1
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Graham AJ, Park H, Nguyen PV, Nunn J, Kandyba V, Cattelan M, Giampietri A, Barinov A, Watanabe K, Taniguchi T, Andreev A, Rudner M, Xu X, Wilson NR, Cobden DH. Conduction Band Replicas in a 2D Moiré Semiconductor Heterobilayer. Nano Lett 2024; 24:5117-5124. [PMID: 38629940 DOI: 10.1021/acs.nanolett.3c04866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
Stacking monolayer semiconductors creates moiré patterns, leading to correlated and topological electronic phenomena, but measurements of the electronic structure underpinning these phenomena are scarce. Here, we investigate the properties of the conduction band in moiré heterobilayers of WS2/WSe2 using submicrometer angle-resolved photoemission spectroscopy with electrostatic gating. We find that at all twist angles the conduction band edge is the K-point valley of the WS2, with a band gap of 1.58 ± 0.03 eV. From the resolved conduction band dispersion, we deduce an effective mass of 0.15 ± 0.02 me. Additionally, we observe replicas of the conduction band displaced by reciprocal lattice vectors of the moiré superlattice. We argue that the replicas result from the moiré potential modifying the conduction band states rather than final-state diffraction. Interestingly, the replicas display an intensity pattern with reduced 3-fold symmetry, which we show implicates the pseudo vector potential associated with in-plane strain in moiré band formation.
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Affiliation(s)
- Abigail J Graham
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
| | - Heonjoon Park
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Paul V Nguyen
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - James Nunn
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
| | - Viktor Kandyba
- Elettra - Sincrotrone Trieste, S.C.p.A, Basovizza (TS), Friuli-Venezia Giulia 34149, Italy
| | - Mattia Cattelan
- Elettra - Sincrotrone Trieste, S.C.p.A, Basovizza (TS), Friuli-Venezia Giulia 34149, Italy
| | - Alessio Giampietri
- Elettra - Sincrotrone Trieste, S.C.p.A, Basovizza (TS), Friuli-Venezia Giulia 34149, Italy
| | - Alexei Barinov
- Elettra - Sincrotrone Trieste, S.C.p.A, Basovizza (TS), Friuli-Venezia Giulia 34149, Italy
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Anton Andreev
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Mark Rudner
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
- Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, United States
| | - Neil R Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
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2
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He M, Cai J, Zhang YH, Liu Y, Li Y, Taniguchi T, Watanabe K, Cobden DH, Yankowitz M, Xu X. Symmetry-Broken Chern Insulators in Twisted Double Bilayer Graphene. Nano Lett 2023. [PMID: 37983529 DOI: 10.1021/acs.nanolett.3c03414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Twisted double bilayer graphene (tDBG) has emerged as a rich platform for studying strongly correlated and topological states, as its flat bands can be continuously tuned by both a perpendicular displacement field and a twist angle. Here, we construct a phase diagram representing the correlated and topological states as a function of these parameters, based on measurements of over a dozen tDBG devices encompassing two distinct stacking configurations. We find a hierarchy of symmetry-broken states that emerge sequentially as the twist angle approaches an apparent optimal value of θ ≈ 1.34°. Nearby this angle, we discover a symmetry-broken Chern insulator (SBCI) state associated with a band filling of 7/2 as well as an incipient SBCI state associated with 11/3 filling. We further observe an anomalous Hall effect at zero field in all samples supporting SBCI states, indicating spontaneous time-reversal symmetry breaking and possible moiré unit cell enlargement at zero magnetic field.
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Affiliation(s)
- Minhao He
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Jiaqi Cai
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Ya-Hui Zhang
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Yang Liu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Yuhao Li
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Matthew Yankowitz
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
- Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, United States
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
- Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, United States
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3
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Wu S, Fei Z, Sun Z, Yi Y, Xia W, Yan D, Guo Y, Shi Y, Yan J, Cobden DH, Liu WT, Xu X, Wu S. Extrinsic Nonlinear Kerr Rotation in Topological Materials under a Magnetic Field. ACS Nano 2023; 17:18905-18913. [PMID: 37767802 DOI: 10.1021/acsnano.3c04153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/29/2023]
Abstract
Topological properties in quantum materials are often governed by symmetry and tuned by crystal structure and external fields, and hence, symmetry-sensitive nonlinear optical measurements in a magnetic field are a valuable probe. Here, we report nonlinear magneto-optical second harmonic generation (SHG) studies of nonmagnetic topological materials including bilayer WTe2, monolayer WSe2, and bulk TaAs. The polarization-resolved patterns of optical SHG under a magnetic field show nonlinear Kerr rotation in these time-reversal symmetric materials. For materials with 3-fold rotational symmetric lattice structure, the SHG polarization pattern rotates just slightly in a magnetic field, whereas in those with mirror or 2-fold rotational symmetry, the SHG polarization pattern rotates greatly and distorts. These different magneto-SHG characters can be understood by considering the superposition of the magnetic field-induced time-noninvariant nonlinear optical tensor and the crystal-structure-based time-invariant counterpart. The situation is further clarified by scrutinizing the Faraday rotation, whose subtle interplay with crystal symmetry accounts for the diverse behavior of the extrinsic nonlinear Kerr rotation in different materials. Our work illustrates the application of magneto-SHG techniques to directly probe nontrivial topological properties, and underlines the importance of minimizing extrinsic nonlinear Kerr rotation in polarization-resolved magneto-optical studies.
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Affiliation(s)
- Shuang Wu
- State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Zeyuan Sun
- State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China
| | - Yangfan Yi
- State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China
| | - Wei Xia
- School of Physical Science and Technology, and ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Dayu Yan
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yanfeng Guo
- School of Physical Science and Technology, and ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Youguo Shi
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Jiaqiang Yan
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Wei-Tao Liu
- State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
- Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, United States
| | - Shiwei Wu
- State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China
- Shanghai Qi Zhi Institute, Shanghai 200232, China
- Institute for Nanoelectronic Devices and Quantum Computing, and Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai 200433, China
- Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
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4
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Zhang S, Liu Y, Sun Z, Chen X, Li B, Moore SL, Liu S, Wang Z, Rossi SE, Jing R, Fonseca J, Yang B, Shao Y, Huang CY, Handa T, Xiong L, Fu M, Pan TC, Halbertal D, Xu X, Zheng W, Schuck PJ, Pasupathy AN, Dean CR, Zhu X, Cobden DH, Xu X, Liu M, Fogler MM, Hone JC, Basov DN. Visualizing moiré ferroelectricity via plasmons and nano-photocurrent in graphene/twisted-WSe 2 structures. Nat Commun 2023; 14:6200. [PMID: 37794007 PMCID: PMC10550968 DOI: 10.1038/s41467-023-41773-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 09/15/2023] [Indexed: 10/06/2023] Open
Abstract
Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) materials. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we employ near-field infrared nano-imaging and nano-photocurrent measurements to study ferroelectricity in minimally twisted WSe2. The ferroelectric domains are visualized through the imaging of the plasmonic response in a graphene monolayer adjacent to the moiré WSe2 bilayers. Specifically, we find that the ferroelectric polarization in moiré domains is imprinted on the plasmonic response of the graphene. Complementary nano-photocurrent measurements demonstrate that the optoelectronic properties of graphene are also modulated by the proximal ferroelectric domains. Our approach represents an alternative strategy for studying moiré ferroelectricity at native length scales and opens promising prospects for (opto)electronic devices.
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Affiliation(s)
- Shuai Zhang
- Department of Physics, Columbia University, New York, NY, 10027, USA.
| | - Yang Liu
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Zhiyuan Sun
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, P.R. China
| | - Xinzhong Chen
- Department of Physics, Columbia University, New York, NY, 10027, USA
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Baichang Li
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - S L Moore
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Song Liu
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Zhiying Wang
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - S E Rossi
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Ran Jing
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Jordan Fonseca
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Birui Yang
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Yinming Shao
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Chun-Ying Huang
- Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - Taketo Handa
- Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - Lin Xiong
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Matthew Fu
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Tsai-Chun Pan
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Dorri Halbertal
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Xinyi Xu
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Wenjun Zheng
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA
| | - P J Schuck
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - A N Pasupathy
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - C R Dean
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Xiaoyang Zhu
- Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Mengkun Liu
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA
| | - M M Fogler
- Department of Physics, University of California, San Diego, La Jolla, CA, 92093, USA
| | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - D N Basov
- Department of Physics, Columbia University, New York, NY, 10027, USA.
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5
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Tseng CC, Song T, Jiang Q, Lin Z, Wang C, Suh J, Watanabe K, Taniguchi T, McGuire MA, Xiao D, Chu JH, Cobden DH, Xu X, Yankowitz M. Gate-Tunable Proximity Effects in Graphene on Layered Magnetic Insulators. Nano Lett 2022; 22:8495-8501. [PMID: 36279401 DOI: 10.1021/acs.nanolett.2c02931] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The extreme versatility of van der Waals materials originates from their ability to exhibit new electronic properties when assembled in close proximity to dissimilar crystals. For example, although graphene is inherently nonmagnetic, recent work has reported a magnetic proximity effect in graphene interfaced with magnetic substrates, potentially enabling a pathway toward achieving a high-temperature quantum anomalous Hall effect. Here, we investigate heterostructures of graphene and chromium trihalide magnetic insulators (CrI3, CrBr3, and CrCl3). Surprisingly, we are unable to detect a magnetic exchange field in the graphene but instead discover proximity effects featuring unprecedented gate tunability. The graphene becomes highly hole-doped due to charge transfer from the neighboring magnetic insulator and further exhibits a variety of atypical gate-dependent transport features. The charge transfer can additionally be altered upon switching the magnetic states of the nearest CrI3 layers. Our results provide a roadmap for exploiting proximity effects arising in graphene coupled to magnetic insulators.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Michael A McGuire
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Di Xiao
- Pacific Northwest National Laboratory, Richland, Washington99354, United States
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6
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Nguyen PV, Teutsch NC, Wilson NP, Kahn J, Xia X, Graham AJ, Kandyba V, Barinov A, Xu X, Cobden DH, Wilson NR. Field-Dependent Band Structure Measurements in Two-Dimensional Heterostructures. Nano Lett 2021; 21:10532-10537. [PMID: 34851122 DOI: 10.1021/acs.nanolett.1c04172] [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: 06/13/2023]
Abstract
In electronic and optoelectronic devices made from van der Waals heterostructures, electric fields can induce substantial band structure changes which are crucial to device operation but cannot usually be directly measured. Here, we use spatially resolved angle-resolved photoemission spectroscopy to monitor changes in band alignment of the component layers, corresponding to band structure changes of the composite heterostructure system, that are produced by electrostatic gating. Our devices comprise graphene on a monolayer semiconductor, WSe2 or MoSe2, atop a boron nitride dielectric and a graphite gate. Applying a gate voltage creates an electric field that shifts the semiconductor bands relative to those in the graphene by up to 0.2 eV. The results can be understood in simple terms by assuming that the materials do not hybridize.
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Affiliation(s)
- Paul V Nguyen
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Natalie C Teutsch
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Nathan P Wilson
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Joshua Kahn
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Xue Xia
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Abigail J Graham
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Viktor Kandyba
- Elettra - Sincrotrone Trieste, S.C.p.A., Basovizza (Trieste) 34149, Italy
| | - Alexei Barinov
- Elettra - Sincrotrone Trieste, S.C.p.A., Basovizza (Trieste) 34149, Italy
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
- Department of Material Science and Engineering, University of Washington, Seattle, Washington 98195, United States
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Neil R Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
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7
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Li Y, Wang X, Tang D, Wang X, Watanabe K, Taniguchi T, Gamelin DR, Cobden DH, Yankowitz M, Xu X, Li J. Unraveling Strain Gradient Induced Electromechanical Coupling in Twisted Double Bilayer Graphene Moiré Superlattices. Adv Mater 2021; 33:e2105879. [PMID: 34632646 DOI: 10.1002/adma.202105879] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 09/14/2021] [Indexed: 06/13/2023]
Abstract
Moiré superlattices of 2D materials with a small twist angle are thought to exhibit appreciable flexoelectric effect, though unambiguous confirmation of their flexoelectricity is challenging due to artifacts associated with commonly used piezoresponse force microscopy (PFM). For example, unexpectedly small phase contrast (≈8°) between opposite flexoelectric polarizations is reported in twisted bilayer graphene (tBG), though theoretically predicted value is 180°. Here a methodology is developed to extract intrinsic moiré flexoelectricity using twisted double bilayer graphene (tDBG) as a model system, probed by lateral PFM. For small twist angle samples, it is found that a vectorial decomposition is essential to recover the small intrinsic flexoelectric response at domain walls from a large background signal. The obtained threefold symmetry of commensurate domains with significant flexoelectric response at domain walls is fully consistent with the theoretical calculations. Incommensurate domains in tDBG with relatively large twist angles can also be observed by this technique. A general strategy is provided here for unraveling intrinsic flexoelectricity in van der Waals moiré superlattices while providing insights into engineered symmetry breaking in centrosymmetric materials.
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Affiliation(s)
- Yuhao Li
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China
| | - Xiao Wang
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China
- Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, 518055, China
| | - Deqi Tang
- Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, 518055, China
| | - Xi Wang
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
- Department of Chemistry, University of Washington, Seattle, WA, 98195, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Daniel R Gamelin
- Department of Chemistry, University of Washington, Seattle, WA, 98195, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Matthew Yankowitz
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, 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
| | - Jiangyu Li
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China
- Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, 518055, China
- Guangdong Provisional Key Laboratory of Functional Oxide Materials and Devices, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China
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8
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Jing R, Shao Y, Fei Z, Lo CFB, Vitalone RA, Ruta FL, Staunton J, Zheng WJC, Mcleod AS, Sun Z, Jiang BY, Chen X, Fogler MM, Millis AJ, Liu M, Cobden DH, Xu X, Basov DN. Terahertz response of monolayer and few-layer WTe 2 at the nanoscale. Nat Commun 2021; 12:5594. [PMID: 34552072 PMCID: PMC8458490 DOI: 10.1038/s41467-021-23933-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 05/17/2021] [Indexed: 02/08/2023] Open
Abstract
Tungsten ditelluride (WTe2) is an atomically layered transition metal dichalcogenide whose physical properties change systematically from monolayer to bilayer and few-layer versions. In this report, we use apertureless scattering-type near-field optical microscopy operating at Terahertz (THz) frequencies and cryogenic temperatures to study the distinct THz range electromagnetic responses of mono-, bi- and trilayer WTe2 in the same multi-terraced micro-crystal. THz nano-images of monolayer terraces uncovered weakly insulating behavior that is consistent with transport measurements. The near-field signal on bilayer regions shows moderate metallicity with negligible temperature dependence. Subdiffractional THz imaging data together with theoretical calculations involving thermally activated carriers favor the semimetal scenario with [Formula: see text] over the semiconductor scenario for bilayer WTe2. Also, we observed clear metallic behavior of the near-field signal on trilayer regions. Our data are consistent with the existence of surface plasmon polaritons in the THz range confined to trilayer terraces in our specimens. Finally, data for microcrystals up to 12 layers thick reveal how the response of a few-layer WTe2 asymptotically approaches the bulk limit.
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Affiliation(s)
- Ran Jing
- Department of Physics, Columbia University, New York, NY, USA.
| | - Yinming Shao
- Department of Physics, Columbia University, New York, NY, USA
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA, USA
| | | | | | - Francesco L Ruta
- Department of Physics, Columbia University, New York, NY, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA
| | - John Staunton
- Department of Physics, Columbia University, New York, NY, USA
| | | | | | - Zhiyuan Sun
- Department of Physics, Columbia University, New York, NY, USA
| | - Bor-Yuan Jiang
- Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Xinzhong Chen
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
| | - Michael M Fogler
- Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Andrew J Millis
- Department of Physics, Columbia University, New York, NY, USA
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA
| | - Mengkun Liu
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA
- Department of Material Science and Engineering, University of Washington, Seattle, WA, USA
| | - D N Basov
- Department of Physics, Columbia University, New York, NY, USA
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9
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Zhao W, Fei Z, Song T, Choi HK, Palomaki T, Sun B, Malinowski P, McGuire MA, Chu JH, Xu X, Cobden DH. Magnetic proximity and nonreciprocal current switching in a monolayer WTe 2 helical edge. Nat Mater 2020; 19:503-507. [PMID: 32152559 DOI: 10.1038/s41563-020-0620-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 01/21/2020] [Indexed: 06/10/2023]
Abstract
The integration of diverse electronic phenomena, such as magnetism and nontrivial topology, into a single system is normally studied either by seeking materials that contain both ingredients, or by layered growth of contrasting materials1-9. The ability to simply stack very different two-dimensional van der Waals materials in intimate contact permits a different approach10,11. Here we use this approach to couple the helical edges states in a two-dimensional topological insulator, monolayer WTe2 (refs. 12-16), to a two-dimensional layered antiferromagnet, CrI3 (ref. 17). We find that the edge conductance is sensitive to the magnetization state of the CrI3, and the coupling can be understood in terms of an exchange field from the nearest and next-nearest CrI3 layers that produces a gap in the helical edge. We also find that the nonlinear edge conductance depends on the magnetization of the nearest CrI3 layer relative to the current direction. At low temperatures this produces an extraordinarily large nonreciprocal current that is switched by changing the antiferromagnetic state of the CrI3.
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Affiliation(s)
- Wenjin Zhao
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Tiancheng Song
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Han Kyou Choi
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Tauno Palomaki
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Bosong Sun
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Paul Malinowski
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Michael A McGuire
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Jiun-Haw Chu
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, USA.
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10
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Song T, Fei Z, Yankowitz M, Lin Z, Jiang Q, Hwangbo K, Zhang Q, Sun B, Taniguchi T, Watanabe K, McGuire MA, Graf D, Cao T, Chu JH, Cobden DH, Dean CR, Xiao D, Xu X. Switching 2D magnetic states via pressure tuning of layer stacking. Nat Mater 2019; 18:1298-1302. [PMID: 31659293 DOI: 10.1038/s41563-019-0505-2] [Citation(s) in RCA: 153] [Impact Index Per Article: 30.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Accepted: 09/11/2019] [Indexed: 06/10/2023]
Abstract
The physical properties of two-dimensional van der Waals crystals can be sensitive to interlayer coupling. For two-dimensional magnets1-3, theory suggests that interlayer exchange coupling is strongly dependent on layer separation while the stacking arrangement can even change the sign of the interlayer magnetic exchange, thus drastically modifying the ground state4-10. Here, we demonstrate pressure tuning of magnetic order in the two-dimensional magnet CrI3. We probe the magnetic states using tunnelling8,11-13 and scanning magnetic circular dichroism microscopy measurements2. We find that interlayer magnetic coupling can be more than doubled by hydrostatic pressure. In bilayer CrI3, pressure induces a transition from layered antiferromagnetic to ferromagnetic phase. In trilayer CrI3, pressure can create coexisting domains of three phases, one ferromagnetic and two antiferromagnetic. The observed changes in magnetic order can be explained by changes in the stacking arrangement. Such coupling between stacking order and magnetism provides ample opportunities for designer magnetic phases and functionalities.
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Affiliation(s)
- Tiancheng Song
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA, USA
| | | | - Zhong Lin
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Qianni Jiang
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Kyle Hwangbo
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Qi Zhang
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Bosong Sun
- Department of Physics, University of Washington, Seattle, WA, USA
| | | | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | - Michael A McGuire
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - David Graf
- National High Magnetic Field Laboratory, Tallahassee, FL, USA
| | - Ting Cao
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA
| | - Jiun-Haw Chu
- Department of Physics, University of Washington, Seattle, WA, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Cory R Dean
- Department of Physics, Columbia University, New York, NY, USA
| | - Di Xiao
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
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11
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Nguyen PV, Teutsch NC, Wilson NP, Kahn J, Xia X, Graham AJ, Kandyba V, Giampietri A, Barinov A, Constantinescu GC, Yeung N, Hine NDM, Xu X, Cobden DH, Wilson NR. Visualizing electrostatic gating effects in two-dimensional heterostructures. Nature 2019; 572:220-223. [DOI: 10.1038/s41586-019-1402-1] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 05/07/2019] [Indexed: 11/09/2022]
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12
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Cai X, Song T, Wilson NP, Clark G, He M, Zhang X, Taniguchi T, Watanabe K, Yao W, Xiao D, McGuire MA, Cobden DH, Xu X. Atomically Thin CrCl 3: An In-Plane Layered Antiferromagnetic Insulator. Nano Lett 2019; 19:3993-3998. [PMID: 31083954 DOI: 10.1021/acs.nanolett.9b01317] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The recent discovery of magnetism in atomically thin layers of van der Waals (vdW) crystals has created new opportunities for exploring magnetic phenomena in the two-dimensional (2D) limit. In most 2D magnets studied to date, the c-axis is an easy axis, so that at zero applied field the polarization of each layer is perpendicular to the plane. Here, we demonstrate that atomically thin CrCl3 is a layered antiferromagnetic insulator with an easy-plane normal to the c-axis, that is, the polarization is in the plane of each layer and has no preferred direction within it. Ligand-field photoluminescence at 870 nm is observed down to the monolayer limit, demonstrating its insulating properties. We investigate the in-plane magnetic order using tunneling magnetoresistance in graphene/CrCl3/graphene tunnel junctions, establishing that the interlayer coupling is antiferromagnetic down to the bilayer. From the temperature dependence of the magnetoresistance, we obtain an effective magnetic phase diagram for the bilayer. Our result shows that CrCl3 should be useful for studying the physics of 2D phase transitions and for making new kinds of vdW spintronic devices.
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Affiliation(s)
- Xinghan Cai
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
- National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Department of Micro/Nano Electronics , Shanghai Jiao Tong University , Shanghai 200240 , China
| | - Tiancheng Song
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Nathan P Wilson
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Genevieve Clark
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195 , United States
| | - Minhao He
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Xiaoou Zhang
- Department of Physics , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Takashi Taniguchi
- National Institute for Materials Science , Tsukuba , Ibaraki 305-0044 , Japan
| | - Kenji Watanabe
- National Institute for Materials Science , Tsukuba , Ibaraki 305-0044 , Japan
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics , University of Hong Kong , Hong Kong , China
| | - Di Xiao
- Department of Physics , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Michael A McGuire
- Materials Science and Technology Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - David H Cobden
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Xiaodong Xu
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195 , United States
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13
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Song T, Tu MWY, Carnahan C, Cai X, Taniguchi T, Watanabe K, McGuire MA, Cobden DH, Xiao D, Yao W, Xu X. Voltage Control of a van der Waals Spin-Filter Magnetic Tunnel Junction. Nano Lett 2019; 19:915-920. [PMID: 30620202 DOI: 10.1021/acs.nanolett.8b04160] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Atomically thin chromium triiodide (CrI3) has recently been identified as a layered antiferromagnetic insulator, in which adjacent ferromagnetic monolayers are antiferromagnetically coupled. This unusual magnetic structure naturally comprises a series of antialigned spin filters, which can be utilized to make spin-filter magnetic tunnel junctions with very large tunneling magnetoresistance (TMR). Here we report voltage control of TMR formed by four-layer CrI3 sandwiched by monolayer graphene contacts in a dual-gated structure. By varying the gate voltages at fixed magnetic field, the device can be switched reversibly between bistable magnetic states with the same net magnetization but drastically different resistance (by a factor of 10 or more). In addition, without switching the state, the TMR can be continuously modulated between 17,000% and 57,000%, due to the combination of spin-dependent tunnel barrier with changing carrier distributions in the graphene contacts. Our work demonstrates new kinds of magnetically moderated transistor action and opens up possibilities for voltage-controlled van der Waals spintronic devices.
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Affiliation(s)
- Tiancheng Song
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Matisse Wei-Yuan Tu
- Department of Physics and Center of Theoretical and Computational Physics , University of Hong Kong , Hong Kong , China
| | - Caitlin Carnahan
- Department of Physics , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Xinghan Cai
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Takashi Taniguchi
- National Institute for Materials Science , Tsukuba , Ibaraki 305-0044 , Japan
| | - Kenji Watanabe
- National Institute for Materials Science , Tsukuba , Ibaraki 305-0044 , Japan
| | - Michael A McGuire
- Materials Science and Technology Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - David H Cobden
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
| | - Di Xiao
- Department of Physics , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics , University of Hong Kong , Hong Kong , China
| | - Xiaodong Xu
- Department of Physics , University of Washington , Seattle , Washington 98195 , United States
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195 , United States
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14
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Shi Y, Kahn J, Niu B, Fei Z, Sun B, Cai X, Francisco BA, Wu D, Shen ZX, Xu X, Cobden DH, Cui YT. Imaging quantum spin Hall edges in monolayer WTe 2. Sci Adv 2019; 5:eaat8799. [PMID: 30783621 PMCID: PMC6368433 DOI: 10.1126/sciadv.aat8799] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 12/21/2018] [Indexed: 05/13/2023]
Abstract
A two-dimensional (2D) topological insulator exhibits the quantum spin Hall (QSH) effect, in which topologically protected conducting channels exist at the sample edges. Experimental signatures of the QSH effect have recently been reported in an atomically thin material, monolayer WTe2. Here, we directly image the local conductivity of monolayer WTe2 using microwave impedance microscopy, establishing beyond doubt that conduction is indeed strongly localized to the physical edges at temperatures up to 77 K and above. The edge conductivity shows no gap as a function of gate voltage, and is suppressed by magnetic field as expected. We observe additional conducting features which can be explained by edge states following boundaries between topologically trivial and nontrivial regions. These observations will be critical for interpreting and improving the properties of devices incorporating WTe2. Meanwhile, they reveal the robustness of the QSH channels and the potential to engineer them in the monolayer material platform.
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Affiliation(s)
- Yanmeng Shi
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
| | - Joshua Kahn
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Ben Niu
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Bosong Sun
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Xinghan Cai
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Brian A. Francisco
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
| | - Di Wu
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Zhi-Xun Shen
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA 98195, USA
- Corresponding author. (X.X.); (D.H.C.); (Y.-T.C.)
| | - David H. Cobden
- Department of Physics, University of Washington, Seattle, WA 98195, USA
- Corresponding author. (X.X.); (D.H.C.); (Y.-T.C.)
| | - Yong-Tao Cui
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Corresponding author. (X.X.); (D.H.C.); (Y.-T.C.)
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15
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Sajadi E, Palomaki T, Fei Z, Zhao W, Bement P, Olsen C, Luescher S, Xu X, Folk JA, Cobden DH. Gate-induced superconductivity in a monolayer topological insulator. Science 2018; 362:922-925. [PMID: 30361385 DOI: 10.1126/science.aar4426] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2017] [Accepted: 10/05/2018] [Indexed: 01/14/2023]
Abstract
The layered semimetal tungsten ditelluride (WTe2) has recently been found to be a two-dimensional topological insulator (2D TI) when thinned down to a single monolayer, with conducting helical edge channels. We found that intrinsic superconductivity can be induced in this monolayer 2D TI by mild electrostatic doping at temperatures below 1 kelvin. The 2D TI-superconductor transition can be driven by applying a small gate voltage. This discovery offers possibilities for gate-controlled devices combining superconductivity and nontrivial topological properties, and could provide a basis for quantum information schemes based on topological protection.
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Affiliation(s)
- Ebrahim Sajadi
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada, and Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Tauno Palomaki
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Wenjin Zhao
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Philip Bement
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada, and Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Christian Olsen
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada, and Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Silvia Luescher
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada, and Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - 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
| | - Joshua A Folk
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada, and Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA 98195, USA.
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16
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Fei Z, Huang B, Malinowski P, Wang W, Song T, Sanchez J, Yao W, Xiao D, Zhu X, May AF, Wu W, Cobden DH, Chu JH, Xu X. Two-dimensional itinerant ferromagnetism in atomically thin Fe 3GeTe 2. Nat Mater 2018; 17:778-782. [PMID: 30104669 DOI: 10.1038/s41563-018-0149-7] [Citation(s) in RCA: 390] [Impact Index Per Article: 65.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 07/13/2018] [Indexed: 05/20/2023]
Abstract
Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins1-4. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that Fe3GeTe2 (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (TC) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces an atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant ferromagnetism and for engineering spintronic vdW heterostructures5.
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Affiliation(s)
- Zaiyao Fei
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Bevin Huang
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Paul Malinowski
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Wenbo Wang
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, USA
| | - Tiancheng Song
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Joshua Sanchez
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Di Xiao
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Xiaoyang Zhu
- Department of Chemistry, Columbia University, New York, NY, USA
| | - Andrew F May
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Weida Wu
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Jiun-Haw Chu
- Department of Physics, University of Washington, Seattle, WA, USA.
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
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17
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Fei Z, Zhao W, Palomaki TA, Sun B, Miller MK, Zhao Z, Yan J, Xu X, Cobden DH. Ferroelectric switching of a two-dimensional metal. Nature 2018; 560:336-339. [DOI: 10.1038/s41586-018-0336-3] [Citation(s) in RCA: 339] [Impact Index Per Article: 56.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 05/25/2018] [Indexed: 11/09/2022]
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18
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Huang B, Clark G, Klein DR, MacNeill D, Navarro-Moratalla E, Seyler KL, Wilson N, McGuire MA, Cobden DH, Xiao D, Yao W, Jarillo-Herrero P, Xu X. Electrical control of 2D magnetism in bilayer CrI 3. Nat Nanotechnol 2018; 13:544-548. [PMID: 29686292 DOI: 10.1038/s41565-018-0121-3] [Citation(s) in RCA: 352] [Impact Index Per Article: 58.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 03/21/2018] [Indexed: 05/26/2023]
Abstract
Controlling magnetism via electric fields addresses fundamental questions of magnetic phenomena and phase transitions1-3, and enables the development of electrically coupled spintronic devices, such as voltage-controlled magnetic memories with low operation energy4-6. Previous studies on dilute magnetic semiconductors such as (Ga,Mn)As and (In,Mn)Sb have demonstrated large modulations of the Curie temperatures and coercive fields by altering the magnetic anisotropy and exchange interaction2,4,7-9. Owing to their unique magnetic properties10-14, the recently reported two-dimensional magnets provide a new system for studying these features15-19. For instance, a bilayer of chromium triiodide (CrI3) behaves as a layered antiferromagnet with a magnetic field-driven metamagnetic transition15,16. Here, we demonstrate electrostatic gate control of magnetism in CrI3 bilayers, probed by magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage-controlled switching between antiferromagnetic and ferromagnetic states. At zero magnetic field, we demonstrate a time-reversal pair of layered antiferromagnetic states that exhibit spin-layer locking, leading to a linear dependence of their MOKE signals on gate voltage with opposite slopes. Our results allow for the exploration of new magnetoelectric phenomena and van der Waals spintronics based on 2D materials.
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Affiliation(s)
- Bevin Huang
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Genevieve Clark
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA
| | - Dahlia R Klein
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - David MacNeill
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Kyle L Seyler
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Nathan Wilson
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Michael A McGuire
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Di Xiao
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | | | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
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19
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Song T, Cai X, Tu MWY, Zhang X, Huang B, Wilson NP, Seyler KL, Zhu L, Taniguchi T, Watanabe K, McGuire MA, Cobden DH, Xiao D, Yao W, Xu X. Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures. Science 2018; 360:1214-1218. [DOI: 10.1126/science.aar4851] [Citation(s) in RCA: 648] [Impact Index Per Article: 108.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 04/24/2018] [Indexed: 01/19/2023]
Abstract
Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance that is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.
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20
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Wilson NR, Nguyen PV, Seyler K, Rivera P, Marsden AJ, Laker ZP, Constantinescu GC, Kandyba V, Barinov A, Hine ND, Xu X, Cobden DH. Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures. Sci Adv 2017; 3:e1601832. [PMID: 28246636 PMCID: PMC5298850 DOI: 10.1126/sciadv.1601832] [Citation(s) in RCA: 127] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 12/19/2016] [Indexed: 05/21/2023]
Abstract
Combining monolayers of different two-dimensional semiconductors into heterostructures creates new phenomena and device possibilities. Understanding and exploiting these phenomena hinge on knowing the electronic structure and the properties of interlayer excitations. We determine the key unknown parameters in MoSe2/WSe2 heterobilayers by using rational device design and submicrometer angle-resolved photoemission spectroscopy (μ-ARPES) in combination with photoluminescence. We find that the bands in the K-point valleys are weakly hybridized, with a valence band offset of 300 meV, implying type II band alignment. We deduce that the binding energy of interlayer excitons is more than 200 meV, an order of magnitude higher than that in analogous GaAs structures. Hybridization strongly modifies the bands at Γ, but the valence band edge remains at the K points. We also find that the spectrum of a rotationally aligned heterobilayer reflects a mixture of commensurate and incommensurate domains. These results directly answer many outstanding questions about the electronic nature of MoSe2/WSe2 heterobilayers and demonstrate a practical approach for high spectral resolution in ARPES of device-scale structures.
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Affiliation(s)
- Neil R. Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K
- Corresponding author. (D.H.C.); (N.R.W.); (X.X.)
| | - Paul V. Nguyen
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Kyle Seyler
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Pasqual Rivera
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | | | | | - Gabriel C. Constantinescu
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, U.K
| | - Viktor Kandyba
- Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, 34149 Trieste, Italy
- Physics Department, University of Trieste, Via Valerio 2, 34127 Trieste, Italy
| | - Alexei Barinov
- Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, 34149 Trieste, Italy
| | | | - 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
- Corresponding author. (D.H.C.); (N.R.W.); (X.X.)
| | - David H. Cobden
- Department of Physics, University of Washington, Seattle, WA 98195, USA
- Corresponding author. (D.H.C.); (N.R.W.); (X.X.)
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21
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Kasırga TS, Coy JM, Park JH, Cobden DH. Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2. Nanotechnology 2016; 27:345708. [PMID: 27454751 DOI: 10.1088/0957-4484/27/34/345708] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 °C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient, [Formula: see text] applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques.
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Affiliation(s)
- T Serkan Kasırga
- Department of Physics, University of Washington, Seattle, WA 98195, USA. UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, Turkey
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Huang C, Wu S, Sanchez AM, Peters JJP, Beanland R, Ross JS, Rivera P, Yao W, Cobden DH, Xu X. Lateral heterojunctions within monolayer MoSe2-WSe2 semiconductors. Nat Mater 2014; 13:1096-101. [PMID: 25150560 DOI: 10.1038/nmat4064] [Citation(s) in RCA: 405] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Accepted: 07/23/2014] [Indexed: 05/02/2023]
Abstract
Heterojunctions between three-dimensional (3D) semiconductors with different bandgaps are the basis of modern light-emitting diodes, diode lasers and high-speed transistors. Creating analogous heterojunctions between different 2D semiconductors would enable band engineering within the 2D plane and open up new realms in materials science, device physics and engineering. Here we demonstrate that seamless high-quality in-plane heterojunctions can be grown between the 2D monolayer semiconductors MoSe2 and WSe2. The junctions, grown by lateral heteroepitaxy using physical vapour transport, are visible in an optical microscope and show enhanced photoluminescence. Atomically resolved transmission electron microscopy reveals that their structure is an undistorted honeycomb lattice in which substitution of one transition metal by another occurs across the interface. The growth of such lateral junctions will allow new device functionalities, such as in-plane transistors and diodes, to be integrated within a single atomically thin layer.
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Affiliation(s)
- Chunming Huang
- 1] Department of Physics, University of Washington, Seattle, Washington 98195, USA [2]
| | - Sanfeng Wu
- 1] Department of Physics, University of Washington, Seattle, Washington 98195, USA [2]
| | - Ana M Sanchez
- 1] Department of Physics, University of Warwick, Coventry, CV4 7AL, UK [2]
| | | | - Richard Beanland
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - Jason S Ross
- Department of Material Science and Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Pasqual Rivera
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - Xiaodong Xu
- 1] Department of Physics, University of Washington, Seattle, Washington 98195, USA [2] Department of Material Science and Engineering, University of Washington, Seattle, Washington 98195, USA
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Ross JS, Klement P, Jones AM, Ghimire NJ, Yan J, Mandrus DG, Taniguchi T, Watanabe K, Kitamura K, Yao W, Cobden DH, Xu X. Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p-n junctions. Nat Nanotechnol 2014; 9:268-72. [PMID: 24608230 DOI: 10.1038/nnano.2014.26] [Citation(s) in RCA: 662] [Impact Index Per Article: 66.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Accepted: 01/21/2014] [Indexed: 05/22/2023]
Abstract
The development of light-emitting diodes with improved efficiency, spectral properties, compactness and integrability is important for lighting, display, optical interconnect, logic and sensor applications. Monolayer transition-metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties. Electroluminescence has already been observed from monolayer MoS2 devices. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of the MoS2 and to ineffective contacts. Here, we report electroluminescence from lateral p-n junctions in monolayer WSe2 induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe2, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than in MoS2 (refs 17,18). Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. This system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.
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Affiliation(s)
- Jason S Ross
- Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Philip Klement
- 1] Department of Physics, Justus Liebig University, 35392 Giessen, Germany [2] Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - Aaron M Jones
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - Nirmal J Ghimire
- 1] Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831, USA
| | - Jiaqiang Yan
- 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831, USA [2] Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - D G Mandrus
- 1] Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831, USA [3] Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Kitamura
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - David H Cobden
- Department of Physics, Justus Liebig University, 35392 Giessen, Germany
| | - Xiaodong Xu
- 1] Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA [2] Department of Physics, Justus Liebig University, 35392 Giessen, Germany
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Park JH, Coy JM, Kasirga TS, Huang C, Fei Z, Hunter S, Cobden DH. Measurement of a solid-state triple point at the metal-insulator transition in VO2. Nature 2013; 500:431-4. [PMID: 23969461 DOI: 10.1038/nature12425] [Citation(s) in RCA: 335] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 06/24/2013] [Indexed: 11/09/2022]
Abstract
First-order phase transitions in solids are notoriously challenging to study. The combination of change in unit cell shape, long range of elastic distortion and flow of latent heat leads to large energy barriers resulting in domain structure, hysteresis and cracking. The situation is worse near a triple point, where more than two phases are involved. The well-known metal-insulator transition in vanadium dioxide, a popular candidate for ultrafast optical and electrical switching applications, is a case in point. Even though VO2 is one of the simplest strongly correlated materials, experimental difficulties posed by the first-order nature of the metal-insulator transition as well as the involvement of at least two competing insulating phases have led to persistent controversy about its nature. Here we show that studying single-crystal VO2 nanobeams in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision. Our results include the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature, Ttr = Tc, which we determine to be 65.0 ± 0.1 °C. The findings have profound implications for the mechanism of the metal-insulator transition in VO2, but they also demonstrate the importance of this approach for mastering phase transitions in many other strongly correlated materials, such as manganites and iron-based superconductors.
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Affiliation(s)
- Jae Hyung Park
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
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Wu S, Huang C, Aivazian G, Ross JS, Cobden DH, Xu X. Vapor-solid growth of high optical quality MoS₂ monolayers with near-unity valley polarization. ACS Nano 2013; 7:2768-72. [PMID: 23427810 DOI: 10.1021/nn4002038] [Citation(s) in RCA: 174] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Monolayers of transition metal dichalcogenides (TMDCs) are atomically thin direct-gap semiconductors with potential applications in nanoelectronics, optoelectronics, and electrochemical sensing. Recent theoretical and experimental efforts suggest that they are ideal systems for exploiting the valley degrees of freedom of Bloch electrons. For example, Dirac valley polarization has been demonstrated in mechanically exfoliated monolayer MoS2 samples by polarization-resolved photoluminescence, although polarization has rarely been seen at room temperature. Here we report a new method for synthesizing high optical quality monolayer MoS2 single crystals up to 25 μm in size on a variety of standard insulating substrates (SiO2, sapphire, and glass) using a catalyst-free vapor-solid growth mechanism. The technique is simple and reliable, and the optical quality of the crystals is extremely high, as demonstrated by the fact that the valley polarization approaches unity at 30 K and persists at 35% even at room temperature, suggesting a virtual absence of defects. This will allow greatly improved optoelectronic TMDC monolayer devices to be fabricated and studied routinely.
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Affiliation(s)
- Sanfeng Wu
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
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26
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Kasırga TS, Sun D, Park JH, Coy JM, Fei Z, Xu X, Cobden DH. Photoresponse of a strongly correlated material determined by scanning photocurrent microscopy. Nat Nanotechnol 2012; 7:723-7. [PMID: 23085645 DOI: 10.1038/nnano.2012.176] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Accepted: 09/13/2012] [Indexed: 05/08/2023]
Abstract
The generation of a current by light is a key process in optoelectronic and photovoltaic devices. In band semiconductors, depletion fields associated with interfaces separate long-lived photo-induced carriers. However, in systems with strong electron-electron and electron-phonon correlations it is unclear what physics will dominate the photoresponse. Here, we investigate photocurrent in VO(2), an exemplary strongly correlated material known for its dramatic metal-insulator transition at T(c) ≈ 68 °C, which could be useful for optoelectronic detection and switching up to ultraviolet wavelengths. Using scanning photocurrent microscopy on individual suspended VO(2) nanobeams we observe a photoresponse peaked at the metal-insulator boundary but extending throughout both insulating and metallic phases. We determine that the response is photothermal, implying efficient carrier relaxation to a local equilibrium in a manner consistent with strong correlations. Temperature-dependent measurements reveal subtle phase changes within the insulating state. We further demonstrate switching of the photocurrent by optical control of the metal-insulator boundary arrangement. Our work shows the value of applying scanning photocurrent microscopy to nanoscale crystals in the investigation of strongly correlated materials, and the results are relevant for designing and controlling optoelectronic devices employing such materials.
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Affiliation(s)
- T Serkan Kasırga
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
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Affiliation(s)
- Zenghui Wang
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
| | - Jiang Wei
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
| | - Peter Morse
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
| | - J. Gregory Dash
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
| | - Oscar E. Vilches
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
| | - David H. Cobden
- Department of Physics, University of Washington, Seattle, WA 98195–1560, USA
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Wei J, Wang Z, Chen W, Cobden DH. New aspects of the metal-insulator transition in single-domain vanadium dioxide nanobeams. Nat Nanotechnol 2009; 4:420-424. [PMID: 19581893 DOI: 10.1038/nnano.2009.141] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Accepted: 05/05/2009] [Indexed: 05/28/2023]
Abstract
Many strongly correlated electronic materials have a domain structure that greatly influences the bulk properties and obscures the fundamental properties of the homogeneous material. Nanoscale samples, on the other hand, can be smaller than the characteristic domain size, thus making it possible to explore these fundamental properties in detail. Here, we report new aspects of the metal-insulator transition, studied in single-domain vanadium dioxide nanobeams. We have observed supercooling of the metallic phase by 50 degrees C, an activation energy in the insulating phase that is consistent with the optical gap, and a connection between the metal-insulator transition and the equilibrium carrier density in the insulating phase. Our devices also provide a nanomechanical method for determining the transition temperature, enable measurements on individual metal-insulator interphase walls to be made, and allow general investigations of phase transitions in quasi-one-dimensional geometries.
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Affiliation(s)
- Jiang Wei
- Department of Physics, University of Washington, Seattle, Washington, USA
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29
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Buitelaar MR, Kashcheyevs V, Leek PJ, Talyanskii VI, Smith CG, Anderson D, Jones GAC, Wei J, Cobden DH. Adiabatic charge pumping in carbon nanotube quantum dots. Phys Rev Lett 2008; 101:126803. [PMID: 18851400 DOI: 10.1103/physrevlett.101.126803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Indexed: 05/26/2023]
Abstract
We investigate charge pumping in carbon nanotube quantum dots driven by the electric field of a surface acoustic wave. We find that, at small driving amplitudes, the pumped current reverses polarity as the conductance is tuned through a Coulomb blockade peak using a gate electrode. We study the behavior as a function of wave amplitude, frequency, and direction and develop a model in which our results can be understood as resulting from adiabatic charge redistribution between the leads and quantum dots on the nanotube.
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Affiliation(s)
- M R Buitelaar
- Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
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Abstract
We introduce a technique that improves the sensitivity and resolution and eliminates the nonlocal background of scanned gate microscopy (SGM). In conventional SGM, a voltage bias is applied to the atomic force microscope tip and the sample conductance is measured as the tip is scanned. In the new technique, which we call tip-modulation SGM (tmSGM), the biased tip is oscillated and the induced oscillation of the sample conductance is measured. Applied to single-walled carbon nanotube network devices, tmSGM gives sharp, low-noise and background-free images.
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Affiliation(s)
- Neil R Wilson
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK.
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Abstract
By slowing the rate of atomic addition to singly twinned seeds, we have grown silver nanobeams with lengths of 3-30 mum, widths ranging from 17 to 70 nm, and a width to thickness ratio of 1.4. The well-defined dimensions, smooth surface, and crystallinity of nanobeams make them promising candidates for studying the effects of size on electron transport. With a simple method that allows rapid characterization of single nanobeams, we find that even the thinnest nanobeams largely retain the low resistivity of bulk silver. Nanobeams can support remarkably high current densities of up to 2.6 x 10(8) A cm(-2) before the conduction path is broken by the formation of a nanogap.
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Affiliation(s)
- Benjamin J Wiley
- Departments of Chemical Engineering, Physics, and Chemistry, University of Washington, Seattle, Washington 98195, USA
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Leek PJ, Buitelaar MR, Talyanskii VI, Smith CG, Anderson D, Jones GAC, Wei J, Cobden DH. Charge pumping in carbon nanotubes. Phys Rev Lett 2005; 95:256802. [PMID: 16384490 DOI: 10.1103/physrevlett.95.256802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Indexed: 05/05/2023]
Abstract
We demonstrate charge pumping in semiconducting carbon nanotubes by a traveling potential wave. From the observation of pumping in the nanotube insulating state we deduce that transport occurs by packets of charge being carried along by the wave. By tuning the potential of a side gate, transport of either electron or hole packets can be realized. Prospects for the realization of nanotube based single-electron pumps are discussed.
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Affiliation(s)
- P J Leek
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, United Kingdom
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Spivak B, Zyuzin A, Cobden DH. Mesoscopic oscillations of the conductance of disordered metallic samples as a function of temperature. Phys Rev Lett 2005; 95:226804. [PMID: 16384253 DOI: 10.1103/physrevlett.95.226804] [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] [Received: 04/19/2005] [Indexed: 05/05/2023]
Abstract
We show theoretically and experimentally that the conductance of small disordered samples exhibits random oscillations as a function of temperature. The amplitude of the oscillations decays as a power law of temperature, and their characteristic period is of the order of the temperature itself.
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Affiliation(s)
- B Spivak
- Physics Department, University of Washington, Seattle, Washington 98195, USA
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Affiliation(s)
- Neil R. Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K., Department of Physics, University of Washington, Seattle, Washington 98198-31560, and Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
| | - David H. Cobden
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K., Department of Physics, University of Washington, Seattle, Washington 98198-31560, and Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
| | - Julie V. Macpherson
- Department of Physics, University of Warwick, Coventry CV4 7AL, U.K., Department of Physics, University of Washington, Seattle, Washington 98198-31560, and Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K
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Abstract
We observe twofold shell filling in the spectra of closed one-dimensional quantum dots formed in single-wall carbon nanotubes. Its signatures include a bimodal distribution of addition energies, correlations in the excitation spectra for different electron number, and alternation of the spins of the added electrons. This provides a contrast with quantum dots in higher dimensions, where such spin pairing is absent. We also see indications of an additional fourfold periodicity indicative of K-K' subband shells. Our results suggest that the absence of shell filling in most isolated nanotube dots results from disorder or nonuniformity.
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Affiliation(s)
- David H Cobden
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA.
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Abstract
The connection of electrical leads to wire-like molecules is a logical step in the development of molecular electronics, but also allows studies of fundamental physics. For example, metallic carbon nanotubes are quantum wires that have been found to act as one-dimensional quantum dots, Luttinger liquids, proximity-induced superconductors and ballistic and diffusive one-dimensional metals. Here we report that electrically contacted single-walled carbon nanotubes can serve as powerful probes of Kondo physics, demonstrating the universality of the Kondo effect. Arising in the prototypical case from the interaction between a localized impurity magnetic moment and delocalized electrons in a metallic host, the Kondo effect has been used to explain enhanced low-temperature scattering from magnetic impurities in metals, and also occurs in transport through semiconductor quantum dots. The far greater tunability of dots (in our case, nanotubes) compared with atomic impurities renders new classes of Kondo-like effects accessible. Our nanotube devices differ from previous systems in which Kondo effects have been observed, in that they are one-dimensional quantum dots with three-dimensional metal (gold) reservoirs. This allows us to observe Kondo resonances for very large electron numbers (N) in the dot, and approaching the unitary limit (where the transmission reaches its maximum possible value). Moreover, we detect a previously unobserved Kondo effect, occurring for even values of N in a magnetic field.
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Affiliation(s)
- J Nygård
- Orsted Laboratory, Niels Bohr Institute, Copenhagen, Denmark
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Cobden DH. A nanotube laboratory. Nature 1999. [DOI: 10.1038/17682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
The electrical properties of individual bundles, or "ropes," of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.
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Affiliation(s)
- M Bockrath
- M. Bockrath, D. H. Cobden, P. L. McEuen, N. G. Chopra, A. Zettl, Molecular Design Institute, Lawrence Berkeley National Laboratory, and Department of Physics, University of California, Berkeley, CA 94720, USA. A. Thess and R. E. Smalley, Center for Nanoscale Science and Technology, Rice Quantum Institute, and Departments of Chemistry and Physics, Mail Stop 100, Rice University, Post Office Box 1892, Houston, TX 77251, USA
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Cobden DH, Kogan E. Measurement of the conductance distribution function at a quantum Hall transition. Phys Rev B Condens Matter 1996; 54:R17316-R17319. [PMID: 9985946 DOI: 10.1103/physrevb.54.r17316] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Cobden DH, Muzykantskii BA. Finite-Temperature Fermi-Edge Singularity in Tunneling Studied Using Random Telegraph Signals. Phys Rev Lett 1995; 75:4274-4277. [PMID: 10059863 DOI: 10.1103/physrevlett.75.4274] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Morgan A, Cobden DH, Pepper M, Jin G, Tang YS, Wilkinson CD. Resistance fluctuations in diffusive transport at high magnetic fields in narrrow Si transistors. Phys Rev B Condens Matter 1994; 50:12187-12190. [PMID: 9975366 DOI: 10.1103/physrevb.50.12187] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Cobden DH, Savchenko A, Pepper M, Patel NK, Ritchie DA, Frost JE, Jones GA. Time-irreversible random telegraph signal due to current along a single hopping chain. Phys Rev Lett 1992; 69:502-505. [PMID: 10046955 DOI: 10.1103/physrevlett.69.502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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45
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Cobden DH, Patel NK, Pepper M, Ritchie DA, Frost JE, Jones GA. Noise and reproducible structure in a GaAs/AlxGa1-xAs one-dimensional channel. Phys Rev B Condens Matter 1991; 44:1938-1941. [PMID: 9999738 DOI: 10.1103/physrevb.44.1938] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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