Article
Chemistry, Multidisciplinary
Shan Liu, Baizhe He, Wei Yang, Xiahong Zhou, Xudong Xue, Mengya Liu, Yao Zhao, Xinhe Wang, Jia Si, Fuyi Wang, Zhiyong Zhang, Lianmao Peng, Gui Yu
Summary: This study reports the use of local space-confined chemical vapor deposition growth technique to efficiently produce high-quality single-crystal twisted bilayer graphene (TBG) with twist angles ranging from 0 to 30 degrees on liquid copper substrates. The clean surface, high crystallinity, thermal stability, stacking structure, growth mechanism, and electrical transport properties of the as-grown TBG are investigated. The results show that the liquid copper surface promotes the growth of TBG with twist-angle-dependent electronic properties.
ADVANCED MATERIALS
(2023)
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.
Editorial Material
Nanoscience & Nanotechnology
Tatiana Latychevskaia
Summary: The topological parameters of the channel network in twisted bilayer graphene can be manipulated by intercalating lithium atoms.
NATURE NANOTECHNOLOGY
(2023)
Article
Chemistry, Physical
Weiyi Lin, Pingping Zhuang
Summary: This study investigates the charge distribution in bilayer graphene and reveals that the hole distribution in the top and bottom layers of AB-BLG and t-BLG are similar, with the additional layer reducing the charge exchange at the graphene/dopant interface.
APPLIED SURFACE SCIENCE
(2022)
Article
Multidisciplinary Sciences
Joe Finney, Aaron L. Sharpe, Eli J. Fox, Connie L. Hsueh, Daniel E. Parker, Matthew Yankowitz, Shaowen Chen, Kenji Watanabe, Takashi Taniguchi, Cory R. Dean, Ashvin Vishwanath, M. A. Kastner, David Goldhaber-Gordon
Summary: We present transport measurements of bilayer graphene with a 1.38 degrees interlayer twist. Although we do not observe correlated insulating states or band reorganization, we do observe several highly unusual behaviors in magnetotransport, including large and quadratic magnetoresistance for a large range of densities around half filling of the moire bands, as well as the splitting and bending of magnetoresistance minima corresponding to gaps between Landau levels as a function of density and field. These features appear to be a generic class of experimental manifestations of Hofstadter's butterfly and may provide insight into the emergent states of twisted bilayer graphene.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Multidisciplinary Sciences
Yu Saito, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Takashi Taniguchi, Kenji Watanabe, J. I. A. Li, Erez Berg, Andrea F. Young
Summary: The study explores the finite-temperature dynamics of spin and valley isospins in magic-angle twisted bilayer graphene, revealing a resistivity peak at high temperatures near a superlattice filling factor of -1, suggesting a Pomeranchuk-type mechanism. The data indicate the presence of a finite-field magnetic phase transition and a small isospin stiffness in the system.
Article
Chemistry, Physical
Ningning Xuan, Aozhen Xie, Bing Liu, Zhengzong Sun
Summary: Bilayer graphene (BLG) has attracted significant research interest for its tunable physical properties dependent on twisted angles and interlayer interaction. This article focuses on the study of BLG single crystals with representative twisted angles of approximately 0 degrees and approximately 30 degrees, grown by chemical vapor deposition (CVD). The surface potentials of pristine BLG single crystals indicate that the surface potential difference between single layer graphene (SLG) and BLG is lower for approximately 0 degrees compared to approximately 30 degrees. Additionally, reversible tuning of the electrical coupling and properties of BLG is achieved through diazonium salts reaction and nitrogen doping, resulting in a wide range of surface potential tuning from 0 to 50 mV.
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
Chemistry, Multidisciplinary
Shuichi Iwakiri, Folkert K. de Vries, Elias Portoles, Giulia Zheng, Takashi Taniguchi, Kenji Watanabe, Thomas Ihn, Klaus Ensslin
Summary: In this study, we have successfully implemented an electron interferometer controlled purely by electrostatic gating in encapsulated bilayer graphene. The device demonstrates a coherence length of many microns and seamless tunability of Aharonov-Bohm oscillations and carrier types. The gate-defined ring geometry also has the potential to explore correlated quantum states in twisted bilayer graphene interferometers.
Article
Chemistry, Physical
Wei Wei, Chi Zhang, Haobo Li, Jiaqi Pan, Zhen Tan, Yajuan Li, Yi Cui
Summary: In this study, the layer stacking structures and film uniformity of large-area uniform bilayer graphene (BLG) were successfully controlled through a two-step carbon segregation method. Using real-time surface imaging and thermodynamics-limit process, the growth of extremely uniform 15 degrees-twisted BLG and AB-stacked BLG were achieved at specific temperatures.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
Article
Chemistry, Physical
Wei Wei, Chi Zhang, Haobo Li, Jiaqi Pan, Zhen Tan, Yajuan Li, Yi Cui
Summary: In this study, large-area uniform bilayer graphene (BLG) with different twisted angles was synthesized by controlling film uniformity and stacking structures through a two-step carbon segregation method. The growth dynamics were manipulated to achieve different stacking structures at varied temperatures.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
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
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
Multidisciplinary Sciences
Yiran Zhang, Robert Polski, Alex Thomson, Etienne Lantagne-Hurtubise, Cyprian Lewandowski, Haoxin Zhou, Kenji Watanabe, Takashi Taniguchi, Jason Alicea, Stevan Nadj-Perge
Summary: A study finds that placing monolayer tungsten diselenide (WSe2) on bilayer graphene can enhance Cooper pairing and increase the critical temperature of superconductivity. The superconducting state exhibits polarized spin-valley flavors and occurs only under perpendicular electric fields that push graphene hole wavefunctions towards WSe2, indicating a key role of proximity-induced (Ising) spin-orbit coupling. These results pave the way for engineering robust, highly tunable, and ultra-clean graphene-based superconductors.
Article
Engineering, Mechanical
Tawfiqur Rakib, Pascal Pochet, Elif Ertekin, Harley T. Johnson
Summary: We observe a helical dislocation network accompanied by large out-of-plane deformation in twisted bilayer graphene (tBLG). By atomistic calculations, we demonstrate two distinct out-of-plane deformation modes, a breathing mode with small deformation and a bending mode with significantly larger corrugation. The out-of-plane deformation is caused by inhomogeneous interlayer coupling resulting from the periodic stacking order of the tBLG moire superlattice.
EXTREME MECHANICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Yue Luo, Nannan Mao, Dapeng Ding, Ming-Hui Chiu, Xiang Ji, Kenji Watanabe, Takashi Taniguchi, Vincent Tung, Hongkun Park, Philip Kim, Jing Kong, William L. Wilson
Summary: In-plane anisotropic exciton-polariton propagation in SnSe allows for nanoscale imaging of in-plane ferroelectric domains. The control and manipulation of exciton-polaritons in two-dimensional quantum materials has the potential for nanoscale control of electromagnetic fields. By studying the propagation dynamics and dispersion of exciton-polaritons in SnSe, a group-IV monochalcogenide semiconductor, it was found that this propagation enables imaging of the in-plane ferroelectric domains. Additionally, electric switching of exciton-polaritons in the ferroelectric domains of this complex van der Waals system was demonstrated, suggesting the potential for reconfigurable polaritonic optical devices.
NATURE NANOTECHNOLOGY
(2023)
Article
Chemistry, Multidisciplinary
Yueshen Wu, Yuxiong Hu, Cong Wang, Xiang Zhou, Xiaofei Hou, Wei Xia, Yiwen Zhang, Jinghui Wang, Yifan Ding, Jiadian He, Peng Dong, Song Bao, Jinsheng Wen, Yanfeng Guo, Kenji Watanabe, Takashi Taniguchi, Wei Ji, Zhu-Jun Wang, Jun Li
Summary: This study examines the atomic structure of Fe3GeTe2 crystals with varying Curie temperature (T-c) values. It is found that high-T-c samples (210 and 230 K) have Fe-intercalation within the van der Waals gap, which leads to an exchange bias effect observed in electrical transport measurements. The absence of Fe intercalation or bias effect in low-T-c samples (160 K) is also noted. First-principles calculations suggest that the Fe-intercalation layer contributes to the local antiferromagnetic coupling and enhancement of T-c through interlayer exchange paths.
ADVANCED MATERIALS
(2023)
Article
Physics, Applied
Sourav Paul, M. B. Abhijith, Prasenjit Ghosh, Prajna Paromita Chanda, Nicholas R. R. Glavin, Ajit K. K. Roy, Kenji Watanabe, Takashi Taniguchi, Vidya Kochat
Summary: Twisted 2D bilayers of van der Waals materials show promising advances in nanoelectronics and photonics. Raman spectroscopy is used to probe the stacking order and interlayer interactions of bilayer WSe2 at different twist angles. This characterization technique offers insight into the optoelectronic properties of 2D materials and heterostructures.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Josep Ingla-Aynes, Antonio L. R. Manesco, Talieh S. S. Ghiasi, Serhii Volosheniuk, Kenji Watanabe, Takashi Taniguchi, Herre S. J. van der Zant
Summary: We conducted multiterminal measurements in a ballistic bilayer graphene channel and defined multiple spin- and valley-degenerate quantum point contacts (QPCs) using electrostatic gating. By patterning QPCs of different shapes along different crystallographic directions, we investigated the impact of size quantization and trigonal warping on transverse electron focusing (TEF). Our TEF spectra showed eight distinct peaks with similar amplitudes, indicating specular reflections at the gate-defined edges and phase-coherent transport. Despite small gate-induced bandgaps in our sample (less than or equal to 45 meV), several peaks were observable up to 100 K, demonstrating the potential for ballistic interconnects in valleytronic devices.
Article
Chemistry, Multidisciplinary
Ayelet Zalic, Takashi Taniguchi, Kenji Watanabe, Snir Gazit, Hadar Steinberg
Summary: In this work, a novel atomically thin, all van der Waals SQUID is constructed, in which current flows between NbSe2 contacts through parallel graphene weak links. The 2D planar SQUID remains stable at high in-plane fields, enabling the tracing of critical current interference patterns and the observation of a field-driven transition. The asymmetric SQUID geometry is further suggested for directly probing current density in the absence of phase information.
Article
Physics, Condensed Matter
Dominique Ausserre, Refahi Abou Khachfe, Takashi Taniguchi, Kenji Watanabe, Fabien Vialla
Summary: The properties of two-dimensional material stacks depend on the number of monolayers present. Quantifying this number is challenging due to the heterogeneity of 2D stacks. Optical interferential techniques can visualize monolayer variations but require complex numerical models for determining monolayer counts. A self-calibrating method using backside absorbing layer microscopy is demonstrated to instantly count monolayers across the sample surface without the need for detailed parameters or the structure of the contrast-enhancing layer. The method is applied to hexagonal boron nitride stacks, achieving accurate monolayer counting up to 36 layers using basic image analysis.
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
(2023)
Article
Multidisciplinary Sciences
Roberto Rosati, Ioannis Paradisanos, Libai Huang, Ziyang Gan, Antony George, Kenji Watanabe, Takashi Taniguchi, Laurent Lombez, Pierre Renucci, Andrey Turchanin, Bernhard Urbaszek, Ermin Malic
Summary: In this study, the existence of bound charge transfer (CT) excitons at the interface of hBN-encapsulated lateral MoSe2-WSe2 heterostructures was investigated. The theoretical prediction was compared with experimental measurements, confirming the presence of low-energy CT excitons. These excitons exhibit small binding energies and large dipole moments, making them promising for optoelectronic applications.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Heejun Kim, Kumpei Aino, Keisuke Shinokita, Wenjin Zhang, Kenji Watanabe, Takashi Taniguchi, Kazunari Matsuda
Summary: By stacking two monolayers with slight lattice mismatches, a moire potential is created, which acts as periodic quantum confinement for optically generated excitons and provides 0D quantum systems. This study experimentally investigates the previously unknown structures and dynamics of moire exciton states in twisted MoSe2/WSe2 heterobilayers using photoluminescence spectroscopy. Phonon-mediated dark exciton states above bright exciton states are observed, and the dynamics of moire excitons are found to be influenced by radiative recombination processes at low temperatures and phonon-assisted non-radiative processes at high temperatures. Additional peaks at high energies under high-power excitation conditions indicate emission from triplet bright moire exciton states. The experimental evidence of bright and dark exciton states within the moire potential offers new platforms for quantum optics applications using moire superlattices.
ADVANCED OPTICAL MATERIALS
(2023)
Article
Physics, Applied
Domitille Gerard, Michael Rosticher, Kenji Watanabe, Takashi Taniguchi, Julien Barjon, Stephanie Buil, Jean-Pierre Hermier, Aymeric Delteil
Summary: Integrated quantum photonics relies on quantum emitters integrated into on-chip photonic circuits, and hexagonal boron nitride (hBN) is recognized as a compatible material due to its high refractive index and low losses. In this study, hBN waveguide nanofabrication is combined with local generation of quantum emitters to realize a fully top-down quantum photonic circuit in this material at room temperature. This proof of principle represents a significant step towards deterministic quantum photonic circuits in hBN.
APPLIED PHYSICS LETTERS
(2023)
Article
Chemistry, Multidisciplinary
Denis Yagodkin, Abhijeet Kumar, Elias Ankerhold, Johanna Richter, Kenji Watanabe, Takashi Taniguchi, Cornelius Gahl, Kirill I. Bolotin
Summary: Our study presents a time-resolved ultrafast photocurrent technique for probing the formation dynamics of optically dark excitons. We demonstrate its effectiveness by extracting the interlayer exciton formation time in a MoS2/MoSe2 heterostructure and showing its dependence on fluence. Additionally, this technique provides access to the dynamics of carriers and their interlayer transport.
Article
Multidisciplinary Sciences
Ciaran Mullan, Sergey Slizovskiy, Jun Yin, Ziwei Wang, Qian Yang, Shuigang Xu, Yaping Yang, Benjamin A. A. Piot, Sheng Hu, Takashi Taniguchi, Kenji Watanabe, Kostya S. S. Novoselov, A. K. Geim, Vladimir I. I. Falko, Artem Mishchenko
Summary: Van der Waals assembly allows for the design of electronic states in 2D materials by superimposing a long-wavelength periodic potential. This twistronics approach has led to various new physics phenomena and can also be applied to tune electronic states in 3D crystals.
Article
Multidisciplinary Sciences
Aviram Uri, Sergio C. de la Barrera, Mallika T. Randeria, Daniel Rodan-Legrain, Trithep Devakul, Philip J. D. Crowley, Nisarga Paul, Kenji Watanabe, Takashi Taniguchi, Ron Lifshitz, Liang Fu, Raymond C. Ashoori, Pablo Jarillo-Herrero
Summary: Researchers have created a highly tunable quasicrystal structure by twisting three layers of graphene and forming two mutually incommensurate moire patterns. This 'moire quasicrystal' allows for control over the electronic system between periodic and quasiperiodic regimes, and exhibits superconductivity and flavour-symmetry-breaking phase transitions.
Article
Nanoscience & Nanotechnology
Shi Guo, Savvas Germanis, Takashi Taniguchi, Kenji Watanabe, Freddie Withers, Isaac J. Luxmoore
Summary: In this work, a device geometry consisting of gold pillars embedded in a van der Waals heterostructure is presented. The gold pillars generate strain and inject charge carriers, enabling positional control and electrical pumping of a single photon emitter. Increasing the thickness of the hexagonal boron nitride tunnel barriers restrict electroluminescence but enable electrical control of the emission energy of the site-controlled single photon emitters, with measured energy shifts reaching 40 meV.
Article
Physics, Multidisciplinary
Michele Masseroni, Tingyu Qu, Takashi Taniguchi, Kenji Watanabe, Thomas Ihn, Klaus Ensslin
Summary: In this study, the insulating state of a dual-gated exfoliated bilayer MoS2 field-effect transistor was investigated through magnetotransport experiments. It was found that at low electron density (about 1.4 x 1012 cm-2) and a perpendicular magnetic field (7 Tesla), the resistance exceeded the zero field resistance by more than one order of magnitude and exponentially dropped with increasing temperature. The result suggests that the insulating state of MoS2 originates from a combination of disorder-driven electron localization and Coulomb interactions.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Materials Science, Multidisciplinary
Dipanjan Saha, Dacen Waters, Ching-Chen Yeh, Swapnil M. Mhatre, Ngoc Thanh Mai Tran, Heather M. Hill, Kenji Watanabe, Takashi Taniguchi, David B. Newell, Matthew Yankowitz, Albert F. Rigosi
Summary: This paper reports on the experimental demonstration of single-slit diffraction exhibited by electrons propagating in encapsulated graphene. Nanometer-scale device designs and predictive calculations were used to accurately describe the observed phenomenon. The exaggerated asymmetry between electrons and holes observed in this experiment opens up possibilities for building versatile diffraction switches.