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Chen S, Lourembam J, Ho P, Toh AKJ, Huang J, Chen X, Tan HK, Yap SLK, Lim RJJ, Tan HR, Suraj TS, Sim MI, Toh YT, Lim I, Lim NCB, Zhou J, Chung HJ, Lim ST, Soumyanarayanan A. All-electrical skyrmionic magnetic tunnel junction. Nature 2024; 627:522-527. [PMID: 38509277 DOI: 10.1038/s41586-024-07131-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 01/25/2024] [Indexed: 03/22/2024]
Abstract
Topological whirls or 'textures' of spins such as magnetic skyrmions represent the smallest realizable emergent magnetic entities1-5. They hold considerable promise as robust, nanometre-scale, mobile bits for sustainable computing6-8. A longstanding roadblock to unleashing their potential is the absence of a device enabling deterministic electrical readout of individual spin textures9,10. Here we present the wafer-scale realization of a nanoscale chiral magnetic tunnel junction (MTJ) hosting a single, ambient skyrmion. Using a suite of electrical and multimodal imaging techniques, we show that the MTJ nucleates skyrmions of fixed polarity, whose large readout signal-20-70% relative to uniformly magnetized states-corresponds directly to skyrmion size. The MTJ exploits complementary nucleation mechanisms to stabilize distinctly sized skyrmions at zero field, thereby realizing three non-volatile electrical states. Crucially, it can electrically write and delete skyrmions to both uniform states with switching energies 1,000 times lower than the state of the art. Here, the applied voltage emulates a magnetic field and, in contrast to conventional MTJs, it reshapes both the energetics and kinetics of the switching transition, enabling deterministic bidirectional switching. Our stack platform enables large readout and efficient switching, and is compatible with lateral manipulation of skyrmionic bits, providing the much-anticipated backbone for all-electrical skyrmionic device architectures9,10. Its wafer-scale realizability provides a springboard to harness chiral spin textures for multibit memory and unconventional computing8,11.
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Affiliation(s)
- Shaohai Chen
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - James Lourembam
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Pin Ho
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Alexander K J Toh
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Jifei Huang
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Xiaoye Chen
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Hang Khume Tan
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Sherry L K Yap
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Royston J J Lim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Hui Ru Tan
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - T S Suraj
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - May Inn Sim
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Yeow Teck Toh
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Idayu Lim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Nelson C B Lim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Jing Zhou
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Hong Jing Chung
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Sze Ter Lim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Anjan Soumyanarayanan
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore.
- Department of Physics, National University of Singapore, Singapore, Singapore.
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Chen M, Chai J, Wu J, Zheng H, Wu WY, Lourembam J, Lin M, Kim JY, Kim J, Ang KW, Ng MF, Medina H, Tong SW, Chi D. Sublimation-based wafer-scale monolayer WS 2 formation via self-limited thinning of few-layer WS 2. Nanoscale Horiz 2023; 9:132-142. [PMID: 37850320 DOI: 10.1039/d3nh00358b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2023]
Abstract
Atomically-thin monolayer WS2 is a promising channel material for next-generation Moore's nanoelectronics owing to its high theoretical room temperature electron mobility and immunity to short channel effect. The high photoluminescence (PL) quantum yield of the monolayer WS2 also makes it highly promising for future high-performance optoelectronics. However, the difficulty in strictly growing monolayer WS2, due to its non-self-limiting growth mechanism, may hinder its industrial development because of the uncontrollable growth kinetics in attaining the high uniformity in thickness and property on the wafer-scale. In this study, we report a scalable process to achieve a 4 inch wafer-scale fully-covered strictly monolayer WS2 by applying the in situ self-limited thinning of multilayer WS2 formed by sulfurization of WOx films. Through a pulsed supply of sulfur precursor vapor under a continuous H2 flow, the self-limited thinning process can effectively trim down the overgrown multilayer WS2 to the monolayer limit without damaging the remaining bottom WS2 monolayer. Density functional theory (DFT) calculations reveal that the self-limited thinning arises from the thermodynamic instability of the WS2 top layers as opposed to a stable bottom monolayer WS2 on sapphire above a vacuum sublimation temperature of WS2. The self-limited thinning approach overcomes the intrinsic limitation of conventional vapor-based growth methods in preventing the 2nd layer WS2 domain nucleation/growth. It also offers additional advantages, such as scalability, simplicity, and possibility for batch processing, thus opening up a new avenue to develop a manufacturing-viable growth technology for the preparation of a strictly-monolayer WS2 on the wafer-scale.
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Affiliation(s)
- Mingxi Chen
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Jianwei Chai
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Jing Wu
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Haofei Zheng
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Republic of Singapore
| | - Wen-Ya Wu
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - James Lourembam
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Ming Lin
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Jun-Young Kim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Jaewon Kim
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Kah-Wee Ang
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Republic of Singapore
| | - Man-Fai Ng
- Institute of High Performance Computing (IHPC), Agency for Science, Technology and Research (A*STAR), 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Republic of Singapore
| | - Henry Medina
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Shi Wun Tong
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
| | - Dongzhi Chi
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore.
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Xin N, Lourembam J, Kumaravadivel P, Kazantsev AE, Wu Z, Mullan C, Barrier J, Geim AA, Grigorieva IV, Mishchenko A, Principi A, Fal'ko VI, Ponomarenko LA, Geim AK, Berdyugin AI. Giant magnetoresistance of Dirac plasma in high-mobility graphene. Nature 2023; 616:270-274. [PMID: 37045919 PMCID: PMC10097601 DOI: 10.1038/s41586-023-05807-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2022] [Accepted: 02/08/2023] [Indexed: 04/14/2023]
Abstract
The most recognizable feature of graphene's electronic spectrum is its Dirac point, around which interesting phenomena tend to cluster. At low temperatures, the intrinsic behaviour in this regime is often obscured by charge inhomogeneity1,2 but thermal excitations can overcome the disorder at elevated temperatures and create an electron-hole plasma of Dirac fermions. The Dirac plasma has been found to exhibit unusual properties, including quantum-critical scattering3-5 and hydrodynamic flow6-8. However, little is known about the plasma's behaviour in magnetic fields. Here we report magnetotransport in this quantum-critical regime. In low fields, the plasma exhibits giant parabolic magnetoresistivity reaching more than 100 per cent in a magnetic field of 0.1 tesla at room temperature. This is orders-of-magnitude higher than magnetoresistivity found in any other system at such temperatures. We show that this behaviour is unique to monolayer graphene, being underpinned by its massless spectrum and ultrahigh mobility, despite frequent (Planckian limit) scattering3-5,9-14. With the onset of Landau quantization in a magnetic field of a few tesla, where the electron-hole plasma resides entirely on the zeroth Landau level, giant linear magnetoresistivity emerges. It is nearly independent of temperature and can be suppressed by proximity screening15, indicating a many-body origin. Clear parallels with magnetotransport in strange metals12-14 and so-called quantum linear magnetoresistance predicted for Weyl metals16 offer an interesting opportunity to further explore relevant physics using this well defined quantum-critical two-dimensional system.
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Affiliation(s)
- Na Xin
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - James Lourembam
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - Piranavan Kumaravadivel
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - A E Kazantsev
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - Zefei Wu
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Ciaran Mullan
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - Julien Barrier
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Alexandra A Geim
- National Graphene Institute, University of Manchester, Manchester, UK
| | - I V Grigorieva
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - A Mishchenko
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - A Principi
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - V I Fal'ko
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - L A Ponomarenko
- Department of Physics, University of Lancaster, Lancaster, UK.
| | - A K Geim
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
- National Graphene Institute, University of Manchester, Manchester, UK.
- Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore.
| | - Alexey I Berdyugin
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
- National Graphene Institute, University of Manchester, Manchester, UK.
- Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore.
- Department of Physics, National University of Singapore, Singapore, Singapore.
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4
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Tan AKC, Ho P, Lourembam J, Huang L, Tan HK, Reichhardt CJO, Reichhardt C, Soumyanarayanan A. Visualizing the strongly reshaped skyrmion Hall effect in multilayer wire devices. Nat Commun 2021; 12:4252. [PMID: 34253721 PMCID: PMC8275747 DOI: 10.1038/s41467-021-24114-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 05/28/2021] [Indexed: 12/02/2022] Open
Abstract
Magnetic skyrmions are nanoscale spin textures touted as next-generation computing elements. When subjected to lateral currents, skyrmions move at considerable speeds. Their topological charge results in an additional transverse deflection known as the skyrmion Hall effect (SkHE). While promising, their dynamic phenomenology with current, skyrmion size, geometric effects and disorder remain to be established. Here we report on the ensemble dynamics of individual skyrmions forming dense arrays in Pt/Co/MgO wires by examining over 20,000 instances of motion across currents and fields. The skyrmion speed reaches 24 m/s in the plastic flow regime and is surprisingly robust to positional and size variations. Meanwhile, the SkHE saturates at ∼22∘, is substantially reshaped by the wire edge, and crucially increases weakly with skyrmion size. Particle model simulations suggest that the SkHE size dependence — contrary to analytical predictions — arises from the interplay of intrinsic and pinning-driven effects. These results establish a robust framework to harness SkHE and achieve high-throughput skyrmion motion in wire devices. Skyrmions - nanoscale, topological spin textures - are promising elements for next-generation computing due to their efficient coupling to currents in racetrack devices. Here, Tan et al. examine over 20,000 instances of current induced skyrmion motion to unveil a comprehensive picture of skyrmion dynamics across currents and fields.
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Affiliation(s)
- Anthony K C Tan
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore.,Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Pin Ho
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore. .,Institute of Materials Research & Engineering, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore.
| | - James Lourembam
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore.,Institute of Materials Research & Engineering, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore
| | - Lisen Huang
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore.,Institute of Materials Research & Engineering, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore
| | - Hang Khume Tan
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore.,Institute of Materials Research & Engineering, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore
| | - Cynthia J O Reichhardt
- Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Charles Reichhardt
- Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Anjan Soumyanarayanan
- Data Storage Institute, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore. .,Institute of Materials Research & Engineering, Agency for Science, Technology & Research (A*STAR), Singapore, Singapore. .,Physics Department, National University of Singapore, Singapore, Singapore.
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5
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Ghosh A, Ma F, Lourembam J, Jin X, Maddu R, Yap QJ, Ter Lim S. Emergent Dynamics of Artificial Spin-Ice Lattice Based on an Ultrathin Ferromagnet. Nano Lett 2020; 20:109-115. [PMID: 31692358 DOI: 10.1021/acs.nanolett.9b03352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We present high-frequency dynamics of magnetic nanostructure lattices, fabricated in the form of "artificial spin-ice", that possess magnetically frustrated states. Dynamics of such structures feature multiple resonance excitation that reveals rich and intriguing microwave characteristics, which are highly dependent on field-cycle history. Geometrical parameters such as dimensions and ferromagnetic layer thickness, which control the interplay of different demagnetizing factors, are found to play a pivotal role in governing the dynamics. Our findings are highlighted by the evolution of unique excitations pertaining to magnetic frustration, which are well supported by static magnetometry studies and micromagnetic simulations.
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Affiliation(s)
- Abhijit Ghosh
- Data Storage Institute, Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-01 Innovis , Singapore 138634
- Institute of Materials Research and Engineering , Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-03 Innovis , Singapore 138634
| | - Fusheng Ma
- Jangsu Key Laboratory of Optoelectronic Technology, Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology , Nanjing Normal University , Nanjing 210023 , China
| | - James Lourembam
- Data Storage Institute, Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-01 Innovis , Singapore 138634
- Institute of Materials Research and Engineering , Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-03 Innovis , Singapore 138634
| | - Xiangjun Jin
- Jangsu Key Laboratory of Optoelectronic Technology, Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology , Nanjing Normal University , Nanjing 210023 , China
| | - Ramu Maddu
- Data Storage Institute, Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-01 Innovis , Singapore 138634
- Institute of Materials Research and Engineering , Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-03 Innovis , Singapore 138634
| | - Qi Jia Yap
- Data Storage Institute, Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-01 Innovis , Singapore 138634
- Institute of Materials Research and Engineering , Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-03 Innovis , Singapore 138634
| | - Sze Ter Lim
- Data Storage Institute, Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-01 Innovis , Singapore 138634
- Institute of Materials Research and Engineering , Agency for Science Technology and Research (A*STAR) , 2 Fusionopolis Way, #08-03 Innovis , Singapore 138634
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Bera A, Lin W, Yao Y, Ding J, Lourembam J, Wu T. ZnO Nanorods on a LaAlO3 -SrTiO3 Interface: Hybrid 1D-2D Diodes with Engineered Electronic Properties. Small 2016; 12:802-809. [PMID: 26707567 DOI: 10.1002/smll.201502117] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 11/06/2015] [Indexed: 06/05/2023]
Abstract
Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials.
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Affiliation(s)
- Ashok Bera
- Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Weinan Lin
- Division of Physics and Applied Physics, School of Physical and Mathematical science, Nanyang Technological University, Singapore, 637371, Singapore
| | - Yingbang Yao
- Nanofab and Thin Film Core Lab, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Junfeng Ding
- Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - James Lourembam
- Division of Physics and Applied Physics, School of Physical and Mathematical science, Nanyang Technological University, Singapore, 637371, Singapore
| | - Tom Wu
- Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
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7
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Lourembam J, Srivastava A, La-o-vorakiat C, Rotella H, Venkatesan T, Chia EEM. New insights into the diverse electronic phases of a novel vanadium dioxide polymorph: a terahertz spectroscopy study. Sci Rep 2015; 5:9182. [PMID: 25777320 PMCID: PMC4361872 DOI: 10.1038/srep09182] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 02/23/2015] [Indexed: 11/08/2022] Open
Abstract
A remarkable feature of vanadium dioxide is that it can be synthesized in a number of polymorphs. The conductivity mechanism in the metastable layered polymorph VO2(B) thin films has been investigated by terahertz time-domain spectroscopy (THz-TDS). In VO2(B), a critical temperature of 240 K marks the appearance of a non-zero Drude term in the observed complex conductivity, indicating the evolution from a pure insulating state towards a metallic state. In contrast, the THz conductivity of the well-known VO2(M1) is well fitted only by a modification of the Drude model to include backscattering. We also identified two different THz conductivity regimes separated by temperature in these two polymorphs. The electronic phase diagram is constructed, revealing that the width and onset of the metal-insulator transition in the B phase develop differently from the M1 phase.
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Affiliation(s)
- James Lourembam
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Amar Srivastava
- NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Chan La-o-vorakiat
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - H. Rotella
- NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603
| | - T. Venkatesan
- NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore
| | - Elbert E. M. Chia
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
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