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Lee YK, Smith JS, Cole JH. Influence of Device Geometry and Imperfections on the Interpretation of Transverse Magnetic Focusing Experiments. NANOSCALE RESEARCH LETTERS 2022; 17:31. [PMID: 35247127 PMCID: PMC8898212 DOI: 10.1186/s11671-022-03671-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 02/19/2022] [Indexed: 06/14/2023]
Abstract
Spatially separating electrons of different spins and efficiently generating spin currents are crucial steps towards building practical spintronics devices. Transverse magnetic focusing is a potential technique to accomplish both those tasks. In a material where there is significant Rashba spin-orbit interaction, electrons of different spins will traverse different paths in the presence of an external magnetic field. Experiments have demonstrated the viability of this technique by measuring conductance spectra that indicate the separation of spin-up and spin-down electrons. However the effect that the geometry of the leads has on these measurements is not well understood. By simulating an InGaAs-based transverse magnetic focusing device, we show that the resolution of features in the conductance spectra is affected by the shape, separation and width of the leads. Furthermore, the number of subbands occupied by the electrons in the leads affects the ratio between the amplitudes of the spin-split peaks in the spectra. We simulated devices with random onsite potentials and observed that transverse magnetic focusing devices are sensitive to disorder. Ultimately we show that careful choice and characterisation of device geometry are crucial for correctly interpreting the results of transverse magnetic focusing experiments.
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Affiliation(s)
- Yik Kheng Lee
- Theoretical, Computational, and Quantum Physics, School of Science, RMIT University, Melbourne, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, RMIT University, Melbourne, Australia
| | - Jackson S. Smith
- Theoretical, Computational, and Quantum Physics, School of Science, RMIT University, Melbourne, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, RMIT University, Melbourne, Australia
| | - Jared H. Cole
- Theoretical, Computational, and Quantum Physics, School of Science, RMIT University, Melbourne, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, RMIT University, Melbourne, Australia
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2
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Nonmagnetic single-molecule spin-filter based on quantum interference. Nat Commun 2019; 10:5565. [PMID: 31804498 PMCID: PMC6895237 DOI: 10.1038/s41467-019-13537-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 11/12/2019] [Indexed: 11/09/2022] Open
Abstract
Key spin transport phenomena, including magnetoresistance and spin transfer torque, cannot be activated without spin-polarized currents, in which one electron spin is dominant. At the nanoscale, the relevant length-scale for modern spintronics, spin current generation is rather limited due to unwanted contributions from poorly spin-polarized frontier states in ferromagnetic electrodes, or too short length-scales for efficient spin splitting by spin-orbit interaction and magnetic fields. Here, we show that spin-polarized currents can be generated in silver-vanadocene-silver single molecule junctions without magnetic components or magnetic fields. In some cases, the measured spin currents approach the limit of ideal ballistic spin transport. Comparison between conductance and shot-noise measurements to detailed calculations reveals a mechanism based on spin-dependent quantum interference that yields very efficient spin filtering. Our findings pave the way for nanoscale spintronics based on quantum interference, with the advantages of low sensitivity to decoherence effects and the freedom to use non-magnetic materials.
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3
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Xiong YC, Zhou WH, Li W, Huang HM, Laref A, Nan N, Zhang J, Yang JT. Emergent electronically-controllable local-field-inducer based on a molecular break-junction with magnetic radical. Phys Chem Chem Phys 2019; 21:21693-21697. [PMID: 31556898 DOI: 10.1039/c9cp04523f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Molecular spintronics devices are receiving extensive research attention, due to their potential applications as the smallest memory and logic elements. A most fundamental issue in this field lies in generating spin polarized currents. In this communication, with the aid of the celebrated Wilson's numerical renormalization group (NRG) method, we propose theoretically a novel strategy to induce a local magnetic field that only affects the strongly correlated molecule under consideration, and could easily be manipulated through purely electronic technologies. It is also demonstrated that the device may lead to bidirectional spin polarization, where perfectly polarized spin-up and -down currents could be obtained by simply adjusting the energy level of the molecule to different regions along a single direction. Our suggested model is based on a molecular break-junction with a magnetic radical. It may provide a prospective example of a magnetoelectronics device at the molecular scale, which works without an external magnetic field.
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Affiliation(s)
- Yong-Chen Xiong
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
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4
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Xiong Y, Luo S, Huang H, Ma Y, Zhang X. Exchange-dependent spin polarized transport and phase transition in a triple monomer molecule. Phys Chem Chem Phys 2019; 21:11158-11167. [PMID: 31095151 DOI: 10.1039/c9cp01350d] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular junctions contribute significantly to the fundamental understanding of the quantum information technologies in molecular spintronics. In this paper, with the aid of the state of the art numerical renormalization group method, we find a triple monomer molecule structure with strong electron-electron interactions could be a potential candidate for a multifunctional spin polarizer when an external magnetic field along the z axis is applied. It is demonstrated that the polarizing scenarios depend closely on the inter-orbital exchange couplings, and results in several kinds of spin polarizers, e.g., the unidirectional, the bidirectional, the dual, and the ternary spin polarizers. We show in detail the related phase diagram, and conclude the Zeeman effect and the charge switching for the bonding, anti-bonding and non-bonding orbitals are responsible for the spin polarizing transport. We stress even when the energy levels are chosen beyond the Kondo regime, the structure still shows a promising platform for molecular spintronics components.
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Affiliation(s)
- Yongchen Xiong
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
| | - Shijun Luo
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
| | - Haiming Huang
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
| | - Yanan Ma
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
| | - Xiong Zhang
- Advanced Functional Material and Photoelectric Technology Research Institution, School of Science, Hubei University of Automotive Technology, Shiyan 442002, People's Republic of China.
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5
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Xiong YC, Luo SJ, Zhou WH, Li W, Zhang CK. Bidirectional spin filter in a triple orbital molecule junction by tuning the magnetic field along a single direction. J Chem Phys 2019; 150:064110. [DOI: 10.1063/1.5081020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yong-Chen Xiong
- School of Science, and Advanced Functional Material and Photoelectric Technology Research Institution, Hubei University of Automotive Technology, Shiyan 442002, People’s Republic of China
| | - Shi-Jun Luo
- School of Science, and Advanced Functional Material and Photoelectric Technology Research Institution, Hubei University of Automotive Technology, Shiyan 442002, People’s Republic of China
| | - Wang-Huai Zhou
- School of Science, and Advanced Functional Material and Photoelectric Technology Research Institution, Hubei University of Automotive Technology, Shiyan 442002, People’s Republic of China
| | - Wei Li
- School of Science, and Advanced Functional Material and Photoelectric Technology Research Institution, Hubei University of Automotive Technology, Shiyan 442002, People’s Republic of China
| | - Chuan-Kun Zhang
- School of Science, and Advanced Functional Material and Photoelectric Technology Research Institution, Hubei University of Automotive Technology, Shiyan 442002, People’s Republic of China
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6
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Ho SC, Chang HJ, Chang CH, Lo ST, Creeth G, Kumar S, Farrer I, Ritchie D, Griffiths J, Jones G, Pepper M, Chen TM. Imaging the Zigzag Wigner Crystal in Confinement-Tunable Quantum Wires. PHYSICAL REVIEW LETTERS 2018; 121:106801. [PMID: 30240231 DOI: 10.1103/physrevlett.121.106801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Revised: 07/03/2018] [Indexed: 06/08/2023]
Abstract
The existence of Wigner crystallization, one of the most significant hallmarks of strong electron correlations, has to date only been definitively observed in two-dimensional systems. In one-dimensional (1D) quantum wires Wigner crystals correspond to regularly spaced electrons; however, weakening the confinement and allowing the electrons to relax in a second dimension is predicted to lead to the formation of a new ground state constituting a zigzag chain with nontrivial spin phases and properties. Here we report the observation of such zigzag Wigner crystals by use of on-chip charge and spin detectors employing electron focusing to image the charge density distribution and probe their spin properties. This experiment demonstrates both the structural and spin phase diagrams of the 1D Wigner crystallization. The existence of zigzag spin chains and phases which can be electrically controlled in semiconductor systems may open avenues for experimental studies of Wigner crystals and their technological applications in spintronics and quantum information.
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Affiliation(s)
- Sheng-Chin Ho
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Heng-Jian Chang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Chia-Hua Chang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Shun-Tsung Lo
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Graham Creeth
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Sanjeev Kumar
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Ian Farrer
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
- Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom
| | - David Ritchie
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Jonathan Griffiths
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Geraint Jones
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Michael Pepper
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Tse-Ming Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
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7
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Thi Thu Huong V, Tai TB, Jiang JC, Nguyen MT. Spin-polarized transport properties in some transition metal dithiolene complexes. Phys Chem Chem Phys 2017; 19:32536-32543. [PMID: 29188831 DOI: 10.1039/c7cp05962k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Spin filtering materials are of great current interest in part due to their applications in molecular electronics. In this study, we carried out a theoretical investigation on the charge transport properties of transition metal (TM) dithiolene complexes with TM = Ni, Fe and Mn by using non-equilibrium Green's function/density functional theory (NEGF-DFT) methods. The characteristics of current-voltage and spin-resolved transmission spectra pointed out that Ni complexes are non-polarized, while Fe and Mn complexes exhibit high polarization and can be regarded as excellent candidates for spin-filtering materials with high spin-filtering efficiency. These differences were rationalized on the basis of electron delocalization over the molecular junction of the partial distribution of α- and β-spin molecular projected self-consistent Hamiltonian (MPSH) orbitals, and also the first eigenchannels of molecular junctions.
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Affiliation(s)
- Vu Thi Thu Huong
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
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8
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Controlled spatial separation of spins and coherent dynamics in spin-orbit-coupled nanostructures. Nat Commun 2017; 8:15997. [PMID: 28691707 PMCID: PMC5508128 DOI: 10.1038/ncomms15997] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 05/17/2017] [Indexed: 11/08/2022] Open
Abstract
The spatial separation of electron spins followed by the control of their individual spin dynamics has recently emerged as an essential ingredient in many proposals for spin-based technologies because it would enable both of the two spin species to be simultaneously utilized, distinct from most of the current spintronic studies and technologies wherein only one spin species could be handled at a time. Here we demonstrate that the spatial spin splitting of a coherent beam of electrons can be achieved and controlled using the interplay between an external magnetic field and Rashba spin-orbit interaction in semiconductor nanostructures. The technique of transverse magnetic focusing is used to detect this spin separation. More notably, our ability to engineer the spin-orbit interactions enables us to simultaneously manipulate and probe the coherent spin dynamics of both spin species and hence their correlation, which could open a route towards spintronics and spin-based quantum information processing.
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9
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Spin filtering effect generated by the inter-subband spin-orbit coupling in the bilayer nanowire with the quantum point contact. Sci Rep 2017; 7:45346. [PMID: 28358141 PMCID: PMC5371906 DOI: 10.1038/srep45346] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 02/27/2017] [Indexed: 11/23/2022] Open
Abstract
The spin filtering effect in the bilayer nanowire with quantum point contact is investigated theoretically. We demonstrate the new mechanism of the spin filtering based on the lateral inter-subband spin-orbit coupling, which for the bilayer nanowires has been reported to be strong. The proposed spin filtering effect is explained as the joint effect of the Landau-Zener intersubband transitions caused by the hybridization of states with opposite spin (due to the lateral Rashba SO interaction) and the confinement of carriers in the quantum point contact region.
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10
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Ideal Spintronics in Molecule-Based Novel Organometallic Nanowires. Sci Rep 2015; 5:12772. [PMID: 26239021 PMCID: PMC4523865 DOI: 10.1038/srep12772] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 07/09/2015] [Indexed: 01/11/2023] Open
Abstract
With the purpose of searching for new intriguing nanomaterial for spintronics, a series of novel metalloporphyrin nanowires (M-PPNW, M = Cr, Mn, Fe, Co, Ni, Cu and Zn) and hybrid nanowires fabricated by metalloporphyrin and metal-phthalocyanine (M-PCNW) are systematically investigated by means of first-principles calculations. Our results indicate that the transition metal atoms (TMs) embedded in the frameworks distribute regularly and separately, without any trend to form clusters, thus leading to the ideally ordered spin distribution. Except for the cases embedded with Ni and Zn, the others are spin-polarized. Remarkably, the Mn-PPNW, Mn-PCNW, MnCu-PPNW, MnCr-PCNW, and MnCu-PCNW frameworks all favor the long-ranged ferromagnetic spin ordering and display half-metallic nature, which are of greatest interest and importance for electronics and spintronics. The predicted Curie temperature for the Mn-PCNW is about 150 K. In addition, it is found that the discrepancy in magnetic coupling for these materials is related to the competition mechanisms of through-bond and through-space exchange interactions. In the present work, we propose not only two novel sets of 1D frameworks with appealing magnetic properties, but also a new strategy in obtaining the half-metallic materials by the combination of different neighboring TMs.
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11
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Goswami S, Mulazimoglu E, Vandersypen LMK, Caviglia AD. Nanoscale electrostatic control of oxide interfaces. NANO LETTERS 2015; 15:2627-2632. [PMID: 25749273 DOI: 10.1021/acs.nanolett.5b00216] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We develop a robust and versatile platform to define nanostructures at oxide interfaces via patterned top gates. Using LaAlO3/SrTiO3 as a model system, we demonstrate controllable electrostatic confinement of electrons to nanoscale regions in the conducting interface. The excellent gate response, ultralow leakage currents, and long-term stability of these gates allow us to perform a variety of studies in different device geometries from room temperature down to 50 mK. Using a split-gate device we demonstrate the formation of a narrow conducting channel whose width can be controllably reduced via the application of appropriate gate voltages. We also show that a single narrow gate can be used to induce locally a superconducting to insulating transition. Furthermore, in the superconducting regime we see indications of a gate-voltage controlled Josephson effect.
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Affiliation(s)
- Srijit Goswami
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
| | - Emre Mulazimoglu
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
| | - Lieven M K Vandersypen
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
| | - Andrea D Caviglia
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
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12
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Guimarães MHD, Zomer PJ, Vera-Marun IJ, van Wees BJ. Spin-dependent quantum interference in nonlocal graphene spin valves. NANO LETTERS 2014; 14:2952-2956. [PMID: 24762101 DOI: 10.1021/nl501087r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Up to date, all spin transport experiments on graphene were done in a semiclassical regime, disregarding quantum transport properties such as phase coherence and interference. Here we show that in a quantum coherent graphene nanostructure the nonlocal voltage is strongly modulated. Using nonlocal measurements, we separate the signal in spin-dependent and spin-independent contributions. We show that the spin-dependent contribution is about 2 orders of magnitude larger than the spin-independent one, when corrected for the finite polarization of the electrodes. The nonlocal spin signal is not only strongly modulated but also changes polarity as a function of the applied gate voltage. By locally tuning the carrier density in the constriction via a side gate electrode we show that the constriction plays a major role in this effect. Our results show the potential of quantum coherent graphene nanostructures for the use in future spintronic devices.
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Affiliation(s)
- M H D Guimarães
- Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen , 9712 CP Groningen, The Netherlands
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13
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Chen TM, Pepper M, Farrer I, Jones GAC, Ritchie DA. All-electrical injection and detection of a spin-polarized current using 1D conductors. PHYSICAL REVIEW LETTERS 2012; 109:177202. [PMID: 23215217 DOI: 10.1103/physrevlett.109.177202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Revised: 09/06/2012] [Indexed: 06/01/2023]
Abstract
All-electrical control of spin transport in nanostructures has been the central interest and challenge of spin physics and spintronics. Here we demonstrate on-chip spin polarizing or filtering actions by driving the gate-defined one dimensional (1D) conductor, one of the simplest geometries for integrated quantum devices, away from the conventional Ohmic regime. Direct measurement of the spin polarization of the emitted current was performed when the momentum degeneracy was lifted, wherein both the 1D polarizer for spin injection and the analyzer for spin detection were demonstrated. The results showed that a configuration of gates and applied voltages can give rise to a tunable spin polarization, which has implications for the development of spintronic devices and future quantum information processing.
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Affiliation(s)
- T-M Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan.
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14
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Burke AM, Klochan O, Farrer I, Ritchie DA, Hamilton AR, Micolich AP. Extreme sensitivity of the spin-splitting and 0.7 anomaly to confining potential in one-dimensional nanoelectronic devices. NANO LETTERS 2012; 12:4495-4502. [PMID: 22830617 DOI: 10.1021/nl301566d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Quantum point contacts (QPCs) have shown promise as nanoscale spin-selective components for spintronic applications and are of fundamental interest in the study of electron many-body effects such as the 0.7 × 2e(2)/h anomaly. We report on the dependence of the 1D Landé g-factor g and 0.7 anomaly on electron density and confinement in QPCs with two different top-gate architectures. We obtain g values up to 2.8 for the lowest 1D subband, significantly exceeding previous in-plane g-factor values in AlGaAs/GaAs QPCs and approaching that in InGaAs/InP QPCs. We show that g is highly sensitive to confinement potential, particularly for the lowest 1D subband. This suggests careful management of the QPC's confinement potential may enable the high g desirable for spintronic applications without resorting to narrow-gap materials such as InAs or InSb. The 0.7 anomaly and zero-bias peak are also highly sensitive to confining potential, explaining the conflicting density dependencies of the 0.7 anomaly in the literature.
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Affiliation(s)
- A M Burke
- School of Physics, University of New South Wales, Sydney NSW 2052, Australia.
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15
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Micolich AP. What lurks below the last plateau: experimental studies of the 0.7 × 2e(2)/h conductance anomaly in one-dimensional systems. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:443201. [PMID: 21997403 DOI: 10.1088/0953-8984/23/44/443201] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The integer quantised conductance of one-dimensional electron systems is a well-understood effect of quantum confinement. A number of fractionally quantised plateaus are also commonly observed. They are attributed to many-body effects, but their precise origin is still a matter of debate, having attracted considerable interest over the past 15 years. This review reports on experimental studies of fractionally quantised plateaus in semiconductor quantum point contacts and quantum wires, focusing on the 0.7 × 2e(2)/h conductance anomaly, its analogues at higher conductances and the zero-bias peak observed in the dc source-drain bias for conductances less than 2e(2)/h.
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Affiliation(s)
- A P Micolich
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
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16
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Cho WJ, Cho Y, Min SK, Kim WY, Kim KS. Chromium Porphyrin Arrays As Spintronic Devices. J Am Chem Soc 2011; 133:9364-9. [DOI: 10.1021/ja111565w] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Woo Jong Cho
- Department of Chemistry and Department of Physics, Pohang University of Science and Technology, San 31 Pohang, Republic of Korea
| | - Yeonchoo Cho
- Department of Chemistry and Department of Physics, Pohang University of Science and Technology, San 31 Pohang, Republic of Korea
| | - Seung Kyu Min
- Department of Chemistry and Department of Physics, Pohang University of Science and Technology, San 31 Pohang, Republic of Korea
| | - Woo Youn Kim
- Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea
| | - Kwang S. Kim
- Department of Chemistry and Department of Physics, Pohang University of Science and Technology, San 31 Pohang, Republic of Korea
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17
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Hof KD, Kaiser FJ, Stallhofer M, Schuh D, Wegscheider W, Hänggi P, Kohler S, Kotthaus JP, Holleitner AW. Spatially resolved ballistic optoelectronic transport measured by quantized photocurrent spectroscopy. NANO LETTERS 2010; 10:3836-3840. [PMID: 20853822 DOI: 10.1021/nl102068v] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
GaAs-based quantum point contacts (QPCs) are exploited to spatially resolve and analyze the ballistic, nonequilibrium flow of photogenerated electrons in a nanoscale circuit. Electron-hole pairs are photogenerated in a two-dimensional electron gas (2DEG), and the resulting current through an adjacent QPC is measured as a function of the laser spot position. The transmission of photogenerated electrons through the QPC is governed by the energy dispersion and the quantized momentum values of the electron modes in the QPC.
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Affiliation(s)
- Klaus-Dieter Hof
- Fakultät für Physik and Center for NanoScience, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, D-80539 München, Germany
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18
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Abstract
This is a review on graphene quantum dots and their use as a host for spin qubits. We discuss the advantages but also the challenges to use graphene quantum dots for spin qubits as compared to the more standard materials like GaAs. We start with an overview of this young and fascinating field and then discuss gate-tunable quantum dots in detail. We calculate the bound states for three different quantum dot architectures where a bulk gap allows for confinement via electrostatic fields: (i) graphene nanoribbons with armchair boundaries, (ii) a disc in single-layer graphene, and (iii) a disc in bilayer graphene. In order for graphene quantum dots to be useful in the context of spin qubits, one needs to find reliable ways to break the valley degeneracy. This is achieved here, either by a specific termination of graphene in (i) or in (ii) and (iii) by a magnetic field, without the need of a specific boundary. We further discuss how to manipulate spin in these quantum dots and explain the mechanism of spin decoherence and relaxation caused by spin-orbit interaction in combination with electron-phonon coupling, and by hyperfine interaction with the nuclear-spin system.
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Affiliation(s)
- Patrik Recher
- Institut für Theoretische Physik und Astrophysik, University of Würzburg, Würzburg, Germany.
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19
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Ojeda JH, Pacheco M, Orellana PA. An array of quantum dots as a spin filter device by using Dicke and Fano effects. NANOTECHNOLOGY 2009; 20:434013. [PMID: 19801762 DOI: 10.1088/0957-4484/20/43/434013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In this paper we propose a new design of a spin-dependent polarizer based on a quantum dot array coupled to leads. By lifting the spin degeneracy of the carriers in the quantum dots by means of a magnetic field, Fano and Dicke effects may be used as effective means to generate spin-polarized currents. A detailed analysis of the spin-dependent transmission and polarized current as a function of the applied magnetic field and gate voltages is carried out.
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Affiliation(s)
- J H Ojeda
- Departamento de Física, Universidad Santa María, Casilla 110 V, Valparaíso, Chile
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20
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Frolov SM, Venkatesan A, Yu W, Folk JA, Wegscheider W. Electrical generation of pure spin currents in a two-dimensional electron gas. PHYSICAL REVIEW LETTERS 2009; 102:116802. [PMID: 19392226 DOI: 10.1103/physrevlett.102.116802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Indexed: 05/27/2023]
Abstract
Pure spin currents are generated and detected in micron-wide channels of a GaAs two-dimensional electron gas, using quantum point contacts in an in-plane magnetic field as injectors and detectors. The enhanced sensitivity to spin transport offered by a nonlocal measurement geometry enables accurate spin current measurements in this widely studied physical system. The polarization of the contacts is used to extract the quantum point contact g factor and provides a test for spontaneous polarization at 0.7 structure. The spin relaxation length in the channel is 30-50 microm over the magnetic field range 3-10 T, much longer than has been reported in GaAs two-dimensional electron gases but shorter than that expected from Dyakonov-Perel relaxation.
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Affiliation(s)
- S M Frolov
- Department of Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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Wang XJ, Buyanova IA, Zhao F, Lagarde D, Balocchi A, Marie X, Tu CW, Harmand JC, Chen WM. Room-temperature defect-engineered spin filter based on a non-magnetic semiconductor. NATURE MATERIALS 2009; 8:198-202. [PMID: 19219029 DOI: 10.1038/nmat2385] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 01/13/2009] [Indexed: 05/27/2023]
Abstract
Generating, manipulating and detecting electron spin polarization and coherence at room temperature is at the heart of future spintronics and spin-based quantum information technology. Spin filtering, which is a key issue for spintronic applications, has been demonstrated by using ferromagnetic metals, diluted magnetic semiconductors, quantum point contacts, quantum dots, carbon nanotubes, multiferroics and so on. This filtering effect was so far restricted to a limited efficiency and primarily at low temperatures or under a magnetic field. Here, we provide direct and unambiguous experimental proof that an electron-spin-polarized defect, such as a Ga(i) self-interstitial in dilute nitride GaNAs, can effectively deplete conduction electrons with an opposite spin orientation and can thus turn the non-magnetic semiconductor into an efficient spin filter operating at room temperature and zero magnetic field. This work shows the potential of such defect-engineered, switchable spin filters as an attractive alternative to generate, amplify and detect electron spin polarization at room temperature without a magnetic material or external magnetic fields.
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Affiliation(s)
- X J Wang
- Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
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Apel VM, Orellana PA, Pacheco M. Fano and Dicke effects in a double Rashba-ring system. NANOTECHNOLOGY 2008; 19:355202. [PMID: 21828835 DOI: 10.1088/0957-4484/19/35/355202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The electronic transport in a system of two quantum rings side-coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We derived analytical expressions for the conductance and spin polarization when the rings are threaded by magnetic fluxes with Rashba spin-orbit interaction. We show that by using the Fano and Dicke effects this system can be used as an efficient spin filter even for small spin-orbit interaction and small values of magnetic fluxes. We compare the spin-dependent polarization of this design and the polarization obtained with one ring side-coupled to a quantum ring. As a main result, we find better spin polarization capabilities as compared to the one-ring design.
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Affiliation(s)
- V M Apel
- Departamento de Física, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile
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Orellana PA, Amado M, Domínguez-Adame F. Fano-Rashba effect in quantum dots. NANOTECHNOLOGY 2008; 19:195401. [PMID: 21825714 DOI: 10.1088/0957-4484/19/19/195401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We consider the electronic transport through a Rashba quantum dot coupled to ferromagnetic leads. We show that the interference of localized electron states with resonant electron states leads to the appearance of the Fano-Rashba effect. This effect occurs due to the interference of bound levels of spin-polarized electrons with the continuum of electronic states with an opposite spin polarization. We investigate this Fano-Rashba effect as a function of the applied magnetic field and Rashba spin-orbit coupling.
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Affiliation(s)
- P A Orellana
- Departamento de Física, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile
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Abstract
In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin dependence because the conduction channels of only one spin component align with the chemical potential of the leads, resulting in a spin polarized electric current. The possibility to create such a spin polarized current is investigated here with the organometallic moiety cobaltocene. According to our calculations, cobaltocene contacted with gold electrodes acts as a robust spin filter: Applying a voltage less than 0.2 V causes the current of one spin component crossing the molecular bridge to be two orders of magnitude larger than the other. We address the key issue of sensitivity to molecule-lead geometry by showing that a weak barrier generated by CH(2) groups between the cobaltocene and the leads is crucial in reducing the sensitivity to the contact geometry while only reducing the current modestly. These results suggest cobaltocene as a robust basic building block for molecular spintronics.
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Affiliation(s)
- Rui Liu
- Department of Chemistry, Duke University, Durham, NC 27708-0354, USA
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Novikova GV, Moshkov IE, Los DA. Protein sensors and transducers of cold and osmotic stress in cyanobacteria and plants. Mol Biol 2007. [DOI: 10.1134/s0026893307030089] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Quantum Entanglement and Teleportation of Quantum-Dot States in Microcavities. E-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY 2007. [DOI: 10.1380/ejssnt.2007.51] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Affiliation(s)
- J Carlos Egues
- Department of Physics and Informatics, Institute of Physics of São Carlos, University of São Paulo, São Carlos 13560-970, Brazil.
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Wróbel J, Dietl T, Lusakowski A, Grabecki G, Fronc K, Hey R, Ploog KH, Shtrikman H. Spin filtering in a hybrid ferromagnetic-semiconductor microstructure. PHYSICAL REVIEW LETTERS 2004; 93:246601. [PMID: 15697839 DOI: 10.1103/physrevlett.93.246601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Indexed: 05/24/2023]
Abstract
We fabricated a hybrid structure in which cobalt and permalloy micromagnets produce a local in-plane spin-dependent potential barrier for high-mobility electrons at the GaAs/AlGaAs interface. Spin effects are observed in ballistic transport in the range of tens of mT of the external field and are attributed to switching between Zeeman and Stern-Gerlach modes--the former dominating at low electron densities.
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Affiliation(s)
- J Wróbel
- Institute of Physics, Polish Academy of Sciences, al Lotników 32/46, 02-668 Warszawa, Poland
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Rokhinson LP, Larkina V, Lyanda-Geller YB, Pfeiffer LN, West KW. Spin separation in cyclotron motion. PHYSICAL REVIEW LETTERS 2004; 93:146601. [PMID: 15524823 DOI: 10.1103/physrevlett.93.146601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2004] [Indexed: 05/24/2023]
Abstract
Charged carriers with different spin states are spatially separated in a two-dimensional hole gas. Because of strong spin-orbit interaction, holes at the Fermi energy in GaAs have different momenta for two possible spin states traveling in the same direction, and, correspondingly, different cyclotron orbits in a weak magnetic field. Two point contacts, acting as a monochromatic source of ballistic holes and a narrow detector arranged in the magnetic focusing geometry are demonstrated to work as a tunable spin filter.
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Affiliation(s)
- L P Rokhinson
- Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA.
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Elzerman JM, Hanson R, Willems Van Beveren LH, Witkamp B, Vandersypen LMK, Kouwenhoven LP. Single-shot read-out of an individual electron spin in a quantum dot. Nature 2004; 430:431-5. [PMID: 15269762 DOI: 10.1038/nature02693] [Citation(s) in RCA: 355] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2004] [Accepted: 05/25/2004] [Indexed: 11/09/2022]
Abstract
Spin is a fundamental property of all elementary particles. Classically it can be viewed as a tiny magnetic moment, but a measurement of an electron spin along the direction of an external magnetic field can have only two outcomes: parallel or anti-parallel to the field. This discreteness reflects the quantum mechanical nature of spin. Ensembles of many spins have found diverse applications ranging from magnetic resonance imaging to magneto-electronic devices, while individual spins are considered as carriers for quantum information. Read-out of single spin states has been achieved using optical techniques, and is within reach of magnetic resonance force microscopy. However, electrical read-out of single spins has so far remained elusive. Here we demonstrate electrical single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot. We use spin-to-charge conversion of a single electron confined in the dot, and detect the single-electron charge using a quantum point contact; the spin measurement visibility is approximately 65%. Furthermore, we observe very long single-spin energy relaxation times (up to approximately 0.85 ms at a magnetic field of 8 T), which are encouraging for the use of electron spins as carriers of quantum information.
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Affiliation(s)
- J M Elzerman
- Kavli Institute of Nanoscience Delft and ERATO Mesoscopic Correlation Project, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
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Watson SK, Potok RM, Marcus CM, Umansky V. Experimental realization of a quantum spin pump. PHYSICAL REVIEW LETTERS 2003; 91:258301. [PMID: 14754164 DOI: 10.1103/physrevlett.91.258301] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2003] [Indexed: 05/24/2023]
Abstract
We demonstrate the operation of a quantum spin pump based on cyclic radio-frequency excitation of a GaAs quantum dot, including the ability to pump pure spin without pumping charge. The device takes advantage of bidirectional mesoscopic fluctuations of pumped current, made spin dependent by the application of an in-plane Zeeman field. Spin currents are measured by placing the pump in a focusing geometry with a spin-selective collector.
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Affiliation(s)
- Susan K Watson
- Department of Physics, Middlebury College, Middlebury, Vermont 05753, USA
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Potok RM, Folk JA, Marcus CM, Umansky V, Hanson M, Gossard AC. Spin and polarized current from Coulomb blockaded quantum dots. PHYSICAL REVIEW LETTERS 2003; 91:016802. [PMID: 12906563 DOI: 10.1103/physrevlett.91.016802] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2003] [Indexed: 05/24/2023]
Abstract
We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.
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Affiliation(s)
- R M Potok
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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