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Yu M, Iddawela SA, Wang J, Hilse M, Thompson JL, Reifsnyder Hickey D, Sinnott SB, Law S. Quasi-Van der Waals Epitaxial Growth of γ'-GaSe Nanometer-Thick Films on GaAs(111)B Substrates. ACS NANO 2024; 18:17185-17196. [PMID: 38870462 DOI: 10.1021/acsnano.4c04194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2024]
Abstract
GaSe is an important member of the post-transition-metal chalcogenide family and is an emerging two-dimensional (2D) semiconductor material. Because it is a van der Waals material, it can be fabricated into atomic-scale ultrathin films, making it suitable for the preparation of compact, heterostructure devices. In addition, GaSe possesses unusual optical and electronic properties, such as a shift from an indirect-bandgap single-layer film to a direct-bandgap bulk material, rare intrinsic p-type conduction, and nonlinear optical behaviors. These properties make GaSe an appealing candidate for the fabrication of field-effect transistors, photodetectors, and photovoltaics. However, the wafer-scale production of pure GaSe single-crystal thin films remains challenging. This study develops an approach for the direct growth of nanometer-thick GaSe films on GaAs substrates by using molecular beam epitaxy. It yields smooth thin GaSe films with a rare γ'-polymorph. We analyze the formation mechanism of γ'-GaSe using density-functional theory and speculate that it is stabilized by Ga vacancies since the formation enthalpy of γ'-GaSe tends to become lower than that of other polymorphs when the Ga vacancy concentration increases. Finally, we investigate the growth conditions of GaSe, providing valuable insights for exploring 2D/three-dimensional (3D) quasi-van der Waals epitaxial growth.
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Affiliation(s)
- Mingyu Yu
- Department of Materials Science and Engineering, University of Delaware, 201 Dupont Hall, 127 The Green, Newark, Delaware 19716, United States
| | - Sahani Amaya Iddawela
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Jiayang Wang
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Maria Hilse
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Jessica L Thompson
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Danielle Reifsnyder Hickey
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Susan B Sinnott
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Institute for Computational and Data Science, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Penn State Institute of Energy and the Environment, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Stephanie Law
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Penn State Institute of Energy and the Environment, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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2
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Kumar N, Surovtsev NV, Yunin PA, Ishchenko DV, Milekhin IA, Lebedev SP, Lebedev AA, Tereshchenko OE. Raman scattering spectroscopy of MBE grown thin film topological insulator Bi 2-xSb xTe 3-ySe y. Phys Chem Chem Phys 2024; 26:13497-13505. [PMID: 38651229 DOI: 10.1039/d4cp01169d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
BSTS epitaxial thin film topological insulators were grown using the MBE technique on two different types of substrates i.e., Si (111) and SiC/graphene with Bi0.7Sb1.6Te1.8Se0.9 and Bi0.9Sb1.5Te1.8Se1.1, respectively. The crystallographic properties of BSTS films were investigated via X-ray diffraction, which showed the strongest reflections from the (0 0 l) facets corresponding to the rhombohedral phase. Superior epitaxial growth, homogeneous thickness, smooth surfaces, and larger unit cell parameters were observed for the films grown on the Si substrate. Polarization dependent Raman spectroscopy showed a weak appearance of the Ag mode in cross--polarized geometry. In contrast, a strong Eg mode was observed in both parallel and cross-polarized geometries which correspond to the rhombohedral crystal symmetry of BSTS films. A redshift of Ag and Eg modes was observed in the Raman spectra of BSTS films grown on the Si substrate, compared to those on SiC/graphene, which was directly associated with the unit cell parameter and composition of the films. Raman spectra showed four fundamental modes with asymmetric line shape, and deconvolution of the peaks resulted in additional modes in both the BSTS thin films. The sum of relative ratios of linewidths of fundamental modes (Ag and Eg) of BSTS films grown on Si substrate was lower, indicating a more ordered structure with lower contribution of defects as compared to BSTS film grown on SiC/graphene substrate.
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Affiliation(s)
- N Kumar
- Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia.
- Faculty of Physics, Tomsk State University, 36 Lenin Ave., Tomsk 634050, Russia
| | - N V Surovtsev
- Institute of Automation and Electrometry, SB, RAS, Novosibirsk, 630090, Russia
| | - P A Yunin
- Institute for Physics of Microstructures, RAS, Afonino, Nizhny Novgorod 603087, Russia
- Faculty of Radiophysics, Lobachevsky State University, Nizhny Novgorod 603950, Russia
| | - D V Ishchenko
- Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia.
| | - I A Milekhin
- Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia.
- Novosibirsk State University, Novosibirsk, 630090, Russia
| | - S P Lebedev
- Ioffe Institute, 194021 St. Petersburg, Russia
| | - A A Lebedev
- Ioffe Institute, 194021 St. Petersburg, Russia
| | - O E Tereshchenko
- Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia.
- Synchrotron Radiation Facility SKIF, Boreskov Institute of Catalysis, SB, RAS, Koltsovo 630559, Russia
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Yi H, Zhao YF, Chan YT, Cai J, Mei R, Wu X, Yan ZJ, Zhou LJ, Zhang R, Wang Z, Paolini S, Xiao R, Wang K, Richardella AR, Singleton J, Winter LE, Prokscha T, Salman Z, Suter A, Balakrishnan PP, Grutter AJ, Chan MHW, Samarth N, Xu X, Wu W, Liu CX, Chang CZ. Interface-induced superconductivity in magnetic topological insulators. Science 2024; 383:634-639. [PMID: 38330133 DOI: 10.1126/science.adk1270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 01/10/2024] [Indexed: 02/10/2024]
Abstract
The interface between two different materials can show unexpected quantum phenomena. In this study, we used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (TI) and an antiferromagnetic iron chalcogenide (FeTe). We observed emergent interface-induced superconductivity in these heterostructures and demonstrated the co-occurrence of superconductivity, ferromagnetism, and topological band structure in the magnetic TI layer-the three essential ingredients of chiral topological superconductivity (TSC). The unusual coexistence of ferromagnetism and superconductivity is accompanied by a high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. These magnetic TI/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics.
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Affiliation(s)
- Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ying-Ting Chan
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
| | - Jiaqi Cai
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Ruobing Mei
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Xianxin Wu
- CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Zi-Jie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Zihao Wang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Stephen Paolini
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Run Xiao
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ke Wang
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | - Anthony R Richardella
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | - John Singleton
- National High Magnetic Field Laboratory, Los Alamos, NM 87544, USA
| | - Laurel E Winter
- National High Magnetic Field Laboratory, Los Alamos, NM 87544, USA
| | - Thomas Prokscha
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Zaher Salman
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Andreas Suter
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Purnima P Balakrishnan
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Alexander J Grutter
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Nitin Samarth
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA 98195, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA
| | - Weida Wu
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
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4
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Guo J, Dai X, Zhang L, Li H. Electron Transport Properties of Graphene/WS 2 Van Der Waals Heterojunctions. Molecules 2023; 28:6866. [PMID: 37836709 PMCID: PMC10574387 DOI: 10.3390/molecules28196866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 09/26/2023] [Accepted: 09/27/2023] [Indexed: 10/15/2023] Open
Abstract
Van der Waals heterojunctions of two-dimensional atomic crystals are widely used to build functional devices due to their excellent optoelectronic properties, which are attracting more and more attention, and various methods have been developed to study their structure and properties. Here, density functional theory combined with the nonequilibrium Green's function technique has been used to calculate the transport properties of graphene/WS2 heterojunctions. It is observed that the formation of heterojunctions does not lead to the opening of the Dirac point of graphene. Instead, the respective band structures of both graphene and WS2 are preserved. Therefore, the heterojunction follows a unique Ohm's law at low bias voltages, despite the presence of a certain rotation angle between the two surfaces within the heterojunction. The transmission spectra, the density of states, and the transmission eigenstate are used to investigate the origin and mechanism of unique linear I-V characteristics. This study provides a theoretical framework for designing mixed-dimensional heterojunction nanoelectronic devices.
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Affiliation(s)
- Junnan Guo
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China;
| | - Xinyue Dai
- Materdicine Lab, School of Life Sciences, Shanghai University, Shanghai 200444, China;
| | - Lishu Zhang
- Peter Grünberg Institut (PGI-1) and Institute for Advanced Simulation (IAS-1), Forschungszentrum Jülich, Jülich 52428, Germany;
| | - Hui Li
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China;
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Mulder L, van de Glind H, Brinkman A, Concepción O. Enhancement of the Surface Morphology of (Bi 0.4Sb 0.6) 2Te 3 Thin Films by In Situ Thermal Annealing. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:763. [PMID: 36839131 PMCID: PMC9961334 DOI: 10.3390/nano13040763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/13/2023] [Accepted: 02/15/2023] [Indexed: 06/18/2023]
Abstract
The study of the exotic properties of the surface states of topological insulators requires defect-free and smooth surfaces. This work aims to study the enhancement of the surface morphology of optimally doped, high-crystalline (Bi0.4Sb0.6)2Te3 films deposited by molecular beam epitaxy on Al2O3 (001) substrates. Atomic force microscopy shows that by employing an in situ thermal post anneal, the surface roughness is reduced significantly, and transmission electron microscopy reveals that structural defects are diminished substantially. Thence, these films provide a great platform for the research on the thickness-dependent properties of topological insulators.
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Affiliation(s)
- Liesbeth Mulder
- MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
| | - Hanne van de Glind
- MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
| | - Alexander Brinkman
- MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
| | - Omar Concepción
- MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
- Peter Grünberg Institute (PGI-9), Forschungszentrum Juelich, 52425 Juelich, Germany
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6
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Li CH, Moon J, van 't Erve OMJ, Wickramaratne D, Cobas ED, Johannes MD, Jonker BT. Spin-Sensitive Epitaxial In 2Se 3 Tunnel Barrier in In 2Se 3/Bi 2Se 3 Topological van der Waals Heterostructure. ACS APPLIED MATERIALS & INTERFACES 2022; 14:34093-34100. [PMID: 35820066 DOI: 10.1021/acsami.2c08053] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Current-generated spin arising from spin-momentum locking in topological insulator (TI) surface states has been shown to switch the magnetization of an adjacent ferromagnet (FM) via spin-orbit torque (SOT) with a much higher efficiency than heavy metals. However, in such FM/TI heterostructures, most of the current is shunted through the FM metal due to its lower resistance, and recent calculations have also shown that topological surface states can be significantly impacted when interfaced with an FM metal such as Ni and Co. Hence, placing an insulating layer between the TI and FM will not only prevent current shunting, therefore minimizing overall power consumption, but may also help preserve the topological surface states at the interface. Here, we report the van der Waals epitaxial growth of β-phase In2Se3 on Bi2Se3 by molecular beam epitaxy and demonstrate its spin sensitivity by the electrical detection of current-generated spin in Bi2Se3 surface states using a Fe/In2Se3 detector contact. Our density functional calculations further confirm that the linear dispersion and spin texture of the Bi2Se3 surface states are indeed preserved at the In2Se3/Bi2Se3 interface. This demonstration of an epitaxial crystalline spin-sensitive barrier that can be grown directly on Bi2Se3, and verification that it preserves the topological surface state, is electrically insulating and spin-sensitive, is an important step toward minimizing overall power consumption in SOT switching in TI/FM heterostructures in fully epitaxial topological spintronic devices.
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Affiliation(s)
- Connie H Li
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
| | - Jisoo Moon
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
- National Research Council, Washington, DC 20001, United States
| | - Olaf M J van 't Erve
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
| | - Darshana Wickramaratne
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
| | - Enrique D Cobas
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
| | - Michelle D Johannes
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
| | - Berend T Jonker
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375, United States
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7
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Ngabonziza P. Quantum transport and potential of topological states for thermoelectricity in Bi 2Te 3thin films. NANOTECHNOLOGY 2022; 33:192001. [PMID: 35081521 DOI: 10.1088/1361-6528/ac4f17] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
This paper reviews recent developments in quantum transport and it presents current efforts to explore the contribution of topological insulator boundary states to thermoelectricity in Bi2Te3thin films. Although Bi2Te3has been used as a thermoelectric material for many years, it is only recently that thin films of this material have been synthesized as 3D topological insulators with interesting physics and potential applications related to topologically protected surface states. A major bottleneck in Bi2Te3thin films has been eliminating its bulk conductivity while increasing its crystal quality. The ability to grow epitaxial films with high crystal quality and to fabricate sophisticated Bi2Te3-based devices is attractive for implementing a variety of topological quantum devices and exploring the potential of topological states to improve thermoelectric properties. Special emphasis is laid on preparing low-defect-density Bi2Te3epitaxial films, gate-tuning of normal-state transport and Josephson supercurrent in topological insulator/superconductor hybrid devices. Prospective quantum transport experiments on Bi2Te3thin-film devices are discussed as well. Finally, an overview of current progress on the contribution of topological insulator boundary states to thermoelectricity is presented. Future explorations to reveal the potential of topological states for improving thermoelectric properties of Bi2Te3films and realizing high-performance thermoelectric devices are discussed.
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Affiliation(s)
- Prosper Ngabonziza
- Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany
- Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa
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8
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Liu J, Hesjedal T. Magnetic Topological Insulator Heterostructures: A Review. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021:e2102427. [PMID: 34665482 DOI: 10.1002/adma.202102427] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 06/05/2021] [Indexed: 06/13/2023]
Abstract
Topological insulators (TIs) provide intriguing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. The combination of topological properties and magnetic order can lead to new quantum states including the quantum anomalous Hall effect that was first experimentally realized in Cr-doped (Bi,Sb)2 Te3 films. Since magnetic doping can introduce detrimental effects, requiring very low operational temperatures, alternative approaches are explored. Proximity coupling to magnetically ordered systems is an obvious option, with the prospect to raise the temperature for observing the various quantum effects. Here, an overview of proximity coupling and interfacial effects in TI heterostructures is presented, which provides a versatile materials platform for tuning the magnetic and topological properties of these exciting materials. An introduction is first given to the heterostructure growth by molecular beam epitaxy and suitable structural, electronic, and magnetic characterization techniques. Going beyond transition-metal-doped and undoped TI heterostructures, examples of heterostructures are discussed, including rare-earth-doped TIs, magnetic insulators, and antiferromagnets, which lead to exotic phenomena such as skyrmions and exchange bias. Finally, an outlook on novel heterostructures such as intrinsic magnetic TIs and systems including 2D materials is given.
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Affiliation(s)
- Jieyi Liu
- Clarendon Laboratory, Department of Physics University of Oxford, Parks Road, Oxford, OX1 3PU, UK
| | - Thorsten Hesjedal
- Clarendon Laboratory, Department of Physics University of Oxford, Parks Road, Oxford, OX1 3PU, UK
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9
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Zaytseva YS, Borgardt NI, Prikhodko AS, Zallo E, Calarko R. Electron Microscopy Study of Surface Islands in Epitaxial Ge3Sb2Te6 Layer Grown on a Silicon Substrate. CRYSTALLOGR REP+ 2021. [DOI: 10.1134/s1063774521030317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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2D Bi 2Se 3 van der Waals Epitaxy on Mica for Optoelectronics Applications. NANOMATERIALS 2020; 10:nano10091653. [PMID: 32842700 PMCID: PMC7558585 DOI: 10.3390/nano10091653] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 08/06/2020] [Accepted: 08/14/2020] [Indexed: 11/27/2022]
Abstract
Bi2Se3 possesses a two-dimensional layered rhombohedral crystal structure, where the quintuple layers (QLs) are covalently bonded within the layers but weakly held together by van der Waals forces between the adjacent QLs. It is also pointed out that Bi2Se3 is a topological insulator, making it a promising candidate for a wide range of electronic and optoelectronic applications. In this study, we investigate the growth of high-quality Bi2Se3 thin films on mica by the molecular beam epitaxy technique. The films exhibited a layered structure and highly c-axis-preferred growth orientation with an XRD rocking curve full-width at half-maximum (FWHM) of 0.088°, clearly demonstrating excellent crystallinity for the Bi2Se3 deposited on the mica substrate. The growth mechanism was studied by using an interface model associated with the coincidence site lattice unit (CSLU) developed for van der Waals epitaxies. This high (001) texture favors electron transport in the material. Hall measurements revealed a mobility of 726 cm2/(Vs) at room temperature and up to 1469 cm2/(Vs) at 12 K. The results illustrate excellent electron mobility arising from the superior crystallinity of the films with significant implications for applications in conducting electrodes in optoelectronic devices on flexible substrates.
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11
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Effect of graphene substrate type on formation of Bi 2Se 3 nanoplates. Sci Rep 2019; 9:4791. [PMID: 30886194 PMCID: PMC6423328 DOI: 10.1038/s41598-019-41178-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 02/14/2019] [Indexed: 11/15/2022] Open
Abstract
Knowledge of nucleation and further growth of Bi2Se3 nanoplates on different substrates is crucial for obtaining ultrathin nanostructures and films of this material by physical vapour deposition technique. In this work, Bi2Se3 nanoplates were deposited under the same experimental conditions on different types of graphene substrates (as-transferred and post-annealed chemical vapour deposition grown monolayer graphene, monolayer graphene grown on silicon carbide substrate). Dimensions of the nanoplates deposited on graphene substrates were compared with the dimensions of the nanoplates deposited on mechanically exfoliated mica and highly ordered pyrolytic graphite flakes used as reference substrates. The influence of different graphene substrates on nucleation and further lateral and vertical growth of the Bi2Se3 nanoplates is analysed. Possibility to obtain ultrathin Bi2Se3 thin films on these substrates is evaluated. Between the substrates considered in this work, graphene grown on silicon carbide is found to be the most promising substrate for obtaining of 1–5 nm thick Bi2Se3 films.
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12
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Nanoindentation of Bi₂Se₃ Thin Films. MICROMACHINES 2018; 9:mi9100518. [PMID: 30424451 PMCID: PMC6215124 DOI: 10.3390/mi9100518] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 10/06/2018] [Accepted: 10/12/2018] [Indexed: 11/17/2022]
Abstract
The nanomechanical properties and nanoindentation responses of bismuth selenide (Bi2Se3) thin films are investigated in this study. The Bi2Se3 thin films are deposited on c-plane sapphire substrates using pulsed laser deposition. The microstructural properties of Bi2Se3 thin films are analyzed by means of X-ray diffraction (XRD). The XRD results indicated that Bi2Se3 thin films are exhibited the hexagonal crystal structure with a c-axis preferred growth orientation. Nanoindentation results showed the multiple “pop-ins” displayed in the loading segments of the load-displacement curves, suggesting that the deformation mechanisms in the hexagonal-structured Bi2Se3 films might have been governed by the nucleation and propagation of dislocations. Further, an energetic estimation of nanoindentation-induced dislocation associated with the observed pop-in effects was made using the classical dislocation theory.
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13
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Olson IA, Shtukenberg AG, Kahr B, Ward MD. Dislocations in molecular crystals. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:096501. [PMID: 30059351 DOI: 10.1088/1361-6633/aac303] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Dislocations in molecular crystals remain terra incognita. Owing to the complexity of molecular structure, dislocations in molecular crystals can be difficult to understand using only the foundational concepts devised over decades for hard materials. Herein, we review the generation, structure, and physicochemical consequences of dislocations in molecular crystals. Unlike metals, ceramics, and semiconductors, molecular crystals are often characterized by flexible building units of low symmetry, thereby limiting analysis, complicating modeling, and prompting new approaches to elucidate their role in crystallography from growth to mechanics. Such considerations affect applications ranging from plastic electronics and mechanical actuators to the tableting of pharmaceuticals.
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Affiliation(s)
- Isabel A Olson
- Department of Chemistry and Molecular Design Institute, New York University, New York City, NY 10003, United States of America
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14
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He QL, Yin G, Grutter AJ, Pan L, Che X, Yu G, Gilbert DA, Disseler SM, Liu Y, Shafer P, Zhang B, Wu Y, Kirby BJ, Arenholz E, Lake RK, Han X, Wang KL. Exchange-biasing topological charges by antiferromagnetism. Nat Commun 2018; 9:2767. [PMID: 30018306 PMCID: PMC6050290 DOI: 10.1038/s41467-018-05166-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 05/29/2018] [Indexed: 11/19/2022] Open
Abstract
Geometric Hall effect is induced by the emergent gauge field experienced by the carriers adiabatically passing through certain real-space topological spin textures, which is a probe to non-trivial spin textures, such as magnetic skyrmions. We report experimental indications of spin-texture topological charges induced in heterostructures of a topological insulator (Bi,Sb)2Te3 coupled to an antiferromagnet MnTe. Through a seeding effect, the pinned spins at the interface leads to a tunable modification of the averaged real-space topological charge. This effect experimentally manifests as a modification of the field-dependent geometric Hall effect when the system is field-cooled along different directions. This heterostructure represents a platform for manipulating magnetic topological transitions using antiferromagnetic order.
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Affiliation(s)
- Qing Lin He
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA.
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China.
| | - Gen Yin
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Alexander J Grutter
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA
| | - Lei Pan
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Xiaoyu Che
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Guoqiang Yu
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Dustin A Gilbert
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA
| | - Steven M Disseler
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA
| | - Yizhou Liu
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521-0204, USA
| | - Padraic Shafer
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Bin Zhang
- Beijing Key Lab of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Yingying Wu
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Brian J Kirby
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA
| | - Elke Arenholz
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Roger K Lake
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521-0204, USA
| | - Xiaodong Han
- Beijing Key Lab of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Kang L Wang
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA.
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15
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Li CH, van 't Erve OMJ, Yan C, Li L, Jonker BT. Electrical Detection of Charge-to-spin and Spin-to-Charge Conversion in a Topological Insulator Bi 2Te 3 Using BN/Al 2O 3 Hybrid Tunnel Barrier. Sci Rep 2018; 8:10265. [PMID: 29980749 PMCID: PMC6035191 DOI: 10.1038/s41598-018-28547-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Accepted: 06/18/2018] [Indexed: 11/18/2022] Open
Abstract
One of the most striking properties of three-dimensional topological insulators (TIs) is spin-momentum locking, where the spin is locked at right angles to momentum and hence an unpolarized charge current creates a net spin polarization. Alternatively, if a net spin is injected into the TI surface state system, it is distinctively associated with a unique carrier momentum and hence should generate a charge accumulation, as in the so-called inverse Edelstein effect. Here using a Fe/Al2O3/BN tunnel barrier, we demonstrate both effects in a single device in Bi2Te3: the electrical detection of the spin accumulation generated by an unpolarized current flowing through the surface states, and that of the charge accumulation generated by spins injected into the surface state system. This work is the first to utilize BN as part of a hybrid tunnel barrier on TI, where we observed a high spin polarization of 93% for the TI surfaces states. The reverse spin-to-charge measurement is an independent confirmation that spin and momentum are locked in the surface states of TI, and offers additional avenues for spin manipulation. It further demonstrates the robustness and versatility of electrical access to the spin system within TI surface states, an important step towards its utilization in TI-based spintronics devices.
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Affiliation(s)
- C H Li
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC, 20375, USA.
| | - O M J van 't Erve
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC, 20375, USA
| | - C Yan
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV, 26506, USA
| | - L Li
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV, 26506, USA
| | - B T Jonker
- Materials Science and Technology Division, Naval Research Laboratory, Washington, DC, 20375, USA
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16
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Yan C, Dong X, Li CH, Li L. Charging effect at grain boundaries of MoS 2. NANOTECHNOLOGY 2018; 29:195704. [PMID: 29400312 DOI: 10.1088/1361-6528/aaace9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Grain boundaries (GBs) are inherent extended defects in chemical vapor deposited (CVD) transition metal dichalcogenide (TMD) films. Characterization of the atomic structure and electronic properties of these GBs is crucial for understanding and controlling the properties of TMDs via defect engineering. Here, we report the atomic and electronic structure of GBs in CVD grown MoS2 on epitaxial graphene/SiC(0001). Using scanning tunneling microscopy/spectroscopy, we find that GBs mostly consist of arrays of dislocation cores, where the presence of mid-gap states shifts both conduction and valence band edges by up to 1 eV. Our findings demonstrate the first charging effect near GBs in CVD grown MoS2, providing insights into the significant impact GBs can have on materials properties.
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Affiliation(s)
- Chenhui Yan
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, United States of America
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17
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Hull R, Keblinski P, Lewis D, Maniatty A, Meunier V, Oberai AA, Picu CR, Samuel J, Shephard MS, Tomozawa M, Vashishth D, Zhang S. Stochasticity in materials structure, properties, and processing-A review. APPLIED PHYSICS REVIEWS 2018; 5:011302. [PMID: 30397419 PMCID: PMC6214486 DOI: 10.1063/1.4998144] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We review the concept of stochasticity-i.e., unpredictable or uncontrolled fluctuations in structure, chemistry, or kinetic processes-in materials. We first define six broad classes of stochasticity: equilibrium (thermodynamic) fluctuations; structural/compositional fluctuations; kinetic fluctuations; frustration and degeneracy; imprecision in measurements; and stochasticity in modeling and simulation. In this review, we focus on the first four classes that are inherent to materials phenomena. We next develop a mathematical framework for describing materials stochasticity and then show how it can be broadly applied to these four materials-related stochastic classes. In subsequent sections, we describe structural and compositional fluctuations at small length scales that modify material properties and behavior at larger length scales; systems with engineered fluctuations, concentrating primarily on composite materials; systems in which stochasticity is developed through nucleation and kinetic phenomena; and configurations in which constraints in a given system prevent it from attaining its ground state and cause it to attain several, equally likely (degenerate) states. We next describe how stochasticity in these processes results in variations in physical properties and how these variations are then accentuated by-or amplify-stochasticity in processing and manufacturing procedures. In summary, the origins of materials stochasticity, the degree to which it can be predicted and/or controlled, and the possibility of using stochastic descriptions of materials structure, properties, and processing as a new degree of freedom in materials design are described.
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Affiliation(s)
- Robert Hull
- Department of Materials Science and Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Pawel Keblinski
- Department of Materials Science and Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Dan Lewis
- Department of Materials Science and Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Antoinette Maniatty
- Department of Mechanical, Aeronautical and Nuclear Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Vincent Meunier
- Department of Physics, Applied Physics, and Astronomy & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Assad A Oberai
- Department of Mechanical, Aeronautical and Nuclear Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Catalin R Picu
- Department of Mechanical, Aeronautical and Nuclear Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Johnson Samuel
- Department of Mechanical, Aeronautical and Nuclear Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Mark S Shephard
- Department of Mechanical, Aeronautical and Nuclear Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Minoru Tomozawa
- Department of Materials Science and Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Deepak Vashishth
- Department of Biomedical Engineering & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
| | - Shengbai Zhang
- Department of Physics, Applied Physics, and Astronomy & Center for Materials, Devices and Integrated Systems, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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18
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Charpentier S, Galletti L, Kunakova G, Arpaia R, Song Y, Baghdadi R, Wang SM, Kalaboukhov A, Olsson E, Tafuri F, Golubev D, Linder J, Bauch T, Lombardi F. Induced unconventional superconductivity on the surface states of Bi 2Te 3 topological insulator. Nat Commun 2017; 8:2019. [PMID: 29222507 PMCID: PMC5722924 DOI: 10.1038/s41467-017-02069-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Accepted: 11/05/2017] [Indexed: 11/09/2022] Open
Abstract
Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p x + ip y wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral p x + ip y component. The magnetic field pattern of the junctions shows a dip at zero externally applied magnetic field, which is an incontrovertible signature of the simultaneous existence of 0 and π coupling within the junction, inherent to a non trivial order parameter phase. The nano-textured morphology of the Bi2Te3 flakes, and the dramatic role played by thermal strain are the surprising key factors for the display of an unconventional induced order parameter.
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Affiliation(s)
- Sophie Charpentier
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Luca Galletti
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Gunta Kunakova
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
- Institute of Chemical Physics, University of Latvia, 19 Raina Boulevard, LV-1586, Riga, Latvia
| | - Riccardo Arpaia
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Yuxin Song
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai, CN-200050, China
| | - Reza Baghdadi
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Shu Min Wang
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai, CN-200050, China
| | - Alexei Kalaboukhov
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Eva Olsson
- Department of Applied Physics, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Francesco Tafuri
- Dipartimento di Fisica E. Pancini, Università di Napoli Federico II, IT-80126, Napoli, Italy
- CNR-SPIN Institute of Superconductors, Innovative Materials and Devices, Napoli, IT-80125, Italy
| | - Dmitry Golubev
- Department of Applied Physics, Aalto University School of Science, P.O. Box 13500, FI-00076, Aalto, Finland
| | - Jacob Linder
- Department of Physics, QuSpin Center of Excellence, Norwegian University of Science and Technology, N-7491, Trondheim, Norway
| | - Thilo Bauch
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - Floriana Lombardi
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden.
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19
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Tayal A, Kumar D, Lakhani A. Role of lattice inhomogeneities on the electronic properties of selenium deficient Bi 2Se 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:445704. [PMID: 28850048 DOI: 10.1088/1361-648x/aa88f5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Inter-layer coupling is widely considered to play a crucial role in tuning electronic properties of 3D topological insulators. The aim of this study is to evaluate the role of crystallographic defects on inter-layer coupling in the Se deficient Bi2Se3 (0 0 3) crystal using extended x-ray absorption fine structure spectroscopy (EXAFS) technique. EXAFS measurements at Se-K and Bi-L3 edges reveal distinct local geometry around these atomic sites. It has been observed that short inter-layer Bi-Se and Se-Se bonds emerge in the sample. This additional structural motif coexists with the conventional crystallographic arrangement. Within the quintuple layer Bi-Se bonds are preserved with slight compression in intra-planer Bi-Bi and Se-Se distance and overall reduction in c/a ratio. These findings suggest formation of deformed lattice region, localized and dispersed inhomogeneously within the sample. Such inhomogeneities have also resulted in interesting transport properties such as quantum Hall effect (QHE), large linear magnetoresistance and π-Berry phase in Shubnikov-de Haas (SdH) oscillations of bulk crystals. Detailed analyses of magnetotransport measurements suggest that tuning of inter-layer coupling by local lattice deformation is the key factor for unusual transport properties. Role of axial strain, and stacking faults generated due to defects and charged Se vacancies are discussed to understand the observed electronic properties.
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Affiliation(s)
- Akhil Tayal
- Ligne MARS, Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin -BP 48 91192 Gif-sur-Yvette cedex, France
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20
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Direct comparison of current-induced spin polarization in topological insulator Bi 2Se 3 and InAs Rashba states. Nat Commun 2016; 7:13518. [PMID: 27853143 PMCID: PMC5118552 DOI: 10.1038/ncomms13518] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 10/11/2016] [Indexed: 01/27/2023] Open
Abstract
Three-dimensional topological insulators (TIs) exhibit time-reversal symmetry protected, linearly dispersing Dirac surface states with spin–momentum locking. Band bending at the TI surface may also lead to coexisting trivial two-dimensional electron gas (2DEG) states with parabolic energy dispersion. A bias current is expected to generate spin polarization in both systems, although with different magnitude and sign. Here we compare spin potentiometric measurements of bias current-generated spin polarization in Bi2Se3(111) where Dirac surface states coexist with trivial 2DEG states, and in InAs(001) where only trivial 2DEG states are present. We observe spin polarization arising from spin–momentum locking in both cases, with opposite signs of the measured spin voltage. We present a model based on spin dependent electrochemical potentials to directly derive the sign expected for the Dirac surface states, and show that the dominant contribution to the current-generated spin polarization in the TI is from the Dirac surface states. Spin-polarized states arising from either Rashba splitting or topological effects are expected to produce current-induced spin polarization with different magnitude and sign. Here, Li et al. observe current-generated spin polarization in both Bi2Se3 (111) and InAs (001) films, with opposite signs of the spin voltage.
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21
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Rajput S, Li YY, Weinert M, Li L. Indirect Interlayer Bonding in Graphene-Topological Insulator van der Waals Heterostructure: Giant Spin-Orbit Splitting of the Graphene Dirac States. ACS NANO 2016; 10:8450-8456. [PMID: 27617796 DOI: 10.1021/acsnano.6b03387] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
van der Waals (vdW) heterostructures of two-dimensional materials exhibit properties and functionalities that can be tuned by stacking order and interlayer coupling. Although direct covalent bonding is not expected at the heterojunction, the formation of an interface nevertheless breaks the symmetries of the layers, and the orthogonal requirement of the wave functions can lead to indirect interfacial coupling, creating new properties and functionalities beyond their constituent layers. Here, we fabricate graphene/topological insulator vdW heterostructure by transferring chemical vapor deposited graphene onto Bi2Se3 grown by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we observe a giant spin-orbit splitting of the graphene Dirac states up to 80 meV. Density functional theory calculations further reveal that this splitting of the graphene bands is a consequence of the breaking of inversion symmetry and the orthogonalization requirement on the overlapping wave functions at the interface, rather than simple direct bonding. Our findings reveal two intrinsic characteristics-the symmetry breaking and orthogonalization of the wave functions at the interface-that underlines the properties of vdW heterostructures.
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Affiliation(s)
- Shivani Rajput
- Department of Physics, University of Wisconsin , Milwaukee, Wisconsin 53211, United States
| | - Yao-Yi Li
- Department of Physics, University of Wisconsin , Milwaukee, Wisconsin 53211, United States
| | - Michael Weinert
- Department of Physics, University of Wisconsin , Milwaukee, Wisconsin 53211, United States
| | - Lian Li
- Department of Physics, University of Wisconsin , Milwaukee, Wisconsin 53211, United States
- Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506, United States
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22
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Kim KC, Lee J, Kim BK, Choi WY, Chang HJ, Won SO, Kwon B, Kim SK, Hyun DB, Kim HJ, Koo HC, Choi JH, Kim DI, Kim JS, Baek SH. Free-electron creation at the 60° twin boundary in Bi2Te3. Nat Commun 2016; 7:12449. [PMID: 27527268 PMCID: PMC4990697 DOI: 10.1038/ncomms12449] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 07/05/2016] [Indexed: 12/03/2022] Open
Abstract
Interfaces, such as grain boundaries in a solid material, are excellent regions to explore novel properties that emerge as the result of local symmetry-breaking. For instance, at the interface of a layered-chalcogenide material, the potential reconfiguration of the atoms at the boundaries can lead to a significant modification of the electronic properties because of their complex atomic bonding structure. Here, we report the experimental observation of an electron source at 60° twin boundaries in Bi2Te3, a representative layered-chalcogenide material. First-principles calculations reveal that the modification of the interatomic distance at the 60° twin boundary to accommodate structural misfits can alter the electronic structure of Bi2Te3. The change in the electronic structure generates occupied states within the original bandgap in a favourable condition to create carriers and enlarges the density-of-states near the conduction band minimum. The present work provides insight into the various transport behaviours of thermoelectrics and topological insulators. Grain boundaries in polycrystalline materials may offer the opportunity to explore physical phenomena that do not normally occur within the crystal grains. Here, the authors show that twin boundaries in Bi2Te3 works as an electron supply for the whole bulk material.
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Affiliation(s)
- Kwang-Chon Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.,School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
| | - Joohwi Lee
- Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
| | - Byung Kyu Kim
- High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Won Young Choi
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, Republic of Korea.,Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Hye Jung Chang
- Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.,Department of Nanomaterials, Korea University of Science and Technology, Daejeon 305-333, Republic of Korea
| | - Sung Ok Won
- Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Beomjin Kwon
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Seong Keun Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Dow-Bin Hyun
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Hyun Jae Kim
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
| | - Hyun Cheol Koo
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, Republic of Korea.,Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Jung-Hae Choi
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Dong-Ik Kim
- High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Jin-Sang Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
| | - Seung-Hyub Baek
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.,Department of Nanomaterials, Korea University of Science and Technology, Daejeon 305-333, Republic of Korea
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23
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Abstract
Thin film epitaxy typically invokes a superposition of a pair of rigid two-dimensional lattices with a well-defined orientation governed by some form of commensurism. A report by Meissner et al. in this issue of ACS Nano demonstrates that the organization of organic molecules on substrates may not be that simple, as static distortion waves involving miniscule shifts of atomic positions from substrate lattice points can lead to orientations of a molecular film that cannot be described by often used models. Herein, we provide some highlights of epitaxy, with a focus on configurations that reflect the delicate balance between intermolecular interactions within a molecular film and molecule-substrate interactions. Although geometric models for explaining and predicting epitaxial configurations can be used to guide synthesis of materials, their use must recognize energetic factors and the possibility of more complex, and possibly less predictable, interface structures.
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Affiliation(s)
- Michael D Ward
- Department of Chemistry and the Molecular Design Institute, New York University , 100 Washington Square East, New York, New York 10003-6688, United States
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24
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Huang WK, Zhang KW, Yang CL, Ding H, Wan X, Li SC, Evans JW, Han Y. Tailoring Kinetics on a Topological Insulator Surface by Defect-Induced Strain: Pb Mobility on Bi2Te3. NANO LETTERS 2016; 16:4454-4461. [PMID: 27302741 DOI: 10.1021/acs.nanolett.6b01604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Heteroepitaxial structures based on Bi2Te3-type topological insulators (TIs) exhibit exotic quantum phenomena. For optimal characterization of these phenomena, it is desirable to control the interface structure during film growth on such TIs. In this process, adatom mobility is a key factor. We demonstrate that Pb mobility on the Bi2Te3(111) surface can be modified by the engineering local strain, ε, which is induced around the point-like defects intrinsically forming in the Bi2Te3(111) thin film grown on a Si(111)-7 × 7 substrate. Scanning tunneling microscopy observations of Pb adatom and cluster distributions and first-principles density functional theory (DFT) analyses of the adsorption energy and diffusion barrier Ed of Pb adatom on Bi2Te3(111) surface show a significant influence of ε. Surprisingly, Ed reveals a cusp-like dependence on ε due to a bifurcation in the position of the stable adsorption site at the critical tensile strain εc ≈ 0.8%. This constitutes a very different strain-dependence of diffusivity from all previous studies focusing on conventional metal or semiconductor surfaces. Kinetic Monte Carlo simulations of Pb deposition, diffusion, and irreversible aggregation incorporating the DFT results reveal adatom and cluster distributions compatible with our experimental observations.
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Affiliation(s)
- Wen-Kai Huang
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
| | - Kai-Wen Zhang
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
| | - Chao-Long Yang
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
| | - Haifeng Ding
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, P. R. China
| | - Xiangang Wan
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, P. R. China
| | - Shao-Chun Li
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University , Nanjing 210093, P. R. China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, P. R. China
| | - James W Evans
- Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States
- Ames Laboratory- U.S. Department of Energy, Iowa State University , Ames, Iowa 50011, United States
| | - Yong Han
- Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States
- Ames Laboratory- U.S. Department of Energy, Iowa State University , Ames, Iowa 50011, United States
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25
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Electrical Detection of the Helical Spin Texture in a p-type Topological Insulator Sb2Te3. Sci Rep 2016; 6:29533. [PMID: 27404321 PMCID: PMC4941728 DOI: 10.1038/srep29533] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 06/17/2016] [Indexed: 01/27/2023] Open
Abstract
The surface states of 3D topological insulators (TIs) exhibit a helical spin texture with spin locked at right angles with momentum. The chirality of this spin texture is expected to invert crossing the Dirac point, a property that has been experimentally observed by optical probes. Here, we directly determine the chirality below the Dirac point by electrically detecting spin-momentum locking in surface states of a p-type TI, Sb2Te3. A current flowing in the Sb2Te3 surface states generates a net spin polarization due to spin-momentum locking, which is electrically detected as a voltage on an Fe/Al2O3 tunnel barrier detector. Measurements of this voltage as a function of current direction and detector magnetization indicate that hole spin-momentum locking follows the right-hand rule, opposite that of electron, providing direct confirmation that the chirality is indeed inverted below Dirac point. The spin signal is linear with current, and exhibits a temperature dependence consistent with the semiconducting nature of the TI film and freeze-out of bulk conduction below 100 K. Our results demonstrate that the chirality of the helical spin texture of TI surface states can be determined electrically, an enabling step in the electrical manipulation of spins in next generation TI-based quantum devices.
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Zhang L, Yan Y, Wu HC, Yu D, Liao ZM. Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions. ACS NANO 2016; 10:3816-3822. [PMID: 26930548 DOI: 10.1021/acsnano.6b00659] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Graphene-based vertical heterostructures, particularly stacks incorporated with other layered materials, are promising for nanoelectronics. The stacking of two model Dirac materials, graphene and topological insulator, can considerably enlarge the family of van der Waals heterostructures. Despite good understanding of the two individual materials, the electron transport properties of a combined vertical heterojunction are still unknown. Here, we show the experimental realization of a vertical heterojunction between Bi2Se3 nanoplate and monolayer graphene. At low temperatures, the electron transport through the vertical heterojunction is dominated by the tunneling process, which can be effectively tuned by gate voltage to alter the density of states near the Fermi surface. In the presence of a magnetic field, quantum oscillations are observed due to the quantized Landau levels in both graphene and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an exotic gate-tunable tunneling resistance under high magnetic field, which displays resistance maxima when the underlying graphene becomes a quantum Hall insulator.
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Affiliation(s)
- Liang Zhang
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University , Beijing 100871, P.R. China
| | - Yuan Yan
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University , Beijing 100871, P.R. China
| | - Han-Chun Wu
- School of Physics, Beijing Institute of Technology , Beijing 100081, P.R. China
| | - Dapeng Yu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University , Beijing 100871, P.R. China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University , Beijing 100871, P.R. China
| | - Zhi-Min Liao
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University , Beijing 100871, P.R. China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871, China
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Das B, Sarkar S, Khan R, Santra S, Das NS, Chattopadhyay KK. rGO-Wrapped flowerlike Bi2Se3 nanocomposite: synthesis, experimental and simulation-based investigation on cold cathode applications. RSC Adv 2016. [DOI: 10.1039/c5ra28064h] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Bi2Se3 nanoflowers (NFs) – reduced graphene oxide (rGO) nanocomposite (BG) synthesized via cost-effective, ecofriendly and easy hydrothermal route: smart cold cathode for future display device.
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Affiliation(s)
- Biswajit Das
- School of Materials Science & Nanotechnology
- Jadavpur University
- Kolkata 700 032
- India
| | - Samrat Sarkar
- School of Materials Science & Nanotechnology
- Jadavpur University
- Kolkata 700 032
- India
| | - Rimpa Khan
- School of Materials Science & Nanotechnology
- Jadavpur University
- Kolkata 700 032
- India
| | - Saswati Santra
- Thin Film & Nanoscience Laboratory
- Department of Physics
- Jadavpur University
- Kolkata 700 032
- India
| | - Nirmalya Sankar Das
- School of Materials Science & Nanotechnology
- Jadavpur University
- Kolkata 700 032
- India
| | - Kalyan Kumar Chattopadhyay
- School of Materials Science & Nanotechnology
- Jadavpur University
- Kolkata 700 032
- India
- Thin Film & Nanoscience Laboratory
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Guo Y, Liu Z, Peng H. A Roadmap for Controlled Production of Topological Insulator Nanostructures and Thin Films. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:3290-3305. [PMID: 25727694 DOI: 10.1002/smll.201403426] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Revised: 01/14/2015] [Indexed: 06/04/2023]
Abstract
The group V-VI chalcogenide semiconductors (Bi2 Se3 , Bi2 Te3 , and Sb2 Te3 ) have long been known as thermoelectric materials. Recently, they have been once more generating interest because Bi2 Se3 , Bi2 Te3 and Sb2 Te3 have been crowned as 3D topological insulators (TIs), which have insulating bulk gaps and metallic Dirac surface states. One big challenge in the study of TIs is the lack of high-quality materials with few defects and insulating bulk states. To manifest the topological surface states, it is critical to suppress the contribution from the bulk carriers. Controlled production of TI nanostructures that have a large surface-to-volume ratio is an efficient way to reduce the bulk conductance and to significantly enhance the topological surface conduction. In this review article, the recent progress on the preparation of TI nanostructures is highlighted. Basic production methods for TI nanostructures are introduced in detail. Furthermore, several specific production approaches to reduce the residual bulk carriers from defects are summarized. Finally, the progress and the prospects of the production of TI-based heterostructures, which hold promise in both fundamental study and novel applications are discussed.
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Affiliation(s)
- Yunfan Guo
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P.R. China
| | - Zhongfan Liu
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P.R. China
| | - Hailin Peng
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P.R. China
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Li CH, van 't Erve OMJ, Robinson JT, Liu Y, Li L, Jonker BT. Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3. NATURE NANOTECHNOLOGY 2014; 9:218-224. [PMID: 24561354 DOI: 10.1038/nnano.2014.16] [Citation(s) in RCA: 132] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 01/17/2014] [Indexed: 06/03/2023]
Abstract
Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators' surface-state spin system and enable utilization of its remarkable properties for future technological applications.
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Affiliation(s)
- C H Li
- Materials Science and Technology Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - O M J van 't Erve
- Materials Science and Technology Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - J T Robinson
- Electronics Science and Technology Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - Y Liu
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53211, USA
| | - L Li
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53211, USA
| | - B T Jonker
- Materials Science and Technology Division, Naval Research Laboratory, Washington, District of Columbia 20375, USA
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Kim N, Lee P, Kim Y, Kim JS, Kim Y, Noh DY, Yu SU, Chung J, Kim KS. Persistent topological surface state at the interface of Bi2Se3 film grown on patterned graphene. ACS NANO 2014; 8:1154-60. [PMID: 24437450 DOI: 10.1021/nn405503k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We employed graphene as a patternable template to protect the intrinsic surface states of thin films of topological insulators (TIs) from environment. Here we find that the graphene provides high-quality interface so that the Shubnikov de Haas (SdH) oscillation associated with a topological surface state could be observed at the interface of a metallic Bi2Se3 film with a carrier density higher than ∼ 10(19) cm(-3). Our in situ X-ray diffraction study shows that the Bi2Se3 film grows epitaxially in a quintuple layer-by-layer fashion from the bottom layer without any structural distortion by interfacial strain. The magnetotransport measurements including SdH oscillations stemming from multiple conductance channels reveal that the topological surface state, with the mobility as high as ∼ 0.5 m(2)/(V s), remains intact from the graphene underneath without degradation. Given that the graphene was prepatterned on arbitrary insulating substrates, the TI-based microelectronic design could be exploited. Our study thus provides a step forward to observe the topological surface states at the interface without degradation by tuning the interface between TI and graphene into a measurable current for device application.
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Affiliation(s)
- Namdong Kim
- Department of Chemistry, ‡Department of Physics, §Pohang Accelerator Laboratory, Pohang University of Science and Technology , Pohang 790-784, Korea
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Kandala A, Richardella A, Zhang D, Flanagan TC, Samarth N. Surface-sensitive two-dimensional magneto-fingerprint in mesoscopic Bi2Se3 channels. NANO LETTERS 2013; 13:2471-2476. [PMID: 23642037 DOI: 10.1021/nl4012358] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Periodic Aharonov–Bohm and Altshuler–Aronov–Spivak oscillations have traditionally been observed in lateral transport through patterned mesoscopic loops of diffusive conductors. However, our studies of perpendicular-to-plane magnetotransport in straight-channel, diffusive devices of epitaxial Bi2Se3 surprisingly reveal signatures of Aharonov–Bohm orbits, periodic conductance fluctuation magneto-fingerprints, even though the devices are not explicitly patterned into loops. We show that the length scale of these orbits corresponds to the typical perimeter of triangular terraces found on the surface of these thin film devices, strongly suggesting that the periodic magneto-fingerprint arises from coherent scattering of electron waves from the step-edges. Our interpretation is bolstered by control measurements in devices without such surface morphology that only show a conventional, aperiodic magneto-fingerprint. These results show that lithographically patterned Bi2Se3 devices provide a novel class of mesoscopic physical systems for systematic studies of coherent surface sensitive transport.
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Affiliation(s)
- Abhinav Kandala
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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Utama MIB, Zhang Q, Zhang J, Yuan Y, Belarre FJ, Arbiol J, Xiong Q. Recent developments and future directions in the growth of nanostructures by van der Waals epitaxy. NANOSCALE 2013; 5:3570-3588. [PMID: 23508233 DOI: 10.1039/c3nr34011b] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Here we review the characteristics of "van der Waals epitaxy" (vdWE) as an alternative epitaxy mechanism that has been demonstrated as a viable method for circumventing the lattice matching requirements for epitaxial growth. Particular focus is given on the application of vdWE for nonplanar nanostructures. We highlight our works on the vdWE growth of nanowire arrays, tripods, and tetrapods from various semiconductors (ZnO, ZnTe, CdS, CdSe, CdSxSe1-x, CdTe, and PbS) on muscovite mica substrates, irrespective of the ensuing lattice mismatch. We then address the controllability of the synthesis and the growth mechanism of ZnO nanowires from catalyst-free vdWE in vapor transport growth. As exemplified herein with optical characterizations of ZnO and CdSe nanowires, we show that samples from vdWE may possess properties that are as excellent as those from conventional epitaxy. With our works, we aim to advocate vdWE as a prospective universal growth strategy for nonplanar epitaxial nanostructures.
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Affiliation(s)
- Muhammad Iqbal Bakti Utama
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
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Liu Y, Li YY, Gilks D, Lazarov VK, Weinert M, Li L. Charging Dirac states at antiphase domain boundaries in the three-dimensional topological insulator Bi2Se3. PHYSICAL REVIEW LETTERS 2013; 110:186804. [PMID: 23683233 DOI: 10.1103/physrevlett.110.186804] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Indexed: 06/02/2023]
Abstract
Using scanning tunneling microscopy and transmission electron microscopy, we demonstrate the existence of antiphase boundaries between neighboring grains shifted by a fraction of a quintuple layer in epitaxial (0001) films of the three-dimensional topological insulator Bi(2)Se(3). Scanning tunneling spectroscopy and first-principles calculations reveal that these antiphase boundaries provide electrostatic fields on the order of 10(8) V/m that locally charge the Dirac states, modulating the carrier density, and shift the Dirac point by up to 120 meV. This intrinsic electric field effect, demonstrated here near interfaces between Bi(2)Se(3) grains, provides direct experimental evidence at the atomic scale that the Dirac states are indeed robust against extended structural defects and tunable by electric field. These results also shed light on the recent observation of coexistence of Dirac states and two-dimensional electron gas on Bi(2)Se(3) (0001) after adsorption of metal atoms and gas molecules.
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Affiliation(s)
- Y Liu
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53211, USA
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Yan Y, Liao ZM, Zhou YB, Wu HC, Bie YQ, Chen JJ, Meng J, Wu XS, Yu DP. Synthesis and quantum transport properties of Bi₂Se₃ topological insulator nanostructures. Sci Rep 2013; 3:1264. [PMID: 23405278 PMCID: PMC3569629 DOI: 10.1038/srep01264] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 01/14/2013] [Indexed: 11/10/2022] Open
Abstract
Bi2Se3 nanocrystals with various morphologies, including nanotower, nanoplate, nanoflake, nanobeam and nanowire, have been synthesized. Well-distinguished Shubnikov-de Haas (SdH) oscillations were observed in Bi2Se3 nanoplates and nanobeams. Careful analysis of the SdH oscillations suggests the existence of Berry's phase π, which confirms the quantum transport of the surface Dirac fermions in both Bi2Se3 nanoplates and nanobeams without intended doping. The observation of the singular quantum transport of the topological surface states implies that the high-quality Bi2Se3 nanostructures have superiorities for investigating the novel physical properties and developing the potential applications.
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Affiliation(s)
- Yuan Yan
- State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P.R. China
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