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Advanced materials 2019年第43期58卷 15601-15609页

作者： Kumar, Ventrapati Pavan Guélou, Gabin Lemoine, Pierric Raveau, Bernard Supka, Andrew R. Orabi, Rabih Al Rahal Al Fornari, Marco Suekuni, Koichiro Guilmeau, Emmanuel CRISMAT CNRS Normandie Univ ENSICAEN UNICAEN Caen14000 France Univ Rennes CNRS ISCR – UMR 6226 Rennes35000 France Department of Physics and Science of Advanced Materials Program Central Michigan University Mt. PleasantMI48859 United States Department of Applied Science for Electronics and Materials Interdisciplinary Graduate School of Engineering Sciences Kyushu University Kasuga Fukuoka816-8580 Japan Solvay Design and Development of Functional Materials Department Axel’One 87 avenue des Frères Perret Saint Fons Cedex69192 France

Herein, we investigate the Mo andWsubstitution for Cr in synthetic colusite, Cu26Cr2Ge6S32. Primarily, we elucidate the origin of extremely low electrical resistivity which does not compromise the Seebeck coefficient and leads to outstanding power factors of 1.94 mWm−1K−2 at 700 K in Cu26Cr2Ge6S32. We demonstrate that the abnormally long iono-covalent T–S bonds competing with short metallic Cu–T interactions govern the electronic transport properties of the conductive „Cu26S32" framework. We address the key role of the cationic size-mismatch at the core of the mixed tetrahedral–octahedral complex over the transport properties. Two essential effects are identified: 1) only the tetrahedra that are directly bonded to the [TS4]Cu6 complex are significantly distorted upon substitution and 2) the major contribution to the disorder is localized at the central position of the mixed tetrahedral–octahedral complex, and is maximized for x=1, i.e. for the highest cationic sizevariance, σ2. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

关键词： Copper compounds

Interaction-driven transport of dark excitons in 2D semiconductors with phonon-mediated optical readout

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arXiv 2022年

作者： Chand, Saroj B. Woods, John M. Quan, Jiamin Mejia, Enrique Taniguchi, Takashi Watanabe, Kenji Alù, Andrea Grosso, Gabriele Photonics Initiative Advanced Science Research Center City University of New York New YorkNY10031 United States International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Electrical Engineering City College of the City University of New York New YorkNY10031 United States Physics Program Graduate Center City University of New York New YorkNY10016 United States

The growing field of quantum information technology requires propagation of information over long distances with efficient readout mechanisms. Excitonic quantum fluids have emerged as a powerful platform for this task due to their straightforward electro-optical conversion. In two-dimensional transition metal dichalcogenides, the coupling between spin and valley provides exciting opportunities for harnessing, manipulating and storing bits of information. However, the large inhomogeneity of single layers cannot be overcome by the properties of bright excitons, hindering spin-valley transport. Nonetheless, the rich band structure supports dark excitonic states with strong binding energy and longer lifetime, ideally suited for long-range transport. Here we show that dark excitons can diffuse over several micrometers and prove that this repulsion-driven propagation is robust across non-uniform samples. The long-range propagation of dark states with an optical readout mediated by chiral phonons provides a new concept of excitonic devices for applications in both classical and quantum information technology. Copyright © 2022, The Authors. All rights reserved.

关键词： Sulfur compounds

Surface buckling of phosphorene materials: Determination, origin and influence on electronic structure

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arXiv 2017年

作者： Dai, Zhongwei Jin, Wencan Yu, Jie-Xiang Grady, Maxwell Sadowski, Jerzy T. Kim, Young Duck Hone, James Zang, Jiadong Osgood, Richard M. Pohl, Karsten Department of Physics and Materials Science Program University of New Hampshire DurhamNH03824 United States Columbia University New YorkNY10027 United States Center for Functional Nanomaterials Brookhaven National Laboratory UptonNY11973 United States Department of Physics University of Michigan Ann ArborMI48109 United States Department of Physics Center for Humanities and Sciences Kyung Hee University Seoul02447 Korea Republic of

The surface structure of phosphorene crystals materials is determined using surface sensitive dynamical micro-spot low energy electron diffraction (μLEED) analysis using a high spatial resolution low energy electron microscopy (LEEM) system. Samples of (i) crystalline cleaved black phosphorus (BP) at 300 K and (ii) exfoliated few-layer phosphorene (FLP) of about 10 nm thicknes, which were annealed at 573 K in vacuum were studied. In both samples, a significant surface buckling of 0.22 Å and 0.30 Å, respectively, is measured, which is one order of magnitude larger than previously reported. Using first principle calculations, the presence of surface vacancies is attributed not only to the surface buckling in BP and FLP, but also the previously reported intrinsic hole doping of phosphorene materials. Copyright © 2017, The Authors. All rights reserved.

关键词： Electrons

Characterization and Development of Ceo2 Nanoparticles in Zn-Doped Ceo2/Rgo Nanocomposites

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SSRN

SSRN 2024年

作者： Phokha, Sumalin Utara, Songkot Salidkul, Nuchjaree Karaphun, Attaphol Sonsupap, Somchai Chanlek, Narong Hunpratub, Sitchai Functional Materials and Composites Research Group Faculty of Science Udon Thani Rajabhat University Udon Thani41000 Thailand Advanced Nanocomposites Materials Research Group Faculty of Science Udon Thani Rajabhat University Udon Thani41000 Thailand Department of Chemistry Faculty of Science Udon Thani Rajabhat University Udon Thani41000 Thailand Materials Science and Nanotechnology Program Department of Physics Faculty of Science Khon Kaen University Khon Kaen40002 Thailand College of Innovation and Industrial Management King Mongkut’s Institute of Technology Ladkrabang Chalongkrung Road Ladkrabang Bangkok10520 Thailand 111 University Avenue Muang District Nakhon Ratchasima30000 Thailand Department of Physics Faculty of Science Udon Thani Rajabhat University Udon Thani41000 Thailand

The properties of CeO2 nanoparticles were improved by forming Zn-doped CeO2 nanoparticles at 0, 5, 10, 15 and 20 at.% with reduced graphene oxide (rGO). All samples of Zn‑doped CeO2/rGO were synthesized using a hydrothermal method, heating them at 150 °C for 12 h followed by processing in an ultrasonic reactor (20 kHz) at 25±1 oC. These samples exhibited a single CeO2 phase corresponding to a face centered cubic structure, except for 20 at.% Zn‑doped CeO2/rGO which presented a ZnO phase. The samples had band gap values lower than expected for undoped CeO2 nanoparticles, higher valence states due to their Ce3+/Ce4+ ratio and a large surface area, 242 m2/g, because of Zn doping in CeO2 samples. The highest specific capacitance value, 43 F/g at 2 mV/s for the 5 at.% Zn‑doped CeO2/rGO, was achieved. Zn doping enabled good capacitive behavior which was caused by the Ce3+/Ce4+ ratio effects © 2024, The Authors. All rights reserved.

关键词： Nanocomposites

Improved Optical and Electrochemical Performance of Ceo2 Nanoparticles in Zn-Doped Ceo2/Rgo Nanocomposites

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SSRN

SSRN 2024年

The optical and electrochemical properties of CeO2 nanoparticles were improved by forming Zn-doped CeO2 nanoparticles at levels of 0, 5, 10, 15 and 20% of Zn with reduced graphene oxide (rGO) referred to in this report as CeO2/rGO, Zn5-CeO2/rGO, Zn10-CeO2/rGO, Zn15-CeO2/rGO and Zn20-CeO2/rGO, respectively. All samples of Zn-doped CeO2/rGO nanocomposites were synthesized using a hydrothermal method, heating them at 150 °C for 12 h followed by processing in an ultrasonic reactor (20 kHz) at 25±1 oC for 1 h. Undoped CeO2 nanoparticles with no rGO were also studied after processing under the same conditions for comparison. The phase, morphology, optical, valence states, surface area and specific capacitance of prepared samples were characterized. These samples exhibited X-ray diffraction patterns of a single CeO2 phase corresponding to a face centered cubic structure, except for the Zn20-CeO2/rGO nanocomposites which presented a ZnO phase. The calculated average crystallite sizes of CeO2 peaks were in the range of 4.60 ± 0.2 to 12.0 ± 0.4 nm. Sample measurements confirmed formation of a composite consisting of CeO2 nanoparticles and rGO. The synthesized samples had band gap values lower than expected for undoped CeO2 nanoparticles, higher valence states due to their Ce3+/Ce4+ ratio and a large surface area, 242 m2/g, because of Zn doping in CeO2 samples. The highest specific capacitance value, 43 F/g at 2 mV/s for the Zn5-CeO2/rGO nanocomposites, was achieved. This is about 3.9 times higher than that of undoped CeO2 nanoparticles. The charge transfer resistance of the synthesized samples was obtained. Zn doping enabled good capacitive behavior which was caused by the Ce3+/Ce4+ ratio effects. © 2024, The Authors. All rights reserved.

关键词： Nanocomposites

Observation of Topologically Protected Edge States in a Photonic Two-Dimensional Quantum Walk

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Physical Review Letters 2018年第10期121卷 100502-100502页

作者： Chao Chen Xing Ding Jian Qin Yu He Yi-Han Luo Ming-Cheng Chen Chang Liu Xi-Lin Wang Wei-Jun Zhang Hao Li Li-Xing You Zhen Wang Da-Wei Wang Barry C. Sanders Chao-Yang Lu Jian-Wei Pan Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics University of Science and Technology of China Shanghai Branch Shanghai 201315 China CAS-Alibaba Quantum Computing Laboratory CAS Centre for Excellence in Quantum Information and Quantum Physics Shanghai 201315 China State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology (SIMIT) Department of Physics Zhejiang University Hangzhou Zhejiang 310027 China Institute for Quantum Science and Technology University of Calgary Alberta T2N 1N4 Canada Program in Quantum Information Science Canadian Institute for Advanced Research Toronto Ontario M5G 1Z8 Canada

Periodically driven systems have displayed a variety of fascinating phenomena without analogies in static systems, which enrich the classification of quantum phases of matter and stimulate a wide range of research interests. Here, we employ discrete-time quantum walks to investigate a nontrivial topological effect unique to a two-dimensional periodically driven system: chiral edge states can exist at the interface of Floquet insulators whose Chern numbers vanish. Thanks to a resource-saving and flexible fiber-loop architecture, we realize inhomogeneous two-dimensional quantum walks up to 25 steps, over an effective 51×51 lattice with tunable local parameters. Spin-polarized chiral edge states are observed at the boundary of two distinct quantum walk domains. Our results contribute to establishing a well-controlled platform for exploring nontrivial topological phases.

关键词： Quantum simulation Quantum states of light Quantum walks Topological effects in photonic systems Topological insulators

Valley-polarized Exitonic Mott Insulator in WS2/WSe2 Moiré Superlattice

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arXiv 2023年

作者： Lian, Zhen Meng, Yuze Ma, Lei Maity, Indrajit Yan, Li Wu, Qiran Huang, Xiong Chen, Dongxue Chen, Xiaotong Chen, Xinyue Blei, Mark Taniguchi, Takashi Watanabe, Kenji Tongay, Sefaattin Lischner, Johannes Cui, Yong-Tao Shi, Su-Fei Department of Chemical and Biological Engineering Rensselaer Polytechnic Institute TroyNY12180 United States Departments of Materials The Thomas Young Centre for Theory and Simulation of Materials Imperial College London United Kingdom Department of Physics and Astronomy University of California RiversideCA92521 United States Department of Materials Science and Engineering University of California RiversideCA92521 United States Materials Science and Engineering Program School for Engineering of Matter Transport and Energy Arizona State University TempeAZ85287 United States International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Electrical Computer & Systems Engineering Rensselaer Polytechnic Institute TroyNY12180 United States

Strongly enhanced electron-electron interaction in semiconducting moiré superlattices formed by transition metal dichalcogenides (TMDCs) heterobilayers has led to a plethora of intriguing fermionic correlated states1–7. Meanwhile, interlayer excitons in a type-II aligned TMDC heterobilayer moiré superlattice, with electrons and holes separated in different layers8,9, inherit this enhanced interaction and strongly interact with each other, promising for realizing tunable correlated bosonic quasiparticles10,11 with valley degree of freedom. We employ photoluminescence spectroscopy to investigate the strong repulsion between interlayer excitons and correlated electrons in a WS2/WSe2 moiré superlattice and combine with theoretical calculations to reveal the spatial extent of interlayer excitons and the band hierarchy of correlated states. We further find that an excitonic Mott insulator state emerges when one interlayer exciton occupies one moiré cell, evidenced by emerging photoluminescence peaks under increased optical excitation power. Double occupancy of excitons in one unit cell requires overcoming the energy cost of exciton-exciton repulsion of about 30-40 meV, depending on the stacking configuration of the WS2/WSe2 heterobilayer. Further, the valley polarization of the excitonic Mott insulator state is enhanced by nearly one order of magnitude. Our study demonstrates the WS2/WSe2 moiré superlattice as a promising platform for engineering and exploring new correlated states of fermion, bosons, and a mixture of both12 © 2023, CC BY.

关键词： Excitons

Phonons become chiral in the pseudogap phase of cuprates

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arXiv 2020年

作者： Grissonnanche, G. Thériault, S. Gourgout, A. Boulanger, M.-E. Lefrançois, E. Ataei, A. Laliberté, F. Dion, M. Zhou, J.-S. Pyon, S. Takayama, T. Takagi, H. Doiron-Leyraud, N. Taillefer, L. Département de Physique Institut Quantique RQMP Université de Sherbrooke SherbrookeQC Canada Materials Science and Engineering Program Department of Mechanical Engineering University of Texas AustinTX United States Department of Advanced Materials Science University of Tokyo Kashiwa Japan Department of Applied Physics University of Tokyo Tokyo Japan Max Planck Institute for Solid State Research Stuttgart Germany Department of Physics University of Tokyo Tokyo Japan Institute for Functional Matter and Quantum Technologies University of Stuttgart Stuttgart Germany Canadian Institute for Advanced Research TorontoON Canada

The nature of the pseudogap phase of cuprates remains a major puzzle1,2. One of its new signatures is a large negative thermal Hall conductivity Èxy , which appears for dopings p below the pseudogap critical doping p*, but whose origin is as yet unknown3. Because this large Èxy is observed even in the undoped Mott insulator La2CuO4, it cannot come from charge carriers, these being localized at p = 0. Here we show that the thermal Hall conductivity of La2CuO4 is roughly isotropic, being nearly the same for heat transport parallel and normal to the CuO2planes, i.e. kzy(T) . (T). This shows that the Hall response must come from phonons, these being the only heat carriers able to move as easily normal and parallel to the planes4. At p > p*, in both La1.6-xNd0.4SrxCuO4and La1.8-xEu0.2SrxCuO4with p = 0.24, we observe no c-axis Hall signal, i.e. zy(T) = 0, showing that phonons have zero Hall response outside the pseudogap phase. The phonon Hall response appears immediately below p*= 0.23, as confirmed by the large Kzy signal we find in La1.6-xNd0.4SrxCuO4with p = 0.21. The microscopic mechanism by which phonons become chiral in cuprates remains to be identified. This mechanism must be intrinsic-from a coupling of phonons to their electronic environment-rather than extrinsic, from structural defects or impurities, as these are the same on both sides of p*. This intrinsic phonon Hall effect provides a new window on quantum materials5 and it may explain the thermal Hall signal observed in other topologically nontrivial insulators6,7. Copyright © 2020, The Authors. All rights reserved.

关键词： Phonons

Topological flat bands in a family of multilayer graphene moiré lattices

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arXiv 2024年

作者： Waters, Dacen Su, Ruiheng Thompson, Ellis Okounkova, Anna Arreguin-Martinez, Esmeralda He, Minhao Hinds, Katherine Watanabe, Kenji Taniguchi, Takashi Xu, Xiaodong Zhang, Ya-Hui Folk, Joshua Yankowitz, Matthew Department of Physics University of Washington SeattleWA98195 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA98195 United States Stewart Blusson Quantum Matter Institute University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics and Astronomy University of British Columbia VancouverBCV6T 1Z1 Canada Department of Materials Science and Engineering University of Washington SeattleWA98195 United States Department of Physics Princeton University PrincetonNJ08544 United States Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Physics and Astronomy Johns Hopkins University BaltimoreMD21205 United States

Moiré materials host a wealth of intertwined correlated and topological states of matter, all arising from flat electronic bands with nontrivial quantum geometry [1, 2]. A prominent example is the family of alternating-twist magic-angle graphene stacks, which exhibit symmetry-broken states at rational fillings of the moiré band and superconductivity close to half filling [3–7]. Here, we introduce a second family of twisted graphene multilayers made up of twisted sheets of M- and N-layer Bernal-stacked graphene flakes. Calculations indicate that applying an electric displacement field isolates a flat and topological moiré conduction band that is primarily localized to a single graphene sheet below the moiré interface. Phenomenologically, the result is a striking similarity in the hierarchies of symmetry-broken phases across this family of twisted graphene multilayers. Our results show that this family of structures offers promising new opportunities for the discovery of exotic new correlated and topological phenomena, enabled by using the layer number to fine tune the flat moiré band and its screening environment. Copyright © 2024, The Authors. All rights reserved.

关键词： Graphene

Layer-dependent optically-induced spin polarization in InSe

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arXiv 2022年

作者： Nelson, Jovan Stanev, Teodor K. Lebedev, Dmitry LaMountain, Trevor Tyler Gish, J. Zeng, Hongfei Shin, Hyeondeok Heinonen, Olle Watanabe, Kenji Taniguchi, Takashi Hersam, Mark C. Stern, Nathaniel P. Applied Physics Program Northwestern University EvanstonIL60208 United States Department of Physics and Astronomy Northwestern University EvanstonIL60208 United States Department of Material Science & Engineering Northwestern University EvanstonIL60208 United States Computational Science Division Argonne National Laboratory LemontIL60439 United States Material Science Division Argonne National Laboratory LemontIL60439 United States Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Chemistry Northwestern University EvanstonIL60208 United States Department of Electrical Engineering and Computer Science Northwestern University EvanstonIL60208 United States

Optical control of spin in semiconductors has been pioneered using nanostructures of III-V and II-VI semiconductors, but the emergence of two-dimensional van der Waals materials offers an alternative low-dimensional platform for spintronic phenomena. Indium selenide (InSe), a group-III monochalcogenide van der Waals material, has shown promise for opto-electronics due to its high electron mobility, tunable direct bandgap, and quantum transport. In addition to these confirmed properties, there are predictions of spin-dependent optical selection rules suggesting potential for all-optical excitation and control of spin in a two-dimensional layered material. Despite these predictions, layer-dependent optical spin phenomena in InSe have yet to be explored. Here, we present measurements of layer-dependent optical spin dynamics in few-layer and bulk InSe. Polarized photo-luminescence reveals layer-dependent optical orientation of spin, thereby demonstrating the optical selection rules in few-layer InSe. Spin dynamics are also studied in many-layer InSe using time-resolved Kerr rotation spectroscopy. By applying out-of-plane and in-plane static magnetic fields for polarized emission measurements and Kerr measurements, respectively, the g-factor for InSe was extracted. Further investigations are done by calculating precession values using a k·p model, which is supported by ab-initio density functional theory. Comparison of predicted precession rates with experimental measurements highlights the importance of excitonic effects in InSe for understanding spin dynamics. Optical orientation of spin is an important prerequisite for opto-spintronic phenomena and devices, and these first demonstrations of layer-dependent optical excitation of spins in InSe lay the foundation for combining layer-dependent spin properties with advantageous electronic properties found in this material. Copyright © 2022, The Authors. All rights reserved.

关键词： Spin dynamics