kenji Watanabe Zhiwen Shi Key Laboratory of Artificial Structures and Quantum Control(Ministry of Education) School of Physics and AstronomyShanghai Jiao Tong University Collaborative Innovation Center of Advanced Microstructures National Institute for Materials Science

Transferring high-quality exfoliated graphene flakes onto different substrates while keeping the graphene free of polymer residues is of great importance, but at the same time very challenging. Currently, the only feasible way is the so-called all-dry "pick-and-lift" method, in which a hexagonal boron nitride(hBN) flake is employed to serve as a stamp to pick up graphene from one substrate and to lift it down onto another substrate. The transferred graphene samples, however,are always covered or encapsulated by hBN flakes, which leads to difficulties in further characterizations. Here, we report an improved "pick-and-lift" method, which allows ultra-clean graphene flakes to be transferred onto a variety of substrates without hBN coverage. Basically, by exploiting the superlubricity at the graphene/hBN stack interface, we are able to remove the top-layer hBN stamp by applying a tangential force and expose the underneath graphene.

关键词： superlubricity transfer graphene heterostructures

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Deterministic and replaceable transfer of silver flakes for microcavities

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Frontiers of physics 2023年第3期18卷 139-146页

作者： Tingting Wang Zhihao Zang Yuchen Gao Kenji Watanabe takashi taniguchi Wei Bao Yu Ye State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Research Center for Functional Materials National Institute for Materials Science1-1 NamikiTsukuba305-0044Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science1-1 NamikiTsukuba305-0044Japan Electrical&Computer Engineering University of Nebraska-LincolnLincolnNE 68588USA Yangtze Delta Institute of Optoelectronics Peking UniversityNantong 226010China

How to fabricate high-quality microcavities simply and at low cost without causing damage to environmentally sensitive active layers such as perovskites are crucial for the studies of exciton–polaritons,however,it remains challenging in the field of microcavity ***,once the top mirror is deposited,the detuning of the microcavity is fixed and there is no easy way to tune ***,we have developed a method for deterministically transferring silver mirrors,which is relatively simple and guarantees the active layer from damaging of high temperature,particle bombardment,etc.,during the deposition of the top ***,with the help of a glass probe,we demonstrate a replaceable silver transfer method to tune the detuning of the microcavity,thereby changing the coupling of photons and excitons *** developed deterministic and replaceable silver mirror transfer methods will provide the capability to fabricate high-quality and tunable microcavities and play an active role in the development of the exciton–polariton field.

关键词： silver microcavity transfer perovskite

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Electron-hole hybridization in bilayer graphene

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National Science Review 2020年第2期7卷 248-253页

作者： Siqi Wang Mervin Zhao Changjian Zhang Sui Yang Yuan Wang Kenji Watanabe takashi taniguchi James Hone Xiang Zhang NSF Nanoscale Science and Engineering Center (NSEC) University of California Materials Sciences Division Lawrence Berkeley National Laboratory Department of Mechanical Engineering Columbia University National Institute for Materials Science Faculties of Sciences and Engineering University of Hong Kong

Band structure determines the motion of electrons in a solid, giving rise to exotic phenomena when properly engineered. Drawing an analogy between electrons and photons, artificially designed optical lattices indicate the possibility of a similar band modulation effect in graphene systems. Yet due to the fermionic nature of electrons, modulated electronic systems promise far richer categories of behaviors than those found in optical lattices. Here, we uncovered a strong modulation of electronic states in bilayer graphene subject to periodic potentials. We observed for the first time the hybridization of electron and hole sub-bands, resulting in local band gaps at both primary and secondary charge neutrality points. Such hybridization leads to the formation of flat bands, enabling the study of correlated effects in graphene systems. This work may provide a novel way to manipulate electronic states in layered systems, which is important to both fundamental research and application.

关键词： band modulation periodic potential bilayer graphene

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