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
Multidisciplinary Sciences
Andreij C. Gadelha, Douglas A. A. Ohlberg, Cassiano Rabelo, Eliel G. S. Neto, Thiago L. Vasconcelos, Joao L. Campos, Jessica S. Lemos, Vinicius Ornelas, Daniel Miranda, Rafael Nadas, Fabiano C. Santana, Kenji Watanabe, Takashi Taniguchi, Benoit van Troeye, Michael Lamparski, Vincent Meunier, Viet-Hung Nguyen, Dawid Paszko, Jean-Christophe Charlier, Leonardo C. Campos, Luiz G. Cancado, Gilberto Medeiros-Ribeiro, Ado Jorio
Summary: The twisted bilayer graphene undergoes self-organized lattice reconstruction, resulting in the formation of a superlattice that modulates vibrational and electronic structures, leading to phenomena such as strong correlations and superconductivity. Although experimental techniques and theoretical models face challenges in observing and describing these effects, nano-Raman spectroscopy can localize some vibrational modes and provide insights into the effects of electron-phonon coupling on the material properties.
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, Physical
Wenxiang Liu, Yang Hong, Jingchao Zhang, Yanan Yue
Summary: This study comprehensively investigates the anisotropic thermal conductivity of twisted bilayer graphene (TBLG), revealing a strong non-monotonic correlation between thermal conductivity and twisting angles. The physical mechanism behind the decreasing thermal conductivity with increasing twisting angles is explained. The reported anisotropic thermal conductivity is important for thermal modulation and provides a valuable complement to phonon studies of TBLG.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
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
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
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
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
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
Materials Science, Multidisciplinary
Himani Arora, Zahra Fekri, Yagnika Nandlal Vekariya, Phanish Chava, Kenji Watanabe, Takashi Taniguchi, Manfred Helm, Artur Erbe
Summary: In this study, a fully-encapsulated BP-based field-effect transistor (FET) scheme is employed using a lithography-free via-encapsulation method. The electrical properties of the via-encapsulated BP FETs are found to be significantly improved compared to unencapsulated devices. The results demonstrate that the via-contacting scheme leads to superior performance in terms of higher mobility, lower hysteresis, and long-term ambient stability in BP FETs.
ADVANCED MATERIALS TECHNOLOGIES
(2023)
Article
Materials Science, Multidisciplinary
Yong Hyeon Kim, Sungyu Park, Chang Il Kwon, So Young Kim, Kenji Watanabe, Takashi Taniguchi, Jun Sung Kim
Summary: We studied the electrical transport properties of optimally Li+-intercalated FeSe nanoflakes. Using solid electrolyte gating, we achieved high and uniform electron doping of up to -0.55 electrons per Fe site in the FeSe nanoflakes, which exhibit a sharp superconducting transition at Tc -45.0 K. The temperature and magnetic-field dependent current-voltage characteristics revealed the two-dimensional nature of superconductivity in the intercalated FeSe nanoflakes. Self-field critical current measurements showed two distinct isotropic superconducting gaps with different gap ratios, suggesting the presence of two interband pairing channels in the highly electron-doped FeSe.
CURRENT APPLIED PHYSICS
(2023)
Article
Chemistry, Physical
Cheng Shen, Patrick J. Ledwith, Kenji Watanabe, Takashi Taniguchi, Eslam Khalaf, Ashvin Vishwanath, Dmitri K. Efetov
Summary: Magic-angle twisted trilayer graphene (MATTG) has flat electronic bands and exhibits correlated quantum phases. A spectroscopy technique is demonstrated in this work to dissociate intertwined bands and quantify the energy gaps and Chern numbers C of the correlated states in MATTG. Hard correlated gaps with C = 0 at integer moiré unit cell fillings and charge density wave states originating from van Hove singularities at fractional fillings are uncovered. Displacement-field-driven first-order phase transitions at charge neutrality and v = 2 are also demonstrated. Overall, these properties establish a diverse electrically tunable phase diagram of MATTG.
Article
Chemistry, Multidisciplinary
Yih-Ren Chang, Ryo Nanae, Satsuki Kitamura, Tomonori Nishimura, Haonan Wang, Yubei Xiang, Keisuke Shinokita, Kazunari Matsuda, Takashi Taniguchi, Kenji Watanabe, Kosuke Nagashio
Summary: The non-centrosymmetric layer stacking of SnS crystals grown on a van der Waals substrate is achieved by physical vapor deposition, and the shift current of SnS is demonstrated through polarization angle dependence and circular photogalvanic effect. The presence of 180 degrees ferroelectric domains in SnS is confirmed by multiple techniques, and an atomic model of the ferroelectric domain boundary is proposed. The direct observation of shift current and ferroelectric domains opens up new possibilities for future studies on shift-current photovoltaics.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Physical
Tyler James, Jonathan Bradford, James Kerfoot, Vladimir V. Korolkov, Manal Alkhamisi, Takashi Taniguchi, Kenji Watanabe, Anton S. Nizovtsev, Elisa Antolin, Elena Besley, Simon A. Svatek, Peter H. Beton
Summary: Monolayers of H2Pc are grown on hBN flakes and integrated into a van der Waals tunnel diode. Tunnel current generates photon emission close to the peaks observed in photoluminescence, and the electroluminescence suggests a multi-electron excitation pathway. The study provides insights into the excitation and relaxation of molecules in supramolecular monolayers and bulk crystals, as well as the role of energy level alignment in the emission process.
Article
Chemistry, Multidisciplinary
Koloman Wagner, Zakhar A. Iakovlev, Jonas D. Ziegler, Marzia Cuccu, Takashi Taniguchi, Kenji Watanabe, Mikhail M. Glazov, Alexey Chernikov
Summary: This study demonstrates the diffusion of excitons in a monolayer semiconductor with a continuously tunable Fermi sea of free charge carriers. The light emission from tightly bound exciton states in electrically gated WSe2 monolayer is detected using microscopy. The measurements reveal a nonmonotonic dependence of the exciton diffusion coefficient on the charge carrier density.
Article
Chemistry, Physical
Xi Wang, Xiaowei Zhang, Jiayi Zhu, Heonjoon Park, Yingqi Wang, Chong Wang, William G. Holtzmann, Takashi Taniguchi, Kenji Watanabe, Jiaqiang Yan, Daniel R. Gamelin, Wang Yao, Di Xiao, Ting Cao, Xiaodong Xu
Summary: The authors report the emergence of intercell moire exciton complexes in H-stacked WS2/WSe2 heterobilayers, where the exciton's hole from the WSe2 layer is surrounded by its bound electron's wavefunction distributed among three adjacent moire traps in the WS2 layer exhibiting an out-of-plane dipole and in-plane quadrupole. This work provides insights into and possibilities for engineering emergent exciton many-body states in correlated moire charge orders.
Article
Multidisciplinary Sciences
Canxun Zhang, Tiancong Zhu, Tomohiro Soejima, Salman Kahn, Kenji Watanabe, Takashi Taniguchi, Alex Zettl, Feng Wang, Michael P. P. Zaletel, Michael F. F. Crommie
Summary: In recent years, various phenomena such as correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have been observed in moire heterostructures. However, the lack of local electronic structure data has hindered the understanding of the underlying physical mechanisms. In this study, scanning tunnelling microscopy and spectroscopy are used to investigate the behaviour of electron-doped twisted monolayer-bilayer graphene, revealing the interplay between correlation, topology, and local atomic structure. The results provide insights into the gate-controlled quantum anomalous Hall insulator state in twisted moire heterostructures.
NATURE COMMUNICATIONS
(2023)
Article
Chemistry, Multidisciplinary
Soyun Kim, Dohun Kim, Kenji Watanabe, Takashi Taniguchi, Jurgen H. Smet, Youngwook Kim
Summary: The authors study integer and fractional quantum Hall states in a stack of two twisted Bernal bilayer graphene sheets. They suppress single-particle tunneling between the bilayers and benefit from strong interlayer Coulombic interactions. A Bose-Einstein condensate is observed for half-filling in each bilayer sheet, but only at orbital index 1. The energy of skyrmion/anti-skyrmion pair excitations is tentatively linked to this discrepancy.
Article
Chemistry, Multidisciplinary
Hyun-Soo Ra, Tae Wook Kim, Derrick Allan Taylor, Je-Jun Lee, Seungho Song, Jongtae Ahn, Jisu Jang, Takashi Taniguchi, Kenji Watanabe, Jae Won Shim, Jong-Soo Lee, Do Kyung Hwang
Summary: A 2D-0D hybrid optical multi-level memory (OMM) device operated by laser pulses is demonstrated using CdSe/ZnS type-I core/shell quantum dots. The study establishes the mechanism of the OMM effect and tests it by stimulating different positions on the hybrid structure with laser pulses. A fully optically-controlled multi-level memory inverter is proposed based on the independent MM characteristics induced by laser pulses.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Harshvardhan Jog, Luminita Harnagea, Dibyata Rout, Takashi Taniguchi, Kenji Watanabe, Eugene J. Mele, Ritesh Agarwal
Summary: We investigate the symmetries of 1T-TiSe2 and observe that the ground state of the CDW phase is achiral, but it can be transformed into a non-equilibrium chiral phase under high-intensity laser excitation, altering the electronic correlations in the material. The photogalvanic technique demonstrates the sensitivity to structural symmetries and provides evidence of different optically driven phases in 1T-TiSe2.
Article
Multidisciplinary Sciences
Tonghang Han, Zhengguang Lu, Giovanni Scuri, Jiho Sung, Jue Wang, Tianyi Han, Kenji Watanabe, Takashi Taniguchi, Liang Fu, Hongkun Park, Long Ju
Summary: The orbital multiferroicity in pentalayer rhombohedral graphene is demonstrated by low-temperature magneto-transport measurements, suggesting the possibility of electrically tunable ultralow-power valleytronic and magnetic devices.
Article
Materials Science, Multidisciplinary
Donghai Li, Hangyong Shan, Heiko Knopf, Kenji Watanabe, Takashi Taniguchi, Ying Qin, Sefaattin Tongay, Falk Eilenberger, Sven Hoefling, Christian Schneider, Tobias Brixner
Summary: In this study, coherent 2D photoluminescence-detected micro-spectroscopy was used to detect oscillating 2D peaks exclusively from a spatial trap. The observed variation of oscillatory phases suggests the existence of a coupling between the discretized polariton modes, accompanied by the generation of coherent phonons.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Materials Science, Multidisciplinary
E. Monch, S. O. Potashin, K. Lindner, I. Yahniuk, L. E. Golub, V. Yu. Kachorovskii, V. V. Bel'kov, R. Huber, K. Watanabe, T. Taniguchi, J. Eroms, D. Weiss, S. D. Ganichev
Summary: We present a study on the conversion of terahertz radiation into a dc current in spatially modulated bilayer graphene, tunable by magnetic field and gate voltage. We observe a sharp cyclotron resonance in the photocurrent and discover two effects caused by electron-electron interaction: the splitting of the resonance due to Coulomb coupling and the suppression of its second harmonic due to interparticle collisions. A theoretical model that fits the experimental data perfectly is developed, suggesting that the ratchet current is generated in the hydrodynamic regime of nonideal electron liquid.
Article
Nanoscience & Nanotechnology
Cheol-Yeon Cheon, Zhe Sun, Jiang Cao, Juan Francisco Gonzalez Marin, Mukesh Tripathi, Kenji Watanabe, Takashi Taniguchi, Mathieu Luisier, Andras Kis
Summary: This study demonstrates the bulk photovoltaic effect in centrosymmetric PtSe2 material by breaking the inversion symmetry through structural disorder. The results show that defects in the material can induce photovoltaic functionality, thus expanding the range of materials suitable for light sensing and energy-harvesting applications.
NPJ 2D MATERIALS AND APPLICATIONS
(2023)
