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Wang S, Tian H, Sun M. Valley-polarized and enhanced transmission in graphene with a smooth strain profile. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:304002. [PMID: 37040781 DOI: 10.1088/1361-648x/accbf9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Accepted: 04/11/2023] [Indexed: 06/19/2023]
Abstract
We explore the influence of strain on the valley-polarized transmission of graphene by employing the wave-function matching and the non-equilibrium Green's function technique. When the transmission is along the armchair direction, we show that the valley polarization and transmission can be improved by increasing the width of the strained region and increasing (decreasing) the extensional strain in the armchair (zigzag) direction. It is noted that the shear strain does not affect transmission and valley polarization. Furthermore, when we consider the smooth strain barrier, the valley-polarized transmission can be enhanced by increasing the smoothness of the strain barrier. We hope that our finding can shed new light on constructing graphene-based valleytronic and quantum computing devices by solely employing strain.
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Affiliation(s)
- Sake Wang
- College of Science, Jinling Institute of Technology, Nanjing 211169, People's Republic of China
| | - Hongyu Tian
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
| | - Minglei Sun
- Department of Physics and NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
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2
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Yang SJ, Choi MY, Kim CJ. Engineering Grain Boundaries in Two-Dimensional Electronic Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2203425. [PMID: 35777352 DOI: 10.1002/adma.202203425] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Revised: 06/30/2022] [Indexed: 06/15/2023]
Abstract
Engineering the boundary structures in 2D materials provides an unprecedented opportunity to program the physical properties of the materials with extensive tunability and realize innovative devices with advanced functionalities. However, structural engineering technology is still in its infancy, and creating artificial boundary structures with high reproducibility remains difficult. In this review, various emergent properties of 2D materials with different grain boundaries, and the current techniques to control the structures, are introduced. The remaining challenges for scalable and reproducible structure control and the outlook on the future directions of the related techniques are also discussed.
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Affiliation(s)
- Seong-Jun Yang
- Center for Epitaxial van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, Gyeongbuk, 37673, Republic of Korea
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk, 37673, Republic of Korea
| | - Min-Yeong Choi
- Center for Epitaxial van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, Gyeongbuk, 37673, Republic of Korea
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk, 37673, Republic of Korea
| | - Cheol-Joo Kim
- Center for Epitaxial van der Waals Quantum Solids, Institute for Basic Science (IBS), Pohang, Gyeongbuk, 37673, Republic of Korea
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk, 37673, Republic of Korea
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3
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Tian H, Ren C, Wang S. Valleytronics in two-dimensional materials with line defect. NANOTECHNOLOGY 2022; 33:212001. [PMID: 35105824 DOI: 10.1088/1361-6528/ac50f2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 02/01/2022] [Indexed: 06/14/2023]
Abstract
The concept of valley originates from two degenerate but nonequivalent energy bands at the local minimum in the conduction band or local maximum in the valence band. Manipulating the valley states for information storage and processing develops a brand-new electronics-valleytronics. Broken inversion symmetry is a necessary condition to produce pure valley currents. The polycrystalline two-dimensional materials (graphene, silicene, monolayer group-VI transition metal dichalcogenides, etc) with pristine grains stitched together by disordered grain boundaries (GBs) are the natural inversion-symmetry-broken systems and the candidates in the field of valleytronics. Different from their pristine forms, the Dirac valleys on both sides of GBs are mismatched in the momentum space and induce peculiar valley transport properties across the GBs. In this review, we systematically demonstrate the fundamental properties of valley degree of freedom across mostly studied and experimentally feasible polycrystalline structure-the line defect, and the manipulation strategies with electrical, magnetic and mechanical methods to realize the valley polarization. We also introduce an effective numerical method, the non-equilibrium Green's function technique, to tackle the valley transport issues in the line defect systems. The present challenges and the perspective on the further investigations of the line defect in valleytronics are also summarized.
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Affiliation(s)
- Hongyu Tian
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
| | - Chongdan Ren
- Department of Physics, Zunyi Normal College, Zunyi 563002, People's Republic of China
| | - Sake Wang
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
- College of Science, Jinling Institute of Technology, Nanjing 211169, People's Republic of China
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4
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Wolf TMR, Zilberberg O, Blatter G, Lado JL. Spontaneous Valley Spirals in Magnetically Encapsulated Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 126:056803. [PMID: 33605752 DOI: 10.1103/physrevlett.126.056803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Accepted: 01/07/2021] [Indexed: 06/12/2023]
Abstract
Van der Waals heterostructures provide a rich platform for emergent physics due to their tunable hybridization of layers, orbitals, and spin. Here, we find that twisted bilayer graphene stacked between antialigned ferromagnetic insulators can feature flat electronic bands due to the interplay between twist, exchange proximity, and spin-orbit coupling. These flat bands are nearly degenerate in valley only and are effectively described by a triangular superlattice model. At half filling, we find that interactions induce spontaneous valley correlations that favor spiral order and derive a low-energy valley-Heisenberg model with symmetric and antisymmetric exchange couplings. We also show how electric interlayer bias broadens the bands and tunes these couplings. Our results put forward magnetic van der Waals heterostructures as a platform to explore valley-correlated states.
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Affiliation(s)
- Tobias M R Wolf
- Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland
| | - Oded Zilberberg
- Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland
| | - Gianni Blatter
- Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland
| | - Jose L Lado
- Department of Applied Physics, Aalto University, 00076 Aalto, Espoo, Finland
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5
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Sarkar AS, Stratakis E. Recent Advances in 2D Metal Monochalcogenides. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2020; 7:2001655. [PMID: 33173730 PMCID: PMC7610304 DOI: 10.1002/advs.202001655] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 07/24/2020] [Indexed: 06/11/2023]
Abstract
The family of emerging low-symmetry and structural in-plane anisotropic two-dimensional (2D) materials has been expanding rapidly in recent years. As an important emerging anisotropic 2D material, the black phosphorene analog group IVA-VI metal monochalcogenides (MMCs) have been surged recently due to their distinctive crystalline symmetries, exotic in-plane anisotropic electronic and optical response, earth abundance, and environmentally friendly characteristics. In this article, the recent research advancements in the field of anisotropic 2D MMCs are reviewed. At first, the unique wavy crystal structures together with the optical and electronic properties of such materials are discussed. The Review continues with the various methods adopted for the synthesis of layered MMCs including micromechanical and liquid phase exfoliation as well as physical vapor deposition. The last part of the article focuses on the application of the structural anisotropic response of 2D MMCs in field effect transistors, photovoltaic cells nonlinear optics, and valleytronic devices. Besides presenting the significant research in the field of this emerging class of 2D materials, this Review also delineates the existing limitations and discusses emerging possibilities and future prospects.
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Affiliation(s)
- Abdus Salam Sarkar
- Institute of Electronic Structure and LaserFoundation for Research and Technology‐HellasHeraklionCrete700 13Greece
| | - Emmanuel Stratakis
- Institute of Electronic Structure and LaserFoundation for Research and Technology‐HellasHeraklionCrete700 13Greece
- Physics DepartmentUniversity of CreteHeraklionCrete710 03Greece
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6
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Ren CD, Lu WT, Zhou BH, Li YF, Li DY, Wang SK, Tian HY. Controllable valley filter in graphene topological line defect with magnetic field. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:365302. [PMID: 32353831 DOI: 10.1088/1361-648x/ab8ec9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 04/30/2020] [Indexed: 06/11/2023]
Abstract
The extended line defect of graphene is an extraordinary candidate in valleytronics while the high valley polarization can only occur for electrons with high incidence angles which brings about tremendous challenges to experimental realization. In this paper, we propose a novel quantum mechanism to filter one conical valley state in the line defect of graphene by applying a local magnetic field. It is found that due to the movement of the Dirac points, the transmission profiles of the two valleys are shifted along the injection-angle axis at the same pace, resulting in the peak transmission of one valley state being reduced drastically while remaining unaffected for the other valley state, which induces nearly perfect valley polarization. The valley polarization effect can occur for all the incident angle and plays a key role in graphene valleytronics.
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Affiliation(s)
- C D Ren
- Department of Physics, Zunyi Normal College, Zunyi 563002, People's Republic of China
| | - W T Lu
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
| | - B H Zhou
- Department of Physics, Shaoyang University, Shaoyang 422001, People's Republic of China
| | - Y F Li
- School of Mechanical & Vehicle Engineering, Linyi University, Linyi 276005, People's Republic of China
| | - D Y Li
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
| | - S K Wang
- College of Science, Jinling Institute of Technology, Nanjing 211169, People's Republic of China
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
| | - H Y Tian
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
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7
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Computational Atomistic Modeling in Carbon Flatland and Other 2D Nanomaterials. APPLIED SCIENCES-BASEL 2020. [DOI: 10.3390/app10051724] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
As in many countries, the rise of nanosciences in Belgium has been triggered in the eighties in the one hand, by the development of scanning tunneling and atomic force microscopes offering an unprecedented possibility to visualize and manipulate the atoms, and in the other hand, by the synthesis of nano-objects in particular carbon nanostructures such as fullerene and nanotubes. Concomitantly, the increasing calculating power and the emergence of computing facilities together with the development of DFT-based ab initio softwares have brought to nanosciences field powerful simulation tools to analyse and predict properties of nano-objects. Starting with 0D and 1D nanostructures, the floor is now occupied by the 2D materials with graphene being the bow of this 2D ship. In this review article, some specific examples of 2D systems has been chosen to illustrate how not only density functional theory (DFT) but also tight-binding (TB) techniques can be daily used to investigate theoretically the electronic, phononic, magnetic, and transport properties of these atomically thin layered materials.
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8
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Yu ZM, Guan S, Sheng XL, Gao W, Yang SA. Valley-Layer Coupling: A New Design Principle for Valleytronics. PHYSICAL REVIEW LETTERS 2020; 124:037701. [PMID: 32031831 DOI: 10.1103/physrevlett.124.037701] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Indexed: 06/10/2023]
Abstract
The current valleytronics research is based on the paradigm of time-reversal-connected valleys in two-dimensional (2D) hexagonal materials, which forbids the fully electric generation of valley polarization by a gate field. Here, we go beyond the existing paradigm to explore 2D systems with a novel valley-layer coupling (VLC) mechanism, where the electronic states in the emergent valleys have a valley-contrasted layer polarization. The VLC enables a direct coupling between a valley and a gate electric field. We analyze the symmetry requirements for a system to host VLC, demonstrate our idea via first-principles calculations and model analysis of a concrete 2D material example, and show that an electric, continuous, wide-range, and switchable control of valley polarization can be achieved by VLC. Furthermore, we find that systems with VLC can exhibit other interesting physics, such as valley-contrasting linear dichroism and optical selection of the valley and the electric polarization of interlayer excitons. Our finding opens a new direction for valleytronics and 2D materials research.
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Affiliation(s)
- Zhi-Ming Yu
- Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems, and School of Physics, Beijing Institute of Technology, Beijing 100081, China
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Shan Guan
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Xian-Lei Sheng
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
- Department of Physics, Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education), Beihang University, Beijing 100191, China
| | - Weibo Gao
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
- The Photonics Institute and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
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9
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Nguyen VH, Charlier JC. Aharonov-Bohm interferences in polycrystalline graphene. NANOSCALE ADVANCES 2020; 2:256-263. [PMID: 36133971 PMCID: PMC9419533 DOI: 10.1039/c9na00542k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 11/13/2019] [Indexed: 06/14/2023]
Abstract
Aharonov-Bohm (AB) interferences in the quantum Hall regime can be achieved, provided that electrons are able to transmit between two edge channels in nanostructures. Pioneering approaches include quantum point contacts in 2DEG systems, bipolar graphene p-n junctions, and magnetic field heterostructures. In this work, defect scattering is proposed as an alternative mechanism to achieve AB interferences in polycrystalline graphene. Indeed, due to such scattering, the extended defects across the sample can act as tunneling paths connecting quantum Hall edge channels. Consequently, strong AB oscillations in the conductance are predicted in polycrystalline graphene systems with two parallel grain boundaries. In addition, this general approach is demonstrated to be applicable to nano-systems containing two graphene barriers with functional impurities and perspectively, can also be extended to similar systems of 2D materials beyond graphene.
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Affiliation(s)
- V Hung Nguyen
- Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain (UCLouvain) Chemin des étoiles 8 B-1348 Louvain-la-Neuve Belgium
| | - J-C Charlier
- Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain (UCLouvain) Chemin des étoiles 8 B-1348 Louvain-la-Neuve Belgium
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10
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Tian H, Ren C, Zhou B, Zhang S, Lu W, Li Y, Liu J. Controllable Valley Polarization Using Silicene Double Line Defects Due to Rashba Spin-Orbit Coupling. NANOSCALE RESEARCH LETTERS 2019; 14:350. [PMID: 31776825 PMCID: PMC6881494 DOI: 10.1186/s11671-019-3196-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2019] [Accepted: 10/28/2019] [Indexed: 06/10/2023]
Abstract
We theoretically investigate the valley polarization in silicene with two parallel line defects due to Rashba spin-orbit coupling (RSOC). It is found that as long as RSOC exceeds the intrinsic spin-orbit coupling (SOC), the transmission coefficients of the two valleys oscillate with the same periodicity and intensity, which consists of wide transmission peaks and zero-transmission plateaus. However, in the presence of a perpendicular electric field, the oscillation periodicity of the first valley increases, whereas that of the second valley shortens, generating the corresponding wide peak-zero plateau regions, where perfect valley polarization can be achieved. Moreover, the valley polarizability can be changed from 1 to -1 by controlling the strength of the electric field. Our findings establish a different route for generating valley-polarized current by purely electrical means and open the door for interesting applications of semiconductor valleytronics.
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Affiliation(s)
- Hongyu Tian
- School of Physics and Electronic Engineering, Linyi University, Linyi, 276005 China
| | - ChongDan Ren
- Department of Physics, Zunyi Normal University, Kweichow, 563002 China
| | - Benhu Zhou
- Department of Physics, Shaoyang University, Shaoyang, 422001 China
| | - Shaoyin Zhang
- School of Physics and Electronic Engineering, Linyi University, Linyi, 276005 China
| | - Weitao Lu
- School of Physics and Electronic Engineering, Linyi University, Linyi, 276005 China
| | - Yunfang Li
- School of Mechanical and Vehicle Engineering, Linyi University, Linyi, 276005 China
| | - Jing Liu
- Linyi University, Linyi, 276005 China
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11
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Betancur-Ocampo Y, Leyvraz F, Stegmann T. Electron Optics in Phosphorene pn Junctions: Negative Reflection and Anti-Super-Klein Tunneling. NANO LETTERS 2019; 19:7760-7769. [PMID: 31544466 DOI: 10.1021/acs.nanolett.9b02720] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Ballistic electrons in phosphorene pn junctions show optical-like phenomena. Phosphorene is modeled by a tight-binding Hamiltonian that describes its electronic structure at low energies, where the electrons behave in the armchair direction as massive Dirac Fermions and in the orthogonal zigzag direction as Schrödinger electrons. Applying the continuum approximation, we derive the electron optics laws in phosphorene pn junctions, which show very particular and unusual properties. Because of the anisotropy of the electronic structure, these laws depend strongly on the orientation of the junction with respect to the sublattice. Negative and anomalous reflection are observed for tilted junctions, whereas the typical specular reflection is found only if the junction is parallel to the zigzag or armchair edges. Moreover, omni-directional total reflection, called anti-super-Klein tunneling, is observed if the junction is parallel to the armchair edge. Applying the nonequilibrium Green's function method on the tight-binding model, we calculate numerically the current flow. The good agreement of both approaches confirms the atypical transport properties, which can be used in nanodevices to collimate and filter the electron flow or to switch its direction.
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12
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Pang J, Mendes RG, Bachmatiuk A, Zhao L, Ta HQ, Gemming T, Liu H, Liu Z, Rummeli MH. Applications of 2D MXenes in energy conversion and storage systems. Chem Soc Rev 2019; 48:72-133. [DOI: 10.1039/c8cs00324f] [Citation(s) in RCA: 978] [Impact Index Per Article: 195.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
This article provides a comprehensive review of MXene materials and their energy-related applications.
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Affiliation(s)
- Jinbo Pang
- The Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
- Dresden
- Germany
- Institute for Advanced Interdisciplinary Research (iAIR)
- University of Jinan
| | - Rafael G. Mendes
- The Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
- Dresden
- Germany
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
| | - Alicja Bachmatiuk
- The Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
- Dresden
- Germany
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
| | - Liang Zhao
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
- School of Energy
- Soochow University
- Suzhou
| | - Huy Q. Ta
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
- School of Energy
- Soochow University
- Suzhou
| | - Thomas Gemming
- The Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
- Dresden
- Germany
| | - Hong Liu
- Institute for Advanced Interdisciplinary Research (iAIR)
- University of Jinan
- Jinan 250022
- China
- State Key Laboratory of Crystal Materials
| | - Zhongfan Liu
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
- School of Energy
- Soochow University
- Suzhou
| | - Mark H. Rummeli
- The Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
- Dresden
- Germany
- Soochow Institute for Energy and Materials InnovationS (SIEMIS)
- Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province
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13
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Betancur-Ocampo Y. Controlling electron flow in anisotropic Dirac materials heterojunctions: a super-diverging lens. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:435302. [PMID: 30229742 DOI: 10.1088/1361-648x/aae28a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Ballistic heterojunctions of Dirac materials offer the opportunity of exploring optics-like phenomena in electronic systems. In this paper, a new perfect lens through special positive refraction is predicted with omnidirectional Klein tunneling of massless Dirac fermions. The novel optics component called a super-diverging lens (SDL) is the counterpart of a Veselago lens (VL). The use of SDL and VL creates a device that simulates the ocular vision. This atypical refraction is due to electrons obeying different Snell's laws of pseudo-spin and group velocity in heterojunctions with elliptical Dirac cones. These findings pave the way for an electron elliptical Dirac optics and open up new possibilities for the guiding of electrons.
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Affiliation(s)
- Y Betancur-Ocampo
- Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico. Departamento de Físca Aplicada, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 73 Cordemex 97310 Mérida, Yucatán, Mexico
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14
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Dechamps S, Nguyen VH, Charlier JC. Ab initio quantum transport in polycrystalline graphene. NANOSCALE 2018; 10:7759-7768. [PMID: 29658557 DOI: 10.1039/c8nr00289d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Synthesis techniques such as chemical vapor deposition yield graphene in polycrystalline flakes where single-crystal domains are separated by grain boundaries (GBs) of irregular shape. These structural defects are mostly made up of pentagon-heptagon pairs and represent an important source of scattering, thus strongly affecting electronic mobilities in polycrystalline graphene (PG). In the present article, first-principles simulations are performed to explore charge transport through a GB in PG using the Landauer-Büttiker formalism implemented within the Green's function approach. In ideal GB configurations, electronic transport is found to depend on their topology as already suggested in the literature. However, more realistic GBs constructed out of various carbon rings and with more complex periodicities are also considered, possibly inducing leakage currents. Finally, additional realistic disorder such as vacancies, a larger inter-connectivity region and out-of plane buckling is investigated. For specific energies, charge redistribution effects related to the detailed GB topology are found to substantially alter the transmissions. Altogether, the transport gap is predicted to be inversely proportional to the smallest significant periodic pattern and nearly independent of the interface configuration.
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Affiliation(s)
- Samuel Dechamps
- Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Chemin des étoiles 8, B-1348 Louvain-la-Neuve, Belgium.
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15
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Tian H, Wang J. Spatial valley separation in strained graphene pn junction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:385401. [PMID: 28820742 DOI: 10.1088/1361-648x/aa8251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Valleytronics in analogy to spintronics aims to use the electron valley degree of freedom to carry and manipulate information, and one of urgent tasks in this field is to generate valley-polarized electrons. In this work, we propose using the electron focusing effect in a strained graphene pn junction to separate valleys spatially through a beam of valley-unpolarized electrons, since the strain-induced pseudo-gauge potentials are opposite for K and [Formula: see text] valleys and severely affect the trajectories of K and [Formula: see text] electron propagation. We numerically simulate this valley-separated Veselago lens effect in a lattice model and demonstrate that pseudo-gauge potentials can efficiently control valley separation patterns.
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Affiliation(s)
- HongYu Tian
- School of Physics and Electronic Engineering, Linyi University, Linyi 276005, People's Republic of China
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16
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Wang JJ, Liu S, Wang J, Liu JF. Valley filter and valve effect by strong electrostatic potentials in graphene. Sci Rep 2017; 7:10236. [PMID: 28860548 PMCID: PMC5579226 DOI: 10.1038/s41598-017-10460-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 08/08/2017] [Indexed: 11/23/2022] Open
Abstract
We report a theoretical study on the valley-filter and valley-valve effects in the monolayer graphene system by using electrostatic potentials, which are assumed to be electrically controllable. Based on a lattice model, we find that a single extremely strong electrostatic-potential barrier, with its strength exceeding the hopping energy of electrons, will significantly block one valley but allow the opposite valley flowing in the system, and this is dependent on the sign of the potential barrier as well as the flowing direction of electrons. In a valley-valve device composed of two independent potential barriers, the valley-valve efficiency can even amount to 100% that the electronic current is entirely prohibited or allowed by reversing the sign of one of potential barriers. The physics origin is attributed to the valley mixing effect in the strong potential barrier region. Our findings provide a simple electric way of controlling the valley transport in the monolayer graphene system.
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Affiliation(s)
- Juan Juan Wang
- School of Physics, Southeast University, Nanjing, 210096, China
| | - Su Liu
- School of Physics, Southeast University, Nanjing, 210096, China
| | - Jun Wang
- School of Physics, Southeast University, Nanjing, 210096, China.
| | - Jun-Feng Liu
- Department of Physics, South University of Science and Technology of China, Shenzhen, 518055, China.
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