Article
Chemistry, Multidisciplinary
Hongrun Zhang, Zhijian Shi, Zhicheng Jiang, Ming Yang, Jingwei Zhang, Ziyuan Meng, Tonghua Hu, Fucai Liu, Long Cheng, Yong Xie, Jincheng Zhuang, Haifeng Feng, Weichang Hao, Dawei Shen, Yi Du
Summary: This study reports the appearance of flat bands (FBs) in 2D geometrically frustrated systems caused by quantum destructive interference (QDI), providing experimental evidence of the complete electronic QDI induced FB contributed by the 2D breathing-kagome layers of Nb atoms in Nb3TeCl7 (NTC). It also establishes the tunable roles of the on-site energy over Nb sites on bandwidth, energy position, and topology of FBs in NTC, demonstrating the potential to manipulate FB characteristics in 4d transition-metal-based breathing-kagome materials.
ADVANCED MATERIALS
(2023)
Article
Physics, Multidisciplinary
Weijie Wang, Xiaolong Lu, Hang Xie
Summary: In this study, the non-perturbative Floquet method was used to investigate the photo-induced topological phase transitions and edge states properties of graphene nanoribbons under light irradiation of different frequencies. The study analyzed the Floquet energy bands of ribbon and bulk graphene to understand the cause of the phase transitions and their relation to edge states, and also discovered the impact of graphene nanoribbon size on band gap and edge states in the presence of light.
Article
Physics, Multidisciplinary
Albert F. Adiyatullin, Lavi K. Upreti, Corentin Lechevalier, Clement Evain, Francois Copie, Pierre Suret, Stephane Randoux, Pierre Delplace, Alberto Amo
Summary: By implementing a synthetic photonic lattice in a two-coupled ring system, we have successfully designed an anomalous Floquet metal that exhibits two different topological properties in its gapless bulk. Firstly, this synthetic lattice features bands characterized by a winding number, which emerges from the breakup of inversion symmetry and is directly linked to the appearance of Bloch suboscillations in its bulk. Secondly, the Floquet nature of the lattice leads to well-known anomalous insulating phases with topological edge states. The combination of broken inversion symmetry and periodic time modulation studied here enriches the range of topological phases available in lattices subject to Floquet driving, and suggests the potential emergence of novel phases when periodic modulation is combined with the breakup of spatial symmetries.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Multidisciplinary
Matheus I. N. Rosa, Massimo Ruzzene, Emil Prodan
Summary: Twisted bilayered systems exhibit higher dimensional topological phases and 4D integer quantum Hall effect, which can be accessed by sliding the layers relative to each other.
COMMUNICATIONS PHYSICS
(2021)
Article
Physics, Multidisciplinary
Zhengwang Cheng, Zhilong Hu, Shaojian Li, Xinguo Ma, Zhifeng Liu, Mei Wang, Jing He, Wei Zou, Fangsen Li, Zhiqiang Mao, Minghu Pan
Summary: The study investigates the band structure of the "square-net" topological material ZrGeS, revealing its unique electronic properties suitable for exploring Dirac-fermions related physics and applications of topological devising.
NEW JOURNAL OF PHYSICS
(2021)
Article
Mathematics, Interdisciplinary Applications
Boquan Ren, Yaroslav Kartashov, Hongguang Wang, Yongdong Li, Yiqi Zhang
Summary: Topological edge states can form in periodic materials with specific degeneracies in their modal spectra under the breaking of certain symmetries. Unconventional topological edge states can exist in Floquet insulators based on arrays of helical waveguides with hybrid edges, even if the hybrid edges are long. These edge states are topologically protected and persist in the presence of focusing nonlinearity of the material, expanding the variety of geometrical shapes in which topological insulators can be constructed.
CHAOS SOLITONS & FRACTALS
(2023)
Article
Multidisciplinary Sciences
Sunny Gupta, Henry Yu, Boris Yakobson
Summary: The authors propose a method to achieve tunable bandwidth in one-dimensional flat bands by stamping or growing a two-dimensional monolayer on a non-Euclidean topography-patterned surface. It is found that bi-periodic sinusoidal deformation can generate unexpected spatial dependence of pseudo-electric and magnetic fields, leading to anisotropic confinement and one-dimensional flat bands.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Multidisciplinary
Xu-Chuan Wu, Shen Xu, Jian-Feng Zhang, Huan Ma, Kai Liu, Tian-Long Xia, Shan-Cai Wang
Summary: This paper investigates the magnetoresistance origin of single crystal CaAl4 with C2/m structure at low temperature, revealing unsaturated magnetoresistance of around 3000% at 2.5 K and 14 T as the fingerprints of XMR materials. The study uses a combination of ARPES and first-principles calculations to elaborate on the multiband features and anisotropic Fermi surfaces, explaining the discrepancies in the isotropic two-band model. Despite a structural phase transition from I4/mmm to C2/m, the subtle impact on the electronic structure is revealed through ARPES measurements, highlighting CaAl4 as a new reference material for exploring the XMR phenomena.
Article
Chemistry, Multidisciplinary
Julian Maklar, Raul Stuehler, Maciej Dendzik, Tommaso Pincelli, Shuo Dong, Samuel Beaulieu, Alexander Neef, Gang Li, Martin Wolf, Ralph Ernstorfer, Ralph Claessen, Laurenz Rettig
Summary: In this study, the electron dynamics of the two-dimensional quantum spin Hall (QSH) candidate bismuthene were investigated using time- and angle-resolved photoemission spectroscopy. Shorter lifetimes of photocarriers in bismuthene compared to conventional semiconductors were observed, which can be attributed to the presence of topological in-gap states. This study marks a critical step toward optical control of QSH functionalities.
Article
Nanoscience & Nanotechnology
Xin Qiao, Luojia Wang, Guangzhen Li, Xianfeng Chen, Luqi Yuan
Summary: Synthetic frequency dimensions offer important opportunities for investigating novel topological phenomena. In this study, a Floquet SSH model with time-dependent hoppings is explored by ultrastrongly modulating ring resonators, leading to the separation of originally degenerate topological states and the emergence of a series of edge states with complex multi-frequency oscillations. This system with stronger modulations widens the bandgap, providing an effective way to localize pulses in synthetic frequency dimensions.
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
Multidisciplinary Sciences
Xiao-Xiao Zhang, Naoto Nagaosa
Summary: The nonequilibrium quantum dynamics of many-body systems is a cutting-edge field in condensed matter physics, and recent advancements in time-resolved spectroscopic techniques have revealed diverse phenomena. This study theoretically demonstrates that photoexcited surface states of genuine or magnetically doped topological insulators exhibit intriguing topological spin textures, resembling tornado-like patterns, in spin-resolved angle-resolved photoemission spectroscopy (ARPES). The origin of these patterns is revealed as a unique nonequilibrium photoinduced topological winding phenomenon. These findings not only provide significant tomography of important system information but also enable unique dichroic topological switchings of momentum-space spin textures.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Chemistry, Multidisciplinary
Kate Reidy, Paulina Ewa Majchrzak, Benedikt Haas, Joachim Dahl Thomsen, Andrea Konecna, Eugene Park, Julian Klein, Alfred J. H. Jones, Klara Volckaert, Deepnarayan Biswas, Matthew D. Watson, Cephise Cacho, Prineha Narang, Christoph T. Koch, Soren Ulstrup, Frances M. Ross, Juan Carlos Idrobo
Summary: The integration of metallic contacts with 2D semiconductors can significantly affect the local optoelectronic properties. In this study, we analyze the local excitonic changes in a 2D semiconductor MoS2 in contact with Au. Our findings suggest that the observed changes are due to the dielectric screening of the excitonic Coulomb interaction, and increasing the van der Waals distance can optimize excitonic spectra in mixed-dimensional interfaces.
Article
Multidisciplinary Sciences
Kritika Vijay, Durga Sankar Vavilapalli, Ashok Arya, S. K. Srivastava, Rashmi Singh, Archna Sagdeo, S. N. Jha, Kranti Kumar, Soma Banik
Summary: The idea of manipulating spins in magnetic two-dimensional van der Waal materials through strain has led to the development of new generation spintronic devices. Magneto-strain effects arise due to thermal fluctuations and magnetic interactions, influencing the lattice dynamics and electronic bands. In this study, the mechanism of magneto-strain effects in CrGeTe3, a vdW material, across the ferromagnetic transition is investigated. It is found that an isostructural transition occurs in CrGeTe3 with lattice modulation during the ferromagnetic ordering. The in-plane lattice contraction leads to magnetocrystalline anisotropy, while the electronic structure exhibits band shifts, broadening, and twinned bands in the ferromagnetic phase.
SCIENTIFIC REPORTS
(2023)
Article
Optics
Meng Li, Chu Li, Linyu Yan, Qiang Li, Qihuang Gong, Yan Li
Summary: This paper reports the experimental realization of fractal photonic anomalous Floquet topological insulators, in which a lattice composed of dual Sierpinski carpet is fabricated using femtosecond laser direct writing. The fabricated lattice supports multiple chiral edge states and enables efficient hopping of quantum states. The generation of highly indistinguishable single-photon chiral edge states in the fractal lattice suggests its potential applications in various quantum operations and encoding of quantum information.
LIGHT-SCIENCE & APPLICATIONS
(2023)
Article
Nanoscience & Nanotechnology
Joel Perez-Urquizo, Yanko Todorov, Lianhe Li, Alexander G. Davies, Edmund H. Linfield, Carlo Sirtori, Julien Madeo, Keshav M. Dani
Summary: Patch antenna arrays have a significant impact on modern telecommunications in the RF range, while there is a growing demand for similar monolithic platforms for terahertz emitters. The use of microcavities with precise control of emission through interconnections introduces advanced functionalities for polarization control and beam steering.
Article
Physics, Multidisciplinary
Fumiaki Miyamaru, Chihiro Mizuo, Toshihiro Nakanishi, Yosuke Nakata, Kakeru Hasebe, Shintaro Nagase, Yu Matsubara, Yusuke Goto, Joel Perez-Urquizo, Julien Madeo, Keshav M. Dani
Summary: The experimental demonstration involves observing frequency-shift dynamics at a temporal boundary in the terahertz (THz) region using a scheme that controls the structural dispersion of a metal-semiconductor waveguide. Ultrafast structural-dispersion switching is achieved within a subpicosecond timescale by illuminating the waveguide surface with an optical pump pulse during THz pulse propagation. The high conversion efficiency, up to 23%, allows for direct observation of rapid THz frequency variation around the temporal boundary.
PHYSICAL REVIEW LETTERS
(2021)
Review
Optics
Xing Zhu, David R. Bacon, Julien Madeo, Keshav M. Dani
Summary: This review focuses on single- to few-cycle terahertz generation in lithium niobate (LN), including the basic principles, techniques, latest developments, and limitations. Emphasis is placed on the tilted pulse front (TPF) technique, which has been shown to improve THz generation efficiency but still has many limitations. Different geometries used to produce continuous and discrete TPF are systematically discussed, and the advantages and limitations of current techniques as well as future trends are summarized.
Article
Nanoscience & Nanotechnology
Kyle Frohna, Miguel Anaya, Stuart Macpherson, Jooyoung Sung, Tiarnan A. S. Doherty, Yu-Hsien Chiang, Andrew J. Winchester, Kieran W. P. Orr, Julia E. Parker, Paul D. Quinn, Keshav M. Dani, Akshay Rao, Samuel D. Stranks
Summary: By combining quantitative optical spectroscopic techniques and synchrotron nanoprobe measurements, we can visualize the nanoscale chemical, structural, and optoelectronic landscape in halide perovskite devices. Compositional disorder plays a dominant role in the optoelectronic response, while the influence of nanoscale strain variations is weaker.
NATURE NANOTECHNOLOGY
(2022)
Article
Pharmacology & Pharmacy
Takashi Nakano, Shakila B. Rizwan, David M. A. Myint, Jason Gray, Sean M. Mackay, Paul Harris, Christopher G. Perk, Brian I. Hyland, Ruth Empson, Eng Wui Tan, Keshav M. Dani, John N. J. Reynolds, Jeffery R. Wickens
Summary: This study demonstrates a novel drug delivery system based on hollow-gold nanoparticles tethered to liposomes, which can release drugs in high concentration to inhibit neurons and suppress seizure activity when activated by optical or acoustic stimulation. The system allows precise temporal control over drug exposure.
Article
Chemistry, Multidisciplinary
Arka Karmakar, Abdullah Al-Mahboob, Christopher E. Petoukhoff, Oksana Kravchyna, Nicholas S. Chan, Takashi Taniguchi, Kenji Watanabe, Keshav M. Dani
Summary: This study shows that nonradiative energy transfer dominates over interlayer charge transfer in type-II heterostructures formed by transition metal dichalcogenides. It also demonstrates an innovative way to increase the photoluminescence intensity of desired materials by carefully choosing the right material combination.
Article
Multidisciplinary Sciences
Stuart Macpherson, Tiarnan A. S. Doherty, Andrew J. Winchester, Sofiia Kosar, Duncan N. Johnstone, Yu-Hsien Chiang, Krzysztof Galkowski, Miguel Anaya, Kyle Frohna, Affan N. Iqbal, Satyawan Nagane, Bart Roose, Zahra Andaji-Garmaroudi, Kieran W. P. Orr, Julia E. Parker, Paul A. Midgley, Keshav M. Dani, Samuel D. Stranks
Summary: Understanding the nanoscopic chemical and structural changes is crucial for mitigating device degradation in emerging energy materials. Researchers have developed a multimodal microscopy toolkit to investigate the impact of phase impurities on the performance and longevity of formamidinium-rich perovskite absorbers. The study also demonstrates that manipulating these impurities can alleviate performance losses and intrinsic degradation processes.
Article
Multidisciplinary Sciences
Ouri Karni, Elyse Barre, Vivek Pareek, Johnathan D. Georgaras, Michael K. L. Man, Chakradhar Sahoo, David R. Bacon, Xing Zhu, Henrique B. Ribeiro, Aidan L. O'Beirne, Jenny Hu, Abdullah Al-Mahboob, Mohamed M. M. Abdelrasoul, Nicholas S. Chan, Arka Karmakar, Andrew J. Winchester, Bumho Kim, Kenji Watanabe, Takashi Taniguchi, Katayun Barmak, Julien Madeo, Felipe H. da Jornada, Tony F. Heinz, Keshav M. Dani
Summary: Interlayer excitons, electron-hole pairs bound across atomically thin layered semiconductors, have attracted attention for quantum information applications. In this study, images of the time-resolved and momentum-resolved distribution of both particles were captured in a WSe2/MoS2 heterostructure, providing direct measurements of the interlayer exciton diameter and its localization. The results show that interlayer excitons can be highly localized within small moire unit cells.
News Item
Physics, Multidisciplinary
Julien Madeo, Keshav M. Dani
Summary: Quantum confinement effects provide a more comprehensive understanding of extreme optical nonlinearities in nano-engineered solids, offering a pathway to unlock the potential of high-order harmonic generation.
Article
Multidisciplinary Sciences
Valynn Katrine Mag-usara, Mary Clare Escano, Christopher E. Petoukhoff, Garik Torosyan, Laura Scheuer, Julien Madeo, Jessica Afalla, Miezel L. Talara, Joselito E. Muldera, Hideaki Kitahara, David R. Bacon, Makoto Nakajima, Keshav Dani, Evangelos Th. Papaioannou, Rene Beigang, Masahiko Tani
Summary: This study investigates the pump wavelength dependence of terahertz emission from an optimized Fe/Pt spintronic bilayer on MgO substrate. The results show the sensitivity of spintronic terahertz emission to both the optical absorptance of the heterostructure and the energy-dependent spin transport.
Proceedings Paper
Engineering, Electrical & Electronic
Julien Madeo, Michael K. L. Man, Chakradhar Sahoo, Marshall Campbell, Vivek Pareek, E. Laine Wong, Abdullah Al-Mahboob, Nicholas S. Chan, Arka Karmakar, Bala Murali Krishna Mariserla, Xiaoqin Li, Tony F. Heinz, Ting Cao, Keshav M. Dani
Summary: Using a table-top time-resolved ARPES setup with a MHz XUV source, we directly observed direct and momentum-forbidden excitons in the full first Brillouin zone of WSe2 monolayer, and measured their ultrafast dynamics.
2021 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)
(2021)
Article
Chemistry, Multidisciplinary
Sofiia Kosar, Andrew J. Winchester, Tiarnan A. S. Doherty, Stuart Macpherson, Christopher E. Petoukhoff, Kyle Frohna, Miguel Anaya, Nicholas S. Chan, Julien Madeo, Michael K. L. Man, Samuel D. Stranks, Keshav M. Dani
Summary: Hybrid perovskite solar cells show promise as next generation, low-cost photovoltaic technologies, but nanoscale defect clusters formed during fabrication are critical to device efficiency and stability. Research has identified different types of defect clusters and their impact on device performance, as well as the varied response of defects to passivation strategies. Tailored multi-pronged approaches are needed to selectively address the detrimental impact of different defect types in hybrid perovskite solar cells.
ENERGY & ENVIRONMENTAL SCIENCE
(2021)
Article
Materials Science, Multidisciplinary
Zhenyu Wang, Jorge Olivares, Hiromasa Namiki, Vivek Pareek, Keshav Dani, Takao Sasagawa, Vidya Madhavan, Yoshinori Okada
Summary: Recent studies have shown that Se substitution in MoTe2 can enhance superconductivity up to 1.5K but suppress the essential Td phase for the emergence of the Weyl state. This study used scanning tunneling microscopy to investigate a Se-doped MoTe1.85Se0.15 superconductor, revealing the coexistence of superconductivity and the Td phase at low temperatures.
Article
Materials Science, Multidisciplinary
K. Uchida, V Pareek, K. Nagai, K. M. Dani, K. Tanaka
Summary: Highly nonlinear optical phenomena, such as high-harmonic generation (HHG), in crystalline solids offer a unique way to access electronic properties. Using polarization-resolved HHG measurements with band-gap resonant excitation, the transition dipole moment (TDM) texture in momentum space in two-dimensional semiconductors can be probed. The study of HHG in black phosphorus reveals a crystal-orientation dependence of HHG yields and polarizations, demonstrating the potential of high-harmonic spectroscopy for probing electronic wave functions in crystalline solids.