28 results on '"Taishi Chen"'
Search Results
2. Temperature-induced anomalous magnetotransport in the Weyl semimetal Mn3Ge
- Author
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Mingxing Wu, Kouta Kondou, Taishi Chen, Satoru Nakatsuji, and Yoshichika Otani
- Subjects
General Physics and Astronomy - Abstract
The magnetic Weyl semimetallic state can lead to intriguing magnetotransport, such as chiral anomaly and the layered quantum Hall effect. Mn3X (X = Sn, Ge) is a noncollinear antiferromagnetic semimetal where a Weyl semimetallic state is stabilized by time-reversal symmetry breaking. Compared to the well-studied Mn3Sn, the Weyl fermion-induced magnetotransport in Mn3Ge has been merely studied. Here, we report an in-depth study on the magnetotransport in a microfabricated Mn3Ge single crystal from room temperature to 10 K. We reveal an anomalous anisotropic magnetoresistance with fourfold symmetry and a positive high-field longitudinal magnetoresistance below the critical temperature (160–170 K). The possible origin is the temperature-induced tilting of the Weyl nodes. Our study helps to understand the magnetotransport properties in the Weyl fermion system.
- Published
- 2023
3. Strong magnetoelastic coupling in Mn3X ( X=Ge , Sn)
- Author
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Florian Theuss, Sayak Ghosh, Taishi Chen, Oleg Tchernyshyov, Satoru Nakatsuji, and B. J. Ramshaw
- Published
- 2022
4. Identifying Native Point Defects in the Topological Insulator Bi2Te3
- Author
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Asteriona-Maria Netsou, D. A. Muzychenko, Chris Van Haesendonck, Taishi Chen, Koen Schouteden, Margriet J. Van Bael, Fengqi Song, and Heleen Dausy
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Materials science ,Condensed matter physics ,Band gap ,Doping ,Scanning tunneling spectroscopy ,Fermi level ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,0104 chemical sciences ,law.invention ,Condensed Matter::Materials Science ,symbols.namesake ,law ,Topological insulator ,symbols ,General Materials Science ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology - Abstract
We successfully identified native point defects that occur in Bi2Te3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi2Te3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi2Te3 native defects and shed light on the link between the native defects and the electronic properties of Bi2Te3, which is relevant for the synthesis of topological insulator materials and the related functional properties.
- Published
- 2020
5. Giant and Robust Anomalous Nernst Effect in a Polycrystalline Topological Ferromagnet at Room Temperature
- Author
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Zili Feng, Susumu Minami, Shuhei Akamatsu, Akito Sakai, Taishi Chen, Daisuke Nishio‐Hamane, and Satoru Nakatsuji
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Biomaterials ,Electrochemistry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2022
6. Identifying Native Point Defects in the Topological Insulator Bi
- Author
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Asteriona-Maria, Netsou, Dmitry A, Muzychenko, Heleen, Dausy, Taishi, Chen, Fengqi, Song, Koen, Schouteden, Margriet J, Van Bael, and Chris, Van Haesendonck
- Abstract
We successfully identified native point defects that occur in Bi
- Published
- 2020
7. Anomalous transverse response of Co2MnGa and universality of the room-temperature αijA/σijA ratio across topological magnets
- Author
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Satoru Nakatsuji, Akito Sakai, Linchao Ding, Benoît Fauqué, Kamran Behnia, Zengwei Zhu, Liangcai Xu, Xiaokang Li, and Taishi Chen
- Subjects
Physics ,Physical constant ,Thermal Hall effect ,Fermi level ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Topology ,01 natural sciences ,symbols.namesake ,Ferromagnetism ,Hall effect ,0103 physical sciences ,symbols ,Berry connection and curvature ,010306 general physics ,0210 nano-technology ,Bloch wave ,Nernst effect - Abstract
The off-diagonal (electric, thermal, and thermoelectric) transport coefficients of a solid can acquire an anomalous component due to the nontrivial topology of the Bloch waves. We present a study of the anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and thermal Hall effect in the Heusler-Weyl ferromagnet ${\mathrm{Co}}_{2}\mathrm{MnGa}$. The anomalous Wiedemann-Franz law, linking electric and thermal responses, was found to be valid over the whole temperature window. This indicates that the AHE has an intrinsic origin and the Berry spectrum is smooth in the immediate vicinity of the Fermi level. We extract ${\ensuremath{\alpha}}_{ij}^{A}$ from our ANE data and find that the ${\ensuremath{\alpha}}_{ij}^{A}/{\ensuremath{\sigma}}_{ij}^{A}$ ratio approaches ${k}_{B}/e$ at room temperature. Scrutinizing all topological magnets previously explored, we observe that this ratio is a sizable fraction of ${k}_{B}/e$ at room temperature. We provide a rough explanation for this feature by arguing that the two anomalous transverse coefficients depend on universal constants, the Berry curvature averaged over a window set by either the Fermi wavelength (for Hall) or the de Broglie thermal length (for Nernst). The universal scaling indicates that the widths of the two windows approaches each other at room temperature.
- Published
- 2020
8. Antichiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn3Ge
- Author
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Taishi Chen, J. S. Lin, Y. Chen, Takuro Tomita, Oleg Tchernyshyov, Collin Broholm, Matthew B. Stone, W. C. Chen, Jonathan Gaudet, Guy G. Marcus, Satoru Nakatsuji, Sayak Dasgupta, Muhammad Ikhlas, and Yonggang Zhao
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Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Phonon ,Magnetism ,Order (ring theory) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Soft modes ,Spin structure ,Neutron scattering ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
Quantum materials with strong transport responses to disparate physical quantities are of great fundamental significance and may hold technological potentials. The interplay between interactions and topology drive such responses through the effects of spontaneous symmetry breaking and the associated domain configurations on quantum transport. Here we provide a comprehensive description of the magnetism of Mn3Ge, an antiferromagnetic kagomebased semimetal with room temperature transport anomalies associated with topologically protected Weyl nodes. Using polarized neutron diffraction, we show the all-important magnetic structure is anti-chiral and coplanar carrying the symmetry of a ferromagnet without appreciable magnetization. We probe and classify the long wavelength excitations that determine its macroscopic responses including a set of collective magneto-elastic modes. We develop a phenomenological spin Hamiltonian with exchange, Dzyaloshinskii-Moriya, and crystal field interactions to describe its collective magnetism. The itinerant character of the magnetism that drives quantum transport is apparent in spin wave damping and extended magnetic interactions. Our work provides the scientific basis for manipulation of the chiral antiferromagnetic texture of Mn3Ge to control its topological quantum transport., Comment: Main text has 40 pages, 6 figures. Supplemental Information has 14 pages, 2 figures
- Published
- 2020
- Full Text
- View/download PDF
9. Iron-based binary ferromagnets for transverse thermoelectric conversion
- Author
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Susumu Minami, Motoaki Hirayama, Akito Sakai, Shinji Miwa, Tomoya Higo, Ryotaro Arita, Takuya Nomoto, Takashi Koretsune, Fumiyuki Ishii, Yangming Wang, Daisuke Nishio-Hamane, Taishi Chen, and Satoru Nakatsuji
- Subjects
Multidisciplinary ,Materials science ,Condensed matter physics ,Fermi energy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,Thermal conduction ,01 natural sciences ,symbols.namesake ,Thermoelectric generator ,0103 physical sciences ,Thermoelectric effect ,symbols ,Berry connection and curvature ,010306 general physics ,0210 nano-technology ,Nernst effect - Abstract
Thermoelectric generation using the anomalous Nernst effect (ANE) has great potential for application in energy harvesting technology because the transverse geometry of the Nernst effect should enable efficient, large-area and flexible coverage of a heat source. For such applications to be viable, substantial improvements will be necessary not only for their performance but also for the associated material costs, safety and stability. In terms of the electronic structure, the anomalous Nernst effect (ANE) originates from the Berry curvature of the conduction electrons near the Fermi energy1,2. To design a large Berry curvature, several approaches have been considered using nodal points and lines in momentum space3–10. Here we perform a high-throughput computational search and find that 25 percent doping of aluminium and gallium in alpha iron, a naturally abundant and low-cost element, dramatically enhances the ANE by a factor of more than ten, reaching about 4 and 6 microvolts per kelvin at room temperature, respectively, close to the highest value reported so far. The comparison between experiment and theory indicates that the Fermi energy tuning to the nodal web—a flat band structure made of interconnected nodal lines—is the key for the strong enhancement in the transverse thermoelectric coefficient, reaching a value of about 5 amperes per kelvin per metre with a logarithmic temperature dependence. We have also succeeded in fabricating thin films that exhibit a large ANE at zero field, which could be suitable for designing low-cost, flexible microelectronic thermoelectric generators11–13. Aluminium- and gallium-doped iron compounds show a large anomalous Nernst effect owing to a topological electronic structure, and their films are potentially suitable for designing low-cost, flexible microelectronic thermoelectric generators.
- Published
- 2019
10. Change of the short-range scattering in the graphene covered with Bi 2 O 3 clusters
- Author
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Bo Zhao, Taishi Chen, Dongzhi Fu, Yuyan Han, and Haiyang Pan
- Subjects
Materials science ,Annealing (metallurgy) ,Oxide ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,01 natural sciences ,law.invention ,Bismuth ,chemistry.chemical_compound ,law ,0103 physical sciences ,010306 general physics ,Graphene oxide paper ,Graphene ,business.industry ,Doping ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,0210 nano-technology ,business ,Bilayer graphene ,Graphene nanoribbons - Abstract
In this work, we have studied the oxidation process of the bismuth doped graphene in the ambient air. Complete oxidation of the bismuth clusters and that of the graphene are firmly confirmed. The influence of oxygen on the graphene is characterized by means of Hall measurement and SdH oscillation. All transport measurements demonstrate a hole-type doping behavior. Our work also demonstrates that the short-range scattering mechanism is enhanced in doped graphene due to accumulated O-species adsorbates after being exposed in the atmosphere for 40 days and is suppressed after annealing. This investigation may open a new perspective for fabricating the graphene metal oxide devices.
- Published
- 2016
11. Magneto-optical Kerr effect in a non-collinear antiferromagnet Mn3Ge
- Author
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Yoshichika Otani, Satoru Nakatsuji, Taishi Chen, Tomoya Higo, Hironari Isshiki, and Mingxing Wu
- Subjects
010302 applied physics ,Materials science ,Kerr effect ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Crystal system ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Magneto-optic Kerr effect ,Ferromagnetism ,Hall effect ,0103 physical sciences ,Antiferromagnetism ,Berry connection and curvature ,0210 nano-technology ,Single crystal - Abstract
Non-collinear antiferromagnet Mn3Sn is a functional material that exhibits the magneto-optical Kerr effect (MOKE) as well as the anomalous Hall effect, arising from the nonvanishing Berry curvature in the broken time-reversal symmetry lattice system likewise the ferromagnets. Mn3Ge, isostructural to Mn3Sn, is also expected to exhibit a similar MOKE but has not been demonstrated yet. In this study, we performed the MOKE measurement in a Mn3Ge single crystal and obtained a large polar MOKE signal (∼8.2 mdeg) and a longitudinal MOKE signal (∼5.6 mdeg). Furthermore, by applying hyperfine polishing and annealing to the surface, we rebuilt a homogenous surface and largely improved the reproducibility of the MOKE signal in Mn3Ge.
- Published
- 2020
12. High-Mobility Sm-Doped Bi2Se3Ferromagnetic Topological Insulators and Robust Exchange Coupling
- Author
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Wenqing Liu, Fengqi Song, Fubao Zheng, Xingchen Pan, Baolin Wang, Taishi Chen, Gerrit van der Laan, Rong Zhang, Xuefeng Wang, Baigeng Wang, Yongbing Xu, Qinfang Zhang, Guanghou Wang, and Ming Gao
- Subjects
Materials science ,Condensed matter physics ,X-ray magnetic circular dichroism ,Dopant ,Ferromagnetism ,Mechanics of Materials ,Magnetic circular dichroism ,Mechanical Engineering ,Topological insulator ,Doping ,Curie temperature ,General Materials Science ,Wave vector - Abstract
High-mobility (Smx Bi1-x )2 Se3 topological insulators (with x = 0.05) show a Curie temperature of about 52 K, and the carrier concentration and Fermi wave vector can be manipulated by intentional Te introduction with no significant influence on the Curie temperature. The origin of the ferromagnetism is attributed to the trivalent Sm dopant, as confirmed by X-ray magnetic circular dichroism and first-principles calculations. The carrier concentration is on the order of 10(19) cm(-3) and the mobility can reach about 7200 cm(2) V(-1) s(-1) with pronounced Shubnikov-de Haas oscillations.
- Published
- 2015
13. Evidence of layered transport of bulk carriers in Fe-doped Bi2Se3 topological insulators
- Author
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Jun Ge, Ming Gao, Xingchen Pan, Meng Tang, Xuefeng Wang, Bo Zhao, Fengqi Song, Taishi Chen, Jun Du, Rong Zhang, and Yongbing Xu
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Physics ,Magnetoresistance ,Condensed matter physics ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Weak localization ,Effective mass (solid-state physics) ,Geometric phase ,Ferromagnetism ,Topological insulator ,Materials Chemistry ,Topological order ,Condensed Matter::Strongly Correlated Electrons ,Surface states - Abstract
We observe quantized Hall plateaus and Shubnikov de Haas oscillations in 10 at% Fe-doped Bi2Se3 flakes. All the features of the quantum transport coincide while normalizing the field-angle variable magnetoresistance to the perpendicular direction. The Hall step gives a specific contribution of ~1 e2/h per quintuple layer. This reveals a two-dimensional (2D) transport of the bulk electrons in the topological insulators. The crystal is demonstrated with an obvious ferromagnetism. Further evidences including a Berry phase of zero, a weak localization and a large effective mass rule out the contribution of the topological surface states (SS), suggesting that a great care should be taken to pindown the transport of the topological SS in topological insulators.
- Published
- 2015
14. Scanning probe microscopy induced surface modifications of the topological insulator Bi
- Author
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Asteriona-Maria, Netsou, Umamahesh, Thupakula, Jolien, Debehets, Taishi, Chen, Brandon, Hirsch, Alexander, Volodin, Zhe, Li, Fengqi, Song, Jin, Won Seo, Steven, De Feyter, Koen, Schouteden, and Chris, Van Haesendonck
- Abstract
We investigated the topological insulator (TI) Bi
- Published
- 2017
15. Annealing-Induced Bi Bilayer on Bi2Te3 Investigated via Quasi-Particle-Interference Mapping
- Author
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Umamahesh Thupakula, Dirk Lamoen, Kyungwha Park, Jolien Debehets, Asteriona Maria Netsou, Koen Schouteden, Zhe Li, Bart Partoens, K. Govaerts, Taishi Chen, Chris Van Haesendonck, and Fengqi Song
- Subjects
Auger electron spectroscopy ,Materials science ,Condensed matter physics ,Scattering ,Bilayer ,Physics ,Scanning tunneling spectroscopy ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,law.invention ,law ,Topological insulator ,0103 physical sciences ,General Materials Science ,Density functional theory ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Surface states - Abstract
Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface. The adlayer results in n-type doping, and the atomic defects act as scattering centers of the TSS electrons. We also investigated the annealing-induced Bi bilayer surface on Bi2Te3 via voltage-dependent quasi-particle-interference (QPI) mapping of the surface local density of states and via comparison with the calculated constant-energy contours and QPI patterns. We observed closed hexagonal patterns in the Fourier transform of real-space QPI maps with secondary outer spikes. DFT calculations attribute these complex QPI patterns to the appearance of a second cone due to the surface charge transfer between the Bi bilayer and the Bi2Te3. Annealing in ultrahigh vacuum offers a facile route for tuning of the topological properties and may yield similar results for other topological materials.
- Published
- 2016
16. Experimental observation on a temperature-induced decoupling between the surface states in topological insulator nanoplates Bi2−0.15(TeSe)3+0.15
- Author
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Kang Zhang, Taishi Chen, Fengqi Song, Feng Miao, Xuefeng Wang, Haoran Lu, Haiyang Pan, Junwen Zeng, and Rong Zhang
- Subjects
Condensed matter physics ,Chemistry ,Dephasing ,02 engineering and technology ,General Chemistry ,Decoupling (cosmology) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Temperature induced ,Topological insulator ,0103 physical sciences ,General Materials Science ,010306 general physics ,0210 nano-technology ,Quantum ,Surface states - Abstract
We report on the temperature-induced quantum decoupling between the surface states, demonstrated by weak antilocalization measurements, in the topological insulator Bi2−0.15(TeSe)3+0.15 nanoplates. The samples are prepared by a catalyst-free vapor–solid process with the dimension of 10 μm and the thickness of 20 nm. The channel indicator is extracted from the weak antilocalization, which presents a transition from 0.5 to 1 with the increasing temperature. This reveals the coherent decoupling between the two surface states, during which the dephasing length reaches the plate thickness. A bulk-mediated intersurface coupling model interprets the transition.
- Published
- 2016
17. Scaling the Dynamic Electron Scattering in Imaging the Graphene Sheets by the High-Angle Annular Dark-Field Microscopy
- Author
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Taishi Chen, Jianfeng Zhou, Min Han, Longbing He, Liao Km, Guanghou Wang, W F Ding, Jianguo Wan, and Fengqi Song
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Materials science ,business.industry ,Graphene ,Scattering ,Biomedical Engineering ,Bioengineering ,General Chemistry ,Electron ,Condensed Matter Physics ,Molecular physics ,Dark field microscopy ,law.invention ,Optics ,Annular dark-field imaging ,law ,Scanning transmission electron microscopy ,Cathode ray ,General Materials Science ,business ,Electron scattering - Abstract
Employing the graphene sheets (GSs), the electron scattering constants are measured in the high-angle annular dark-field (HAADF) imaging by the scanning transmission electron microscopy. Single scattering is found to be dominant until the layer number of 200, complying with a simple relation of I = Io(1 - e(-tau/lambda)). The discrete layer counting of the GSs enables precise determination of incident depths. This work results values of lambda = 48.2, 61.4, 97.9 and 115.6 nm for 80, 120, 160 and 200 keV electrons, respectively. The uncertainties with the mean free paths and the cross sections are confined to 10 percent. The dependences on the electron beam energy and the collection angle are discussed based on a multislice simulation.
- Published
- 2012
18. Visualizing Topological Insulating Bi2Te3 Quintuple Layers on SiO2-Capped Si Substrates and Its Contrast Optimization
- Author
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Yuyuan Qin, Zhaoguo Li, Changhui Xu, Jianfeng Zhou, Taishi Chen, Guanghou Wang, Min Han, Jianguo Wan, Yue-Wen Mu, Fengqi Song, and Longbing He
- Subjects
Wavelength ,Materials science ,Diagram ,Biomedical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics ,Topology ,Layer (electronics) - Abstract
Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.
- Published
- 2011
19. High-power splitting of expanded graphite to produce few-layer graphene sheets
- Author
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Fengqi Song, Yuyuan Qin, Min Han, Taishi Chen, Jianfeng Zhou, Kaiming Liao, Bo Zhao, Guanghou Wang, Wangfeng Ding, Zhaoguo Li, and Jianguo Wan
- Subjects
Materials science ,Graphene ,Sonication ,Analytical chemistry ,General Chemistry ,law.invention ,Power (physics) ,symbols.namesake ,Few layer graphene ,law ,Scanning transmission electron microscopy ,symbols ,General Materials Science ,Graphite ,Composite material ,Raman spectroscopy ,Layer (electronics) - Abstract
Few-layer graphene sheets were prepared by splitting expanded graphite using high-power sonication. Atomic-level calibrated scanning transmission electron microscopy was used to obtain efficient layer statistics, enabling optimization of the experimental conditions. This resulted in a two-step splitting mechanism in which the mean number of layers was first reduced to less than 20 by heating to 1100 °C and then to a few-layer region by a 5-min 104 W L−1 – power-density sonication. Raman spectroscopic analysis confirms the above mechanism and demonstrates that the sheets are largely free of defects and functional groups.
- Published
- 2011
20. Experimental evidence and control of the bulk-mediated intersurface coupling in topological insulatorBi2Te2Senanoribbons
- Author
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Yuze Meng, X. C. Hong, Ion Garate, Shiyan Li, Wei Ning, Li Pi, J. Pan, Guanghou Wang, Zhaoguo Li, Xiangang Wan, Xiaoou Zhang, Mark A. Reed, Fengqi Song, Baigeng Wang, Xinran Wang, Xuefeng Wang, Leonid I. Glazman, and Taishi Chen
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Materials science ,Magnetoresistance ,Condensed matter physics ,Condensed Matter Physics ,Coupling (probability) ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Metal ,Topological insulator ,visual_art ,Phase (matter) ,Quantum interference ,visual_art.visual_art_medium ,Relaxation length - Abstract
We present evidence for the existence and control of bulk-surface coupling in ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{2}\mathrm{Se}$ nanoribbons. Our magnetoresistance measurements reveal that the number of coherent channels contributing to quantum interference in the nanoribbons changes abruptly when the film thickness exceeds the bulk phase relaxation length. We interpret this observation as an evidence for bulk-mediated coupling between metallic states located on opposite surfaces. This hypothesis is supported by additional magnetoresistance measurements conducted under a set of gate voltages and in a parallel magnetic field, the latter of which alters the intersurface coupling in a controllable way.
- Published
- 2015
21. Scanning probe microscopy induced surface modifications of the topological insulator Bi2Te3in different environments
- Author
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Zhe Li, Alexander Volodin, Brandon E. Hirsch, Asteriona-Maria Netsou, Jin Won Seo, Chris Van Haesendonck, Steven De Feyter, Koen Schouteden, Jolien Debehets, Taishi Chen, Fengqi Song, and Umamahesh Thupakula
- Subjects
Surface (mathematics) ,Auger electron spectroscopy ,Materials science ,Mechanical Engineering ,Organic solvent ,Analytical chemistry ,Bioengineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Prolonged exposure ,Scanning probe microscopy ,Adsorption ,Mechanics of Materials ,Topological insulator ,0103 physical sciences ,Nitrogen gas ,General Materials Science ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology - Abstract
We investigated the topological insulator (TI) Bi2Te3 in four different environments (ambient, ultra-high vacuum (UHV), nitrogen gas and organic solvent environment) using scanning probe microscopy (SPM) techniques. Upon prolonged exposure to ambient conditions and organic solvent environments the cleaved surface of the pristine Bi2Te3 is observed to be strongly modified during SPM measurements, while imaging of freshly cleaved Bi2Te3 in UHV and nitrogen gas shows considerably less changes of the Bi2Te3 surface. We conclude that the reduced surface stability upon exposure to ambient conditions is triggered by adsorption of molecular species from ambient, including H2O, CO2, etc which is verified by Auger electron spectroscopy. Our findings of the drastic impact of exposure to ambient on the Bi2Te3 surface are crucial for further in-depth studies of the intrinsic properties of the TI Bi2Te3 and for potential applications that include room temperature TI based devices operated under ambient conditions.
- Published
- 2017
22. Shubnikov de Haas quantum oscillation of the surface states in the metallic Bismuth Telluride sheets
- Author
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Min Han, Jianguo Wan, Rong Zhang, Junhao Han, Guanghou Wang, Bo Zhao, Xuefeng Wang, Zhaoguo Li, Fengqi Song, Taishi Chen, and Baigeng Wang
- Subjects
Physics ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Field (physics) ,Condensed matter physics ,Magnetoresistance ,Oscillation ,Quantum oscillations ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Atomic and Molecular Physics, and Optics ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,Topological insulator ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Bismuth telluride ,Condensed Matter::Strongly Correlated Electrons ,Surface states - Abstract
Metallic Bi2Te3 crystalline sheets with the room-temperature resistivity of above 10 m{\Omega} cm were prepared and their magnetoresistive transport was measured in a field of up to 9 Tesla. The Shubnikov de Haas oscillations were identified from the secondly-derived magnetoresistance curves. While changing the angle between the field and normal axis of the sheets, we find that the oscillation periods present a cosine dependence on the angle. This indicates a two-dimensional transport due to the surface state. The work reveals a resolvable surface contribution to the overall conduction even in a metallic topological insulator., Comment: accepted by EPJD, 2013
- Published
- 2013
- Full Text
- View/download PDF
23. Electronic interference transport and its electron–phonon interaction in the Sb-doped Bi2Se3nanoplates synthesized by a solvothermal method
- Author
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Taishi Chen, Fucong Fei, Haiyang Pan, Yuyan Han, and Bo Zhao
- Subjects
Materials science ,Field (physics) ,Condensed matter physics ,Magnetoresistance ,Dephasing ,Doping ,chemistry.chemical_element ,Condensed Matter Physics ,Antimony ,chemistry ,Perpendicular ,General Materials Science ,Spin (physics) ,Universal conductance fluctuations - Abstract
Here we synthesized the antimony doped [Formula: see text] nanoplates by the solvothermal method. The angle-dependent magnetoconductance study was carried out and all the [Formula: see text] were found to be normalized to the perpendicular field, indicating a clear 2D electronic state. The features of weak antilocalization and universal conductance fluctuations were clearly identified in the magnetoresistance transport of the 4-probe nanodevices. The dephasing lengths are extracted respectively according to the Hikami-Larkin-Nagaoka theory. It is attributed to the involvement of the dynamic spin centers. The dephasing lengths are found to increase with the decreasing temperature following a [Formula: see text] law with [Formula: see text]. This reveals the additional dephasing source of electron-phonon interaction, which is often absent for pure 2D electronic systems.
- Published
- 2015
24. In situ cleavage prepared bilayer graphene device and its large magnetoresistance
- Author
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Bo Zhao, Haiyang Pan, Peng Mao, and Taishi Chen
- Subjects
In situ ,Materials science ,Magnetoresistance ,Graphene ,Nanotechnology ,Cleavage (crystal) ,Electron ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Irradiation ,Bilayer graphene ,Instrumentation ,Lithography - Abstract
A Zn-based in situ cleavage method is applied to fabricate few-layer graphene devices. This approach avoids unintentional electron-beam irradiation damage, in addition to creating a series of clean graphene devices with well controlled layer numbers. As prepared bilayer graphene surprisingly achieves a magnetoresistance ratio as high as 350% at 1.9 K and 100% at room temperature. For this reason, in situ cleavage method/electron-beam lithographic could provide a more effective way to fabricate modern day carbon electronic components.
- Published
- 2015
25. Visualizing topological insulating Bi2Te3 quintuple layers on SiO2-capped Si substrates and its contrast optimization
- Author
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Zhaoguo, Li, Yuyuan, Qin, Yuewen, Mu, Taishi, Chen, Changhui, Xu, Longbing, He, Jianguo, Wan, Fengqi, Song, Jianfeng, Zhou, Min, Han, and Guanghou, Wang
- Abstract
Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.
- Published
- 2011
26. Scaling the dynamic electron scattering in HAADF-imaging the graphene sheets
- Author
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Fengqi Song, G.H. Wang, Min Han, L. B. He, Jianguo Wan, Jian Zhou, W F Ding, Kaiming Liao, and Taishi Chen
- Subjects
Materials science ,business.industry ,Graphene ,Analytical chemistry ,Dark field microscopy ,law.invention ,Formvar ,Transmission electron microscopy ,law ,Scanning transmission electron microscopy ,Optoelectronics ,Graphite ,business ,Field emission gun ,Electron scattering - Abstract
Free-standing graphene sheets (GS) with several to over a hundred layers are prepared by splitting the expandable graphite. The raw material is firstly transferred to a heating chamber for the thermal flashing at 1500 οC in a hydrogen chamber. The expanded powder (1 mg) is then dispersed in 10 ml of the PmPV/DCE suspension for high-power sonication and further centrifugation. After drop-cast onto a holey Formvar film, the GSs are suspended on the grid. The electron scattering is carried out in a Tecnai F20 TEM/STEM with a field emission gun. A high-angle annular dark field (HAADF) detector is fitted to collect the scattered electrons with a tunable collecting angle. The quantitative STEM image simulation is carried out using amultislice algorithm [4].
- Published
- 2010
27. Indications of topological transport by universal conductance fluctuations in Bi2Te2Se microflakes
- Author
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J. Pan, Taishi Chen, Xuefeng Wang, Baigeng Wang, Shiyan Li, X. C. Hong, Fengqi Song, Yuze Meng, and Zhaoguo Li
- Subjects
Physics ,Amplitude ,Magnetoresistance ,Ensemble average ,General Engineering ,General Physics and Astronomy ,Electron ,Topology ,Coherence (physics) ,Surface states ,Universal conductance fluctuations - Abstract
Universal conductance fluctuations (UCFs) are extracted in the magnetoresistance responses in bulk-insulating Bi2Te2Se microflakes. Their two-dimensional character is demonstrated by field-tilting magnetoresistance measurements. Their origin from the surface electrons is determined by the fact that the UCF amplitudes remain unchanged while applying an in-plane field to suppress the coherence of bulk electrons. After considering the ensemble average in a batch of micrometer-sized samples, the intrinsic UCF magnitude of over 0.37 e2/h is obtained. This agrees with the theoretical prediction on topological surface states. All the lines of evidence point to the successful observation of the UCF of topological surface states.
- Published
- 2014
28. Fiber optic sensor for hydrogen detection near explosive limit
- Author
-
Richard Wills, Rama Vuppuladhadium, Taishi Chen, and Samhita Dasgupta
- Subjects
Materials science ,Explosive material ,Hydrogen ,chemistry ,business.industry ,Fiber optic sensor ,Optoelectronics ,chemistry.chemical_element ,Limit (mathematics) ,business - Published
- 1999
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