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Chakraborti H, Gorini C, Knothe A, Liu MH, Makk P, Parmentier FD, Perconte D, Richter K, Roulleau P, Sacépé B, Schönenberger C, Yang W. Electron wave and quantum optics in graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:393001. [PMID: 38697131 DOI: 10.1088/1361-648x/ad46bc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2023] [Accepted: 05/01/2024] [Indexed: 05/04/2024]
Abstract
In the last decade, graphene has become an exciting platform for electron optical experiments, in some aspects superior to conventional two-dimensional electron gases (2DEGs). A major advantage, besides the ultra-large mobilities, is the fine control over the electrostatics, which gives the possibility of realising gap-less and compact p-n interfaces with high precision. The latter host non-trivial states,e.g., snake states in moderate magnetic fields, and serve as building blocks of complex electron interferometers. Thanks to the Dirac spectrum and its non-trivial Berry phase, the internal (valley and sublattice) degrees of freedom, and the possibility to tailor the band structure using proximity effects, such interferometers open up a completely new playground based on novel device architectures. In this review, we introduce the theoretical background of graphene electron optics, fabrication methods used to realise electron-optical devices, and techniques for corresponding numerical simulations. Based on this, we give a comprehensive review of ballistic transport experiments and simple building blocks of electron optical devices both in single and bilayer graphene, highlighting the novel physics that is brought in compared to conventional 2DEGs. After describing the different magnetic field regimes in graphene p-n junctions and nanostructures, we conclude by discussing the state of the art in graphene-based Mach-Zender and Fabry-Perot interferometers.
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Affiliation(s)
| | - Cosimo Gorini
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette, France
| | - Angelika Knothe
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Ming-Hao Liu
- Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan 70101, Taiwan
| | - Péter Makk
- Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3., Budapest H-1111, Hungary
- MTA-BME Correlated van der Waals Structures Momentum Research Group, Műegyetem rkp. 3., Budapest H-1111, Hungary
| | | | - David Perconte
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Preden Roulleau
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette, France
| | - Benjamin Sacépé
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
| | | | - Wenmin Yang
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
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Han JH, Kim JJ, Leem YC, Kim SJ, Kwak W, Jeong WL, Cho B, Lee DS, Park SJ. Improved efficiency of InGaN/GaN light-emitting diodes with perpendicular magnetic field gradients. OPTICS EXPRESS 2019; 27:36708-36716. [PMID: 31873444 DOI: 10.1364/oe.27.036708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 11/03/2019] [Indexed: 06/10/2023]
Abstract
The effect of magnetic fields on the optical output power of flip-chip light-emitting diodes (LEDs) with InGaN/GaN multiple quantum wells (MQWs) was investigated. Films and circular disks comprising ferromagnetic cobalt/platinum (Co/Pt) multilayers were deposited on a p-ohmic reflector to apply magnetic fields in the direction perpendicular to the MQWs of the LEDs. At an injection current of 20 mA, the ferromagnetic Co/Pt multilayer film increased the optical output power of the LED by 20% compared to an LED without a ferromagnetic Co/Pt multilayer. Furthermore, the optical output power of the LED with circular disks was 40% higher at 20 mA than the output of the LED with a film. The increase of the optical output power of the LEDs featuring ferromagnetic Co/Pt multilayers is attributed to the magnetic field gradient in the MQWs, which increases the carrier path in the MQWs. The time-resolved photoluminescence measurement indicates that the improvement of optical output power is owing to an enhanced radiative recombination rate of the carriers in the MQWs as a result of the magnetic field gradient from the ferromagnetic Co/Pt multilayer.
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Han JH, Kim NY, Kim SJ, Kwak W, Cho B, Park SJ, Lee DS. Magnetically enhanced luminescence of CdSe/ZnS quantum dot light-emitting diodes using circular ferromagnetic Co/Pt multilayer disks. OPTICS EXPRESS 2019; 27:36601-36610. [PMID: 31873435 DOI: 10.1364/oe.27.036601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 11/05/2019] [Indexed: 06/10/2023]
Abstract
We investigate the effect of a magnetic field on red, green, and blue CdSe/ZnS quantum dot light-emitting diodes (QDLEDs). Circular multilayer ferromagnetic cobalt/platinum (Co/Pt) disks are deposited on a MgF2 layer covering an Al electrode, and a perpendicular magnetic field is applied to the QDs in the active layer. Carriers injected into the active layer are then trapped and efficiently recombined inside the QDs because of strong carrier localization caused by the perpendicular magnetic field. The luminescence of the QDLEDs in the multilayer increases by 33.31% at 7.5 V, 22.34% at 7.5 V, and 16.73% at 7.0 V compared with that of QDLEDs without the multilayer. The time-resolved photoluminescence of all the QDLEDs also indicates that their increased luminescence results from improved radiative recombination through the stronger carrier localization in the QDs.
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Electron collimator in Weyl semimetals with periodic magnetic barriers. Sci Rep 2019; 9:10947. [PMID: 31358800 PMCID: PMC6662839 DOI: 10.1038/s41598-019-47334-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 07/11/2019] [Indexed: 11/09/2022] Open
Abstract
We investigate theoretically the effect of periodic magnetic barriers on the transport for a Weyl semimetal. We find that there are momentum and spin filtering tunneling behaviors, which is controlled by the numbers of the magnetic barriers. For the tunneling through periodic square-shaped magnetic barriers, the transmission is angular φ asymmetry, and the asymmetrical transmission probability becomes more pronounced with increasing the superlattice number n. However, the transmission is symmetric with respect to angle γ, and the window of the transmission become more and more narrower with increasing the number of barriers, i.e., the collimator behavior. This feature comes from the electron Fabry-Pérot modes among the barriers. We find that the constructive interference of the backscattering amplitudes suppress transmissions, and consequently form the minigaps of the transmission. The transmission can be switched on/off by tuning the incident energies and angles, the heights and numbers of the magnetic barriers, and result in the interesting collimator behavior.
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Jin D, Xia Y, Christensen T, Freeman M, Wang S, Fong KY, Gardner GC, Fallahi S, Hu Q, Wang Y, Engel L, Xiao ZL, Manfra MJ, Fang NX, Zhang X. Topological kink plasmons on magnetic-domain boundaries. Nat Commun 2019; 10:4565. [PMID: 31594922 PMCID: PMC6783483 DOI: 10.1038/s41467-019-12092-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Accepted: 07/31/2019] [Indexed: 11/09/2022] Open
Abstract
Two-dimensional topological materials bearing time reversal-breaking magnetic fields support protected one-way edge modes. Normally, these edge modes adhere to physical edges where material properties change abruptly. However, even in homogeneous materials, topology still permits a unique form of edge modes – kink modes – residing at the domain boundaries of magnetic fields within the materials. This scenario, despite being predicted in theory, has rarely been demonstrated experimentally. Here, we report our observation of topologically-protected high-frequency kink modes – kink magnetoplasmons (KMPs) – in a GaAs/AlGaAs two-dimensional electron gas (2DEG) system. These KMPs arise at a domain boundary projected from an externally-patterned magnetic field onto a uniform 2DEG. They propagate unidirectionally along the boundary, protected by a difference of gap Chern numbers (\documentclass[12pt]{minimal}
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\begin{document}$$\pm1$$\end{document}±1) in the two domains. They exhibit large tunability under an applied magnetic field or gate voltage, and clear signatures of nonreciprocity even under weak-coupling to evanescent photons. Topological kink modes are peculiar edge excitations that take place at domain boundaries of magnetic fields inside homogeneous materials. Here, the authors experimentally observe kink magnetoplasmons in a 2D electron gas using custom-shaped strong permanent magnets on top of a GaAs/AlGaAs heterojunction.
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Affiliation(s)
- Dafei Jin
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA.,Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - Yang Xia
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA
| | - Thomas Christensen
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Matthew Freeman
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA
| | - Siqi Wang
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA
| | - King Yan Fong
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA
| | - Geoffrey C Gardner
- Microsoft Quantum Purdue and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, 47907, USA
| | - Saeed Fallahi
- Department of Physics and Astronomy and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, 47907, USA
| | - Qing Hu
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Yuan Wang
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA
| | - Lloyd Engel
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA
| | - Zhi-Li Xiao
- Material Science Division, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - Michael J Manfra
- Microsoft Quantum Purdue, Department of Physics and Astronomy, Birck Nanotechnology Center, Schools of Electrical and Computer Engineering and Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Nicholas X Fang
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Xiang Zhang
- Nanoscale Science and Engineering Center, University of California, Berkeley, CA, 94706, USA. .,Faculties of Sciences and Engineering University of Hong Kong, Hong Kong SAR, PR, China.
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6
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Yesilyurt C, Siu ZB, Tan SG, Liang G, Yang SA, Jalil MBA. Electrically tunable valley polarization in Weyl semimetals with tilted energy dispersion. Sci Rep 2019; 9:4480. [PMID: 30872691 PMCID: PMC6418200 DOI: 10.1038/s41598-019-40947-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 02/18/2019] [Indexed: 11/16/2022] Open
Abstract
Tunneling transport across electrical potential barriers in Weyl semimetals with tilted energy dispersion is investigated. We report that the electrons around different valleys experience opposite direction refractions at the barrier interface when the energy dispersion is tilted along one of the transverse directions. Chirality dependent refractions at the barrier interface polarize the Weyl fermions in angle-space according to their valley index. A real magnetic barrier configuration is used to select allowed transmission angles, which results in electrically controllable and switchable valley polarization. Our findings may pave the way for experimental investigation of valley polarization, as well as valleytronic and electron optic applications in Weyl semimetals.
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Affiliation(s)
- Can Yesilyurt
- Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Republic of Singapore.
| | - Zhuo Bin Siu
- Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Republic of Singapore
| | - Seng Ghee Tan
- Department of Optoelectric Physics, Chinese Culture University, Taipei, 11114, Taiwan
| | - Gengchiau Liang
- Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Republic of Singapore
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore, 487372, Singapore
| | - Mansoor B A Jalil
- Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Republic of Singapore.
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7
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Hu X, Cheng F. Electron tunneling through double magnetic barriers in Weyl semimetals. Sci Rep 2017; 7:13633. [PMID: 29051602 PMCID: PMC5648818 DOI: 10.1038/s41598-017-12835-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 09/14/2017] [Indexed: 11/18/2022] Open
Abstract
We theoretically investigate the transport in a magnetic/normal/magetic hybrid structure on the surface of a Weyl semimetal. We find a directional-dependent tunneling which is sensitive to the magnetic field configuration and the electric gate voltage. The momentum filtering behavior becomes more significant for two-delta-function-shaped magnetic barriers. There are many Fabry-Pérot resonances in the transmission determined by the distance between the two magnetic barriers. The combined effects of the magnetic field and the electrostatic potential can enhance the difference in the transmission between the parallel and antiparallel magnetization configurations, and consequently lead to a giant magnetoresistance.
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Affiliation(s)
- Xunwu Hu
- Department of Physics and Electronic Science, Changsha University of Science and Technology, Changsha, 410004, China
| | - Fang Cheng
- Department of Physics and Electronic Science, Changsha University of Science and Technology, Changsha, 410004, China.
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8
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Yesilyurt C, Tan SG, Liang G, Jalil MBA. Klein tunneling in Weyl semimetals under the influence of magnetic field. Sci Rep 2016; 6:38862. [PMID: 27941894 PMCID: PMC5150982 DOI: 10.1038/srep38862] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 11/15/2016] [Indexed: 11/09/2022] Open
Abstract
Klein tunneling refers to the absence of normal backscattering of electrons even under the case of high potential barriers. At the barrier interface, the perfect matching of electron and hole wavefunctions enables a unit transmission probability for normally incident electrons. It is theoretically and experimentally well understood in two-dimensional relativistic materials such as graphene. Here we investigate the Klein tunneling effect in Weyl semimetals under the influence of magnetic field induced by ferromagnetic stripes placed at barrier boundaries. Our results show that the resonance of Fermi wave vector at specific barrier lengths gives rise to perfect transmission rings, i.e., three-dimensional analogue of the so-called magic transmission angles in two-dimensional Dirac semimetals. Besides, the transmission profile can be shifted by application of magnetic field in the central region, a property which may be utilized in electro-optic applications. When the applied potential is close to the Fermi level, a particular incident vector can be selected by tuning the magnetic field, thus enabling highly selective transmission of electrons in the bulk of Weyl semimetals. Our analytical and numerical calculations obtained by considering Dirac electrons in three regions and using experimentally feasible parameters can pave the way for relativistic tunneling applications in Weyl semimetals.
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Affiliation(s)
- Can Yesilyurt
- Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore
| | - Seng Ghee Tan
- Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore
- Data Storage Institute, Agency of Science, Technology and Research (A* Star), Singapore 138634, Republic of Singapore
| | - Gengchiau Liang
- Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore
| | - Mansoor B. A. Jalil
- Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore
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9
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Conductance oscillations induced by ballistic snake states in a graphene heterojunction. Nat Commun 2015; 6:6093. [PMID: 25652075 DOI: 10.1038/ncomms7093] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 12/11/2014] [Indexed: 11/08/2022] Open
Abstract
The realization of p-n junctions in graphene, combined with the gapless and chiral nature of its massless Dirac fermions has led to the observation of many intriguing phenomena such as the quantum Hall effect in the bipolar regime, Klein tunnelling and Fabry-Pérot interferences, all of which involve electronic transport across p-n junctions. Ballistic snake states propagating along the p-n junctions have been predicted to induce conductance oscillations, manifesting their twisting nature. However, transport studies along p-n junctions have so far only been performed in low mobility devices. Here, we report the observation of conductance oscillations due to ballistic snake states along a p-n interface in high-quality graphene encapsulated by hexagonal boron nitride. These snake states are exceptionally robust as they can propagate over 12 μm, limited only by the size of our sample, and survive up to at least 120 K. The ability to guide carriers over a long distance provide a crucial building block for graphene-based electron optics.
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Lu MW, Wang ZY, Chen SY, Zhang GL. Voltage-controllable spin beam splitter based on realistic magnetic-barrier nanostructure. Micron 2012. [PMID: 23182680 DOI: 10.1016/j.micron.2012.10.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We report a theoretical investigation on the Goos-Hänchen (GH) effect of spin electron beams in realistic magnetic-barrier (MB) nanostructures under an applied voltage, which can be experimentally created by lithographic patterning of ferromagnetic (FM) or superconducting films. GH shifts of spin electron beams are calculated numerically for the InAs material system, with the help of the stationary phase method. It is shown that a significant spin polarization effect can be induced by such MB nanostructures with symmetric magnetic field profiles. It also is shown that both magnitude and sign of the spin polarization is closely relative to the electric barrier (EB) produced by a constant voltage applied to the metallic FM stripe of system. These interesting properties may provide an alternative way to spin injection into the semiconductor, and such nanostructures can serve as voltage-tunable spin beam splitters.
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Affiliation(s)
- Mao-Wang Lu
- College of Science, Guilin University of Technology, Guilin 541004, People's Republic of China.
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Nogaret A. Electron dynamics in inhomogeneous magnetic fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:253201. [PMID: 21393794 DOI: 10.1088/0953-8984/22/25/253201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation.
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Affiliation(s)
- Alain Nogaret
- Department of Physics, University of Bath, Bath, UK.
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12
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Tarasov A, Hugger S, Xu H, Cerchez M, Heinzel T, Zozoulenko IV, Gasser-Szerer U, Reuter D, Wieck AD. Quantized magnetic confinement in quantum wires. PHYSICAL REVIEW LETTERS 2010; 104:186801. [PMID: 20482195 DOI: 10.1103/physrevlett.104.186801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Indexed: 05/29/2023]
Abstract
Ballistic quantum wires are exposed to longitudinal profiles of perpendicular magnetic fields composed of a spike and a homogeneous part. An asymmetric magnetoconductance peak as a function of the homogeneous magnetic field is found, comprising quantized conductance steps in the interval where the homogeneous magnetic field and the magnetic barrier have identical polarities, and a characteristic shoulder with several resonances in the interval of opposite polarities. The observations are interpreted in terms of inhomogeneous diamagnetic shifts of the quantum wire modes leading to magnetic confinement.
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Affiliation(s)
- A Tarasov
- Condensed Matter Physics Laboratory, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany
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13
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Nogaret A, Portal JC, Beere HE, Ritchie DA, Phillips C. Quantum interference of magnetic edge channels activated by intersubband optical transitions in magnetically confined quantum wires. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:025303. [PMID: 21813973 DOI: 10.1088/0953-8984/21/2/025303] [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 investigate the photoresistance of a magnetically confined quantum wire in which microwave-coupled edge channels interfere at two pinning sites in the fashion of a Mach-Zehnder interferometer. The conductance is strongly enhanced by microwave power at B = 0 and develops a complex series of oscillations when the magnetic confinement increases. Both results are quantitatively explained by the activation of forward scattering in a multimode magnetically confined quantum wire. By varying the strength of the magnetic confinement we are able to tune the phase of electrons in the arms of the interferometer. Quantum interferences which develop between pinning sites explain the oscillations of the conductance as a function of the magnetic field. A fit of the data gives the distance between pinning sites as 11 µm. This result suggests that quantum coherence is conserved over a distance three times longer than the electron mean free path.
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Affiliation(s)
- A Nogaret
- Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK
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14
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De Martino A, Dell'Anna L, Egger R. Magnetic confinement of massless Dirac fermions in graphene. PHYSICAL REVIEW LETTERS 2007; 98:066802. [PMID: 17358966 DOI: 10.1103/physrevlett.98.066802] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Indexed: 05/14/2023]
Abstract
Because of Klein tunneling, electrostatic potentials are unable to confine Dirac electrons. We show that it is possible to confine massless Dirac fermions in a monolayer graphene sheet by inhomogeneous magnetic fields. This allows one to design mesoscopic structures in graphene by magnetic barriers, e.g., quantum dots or quantum point contacts.
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Affiliation(s)
- A De Martino
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
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15
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Nogaret A. Electrically induced Raman emission from planar spin oscillator. PHYSICAL REVIEW LETTERS 2005; 94:147207. [PMID: 15904105 DOI: 10.1103/physrevlett.94.147207] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Indexed: 05/02/2023]
Abstract
We predict that two-dimensional electrons confined by a magnetic field gradient resonantly transfer energy to the electromagnetic field by a process of inverse electron spin resonance that is realized when the frequency of an open orbit equals the Larmor frequency. The calculated emission spectra show multiple peaks modulated by strong optical nonlinearities whose frequencies may be tuned by the magnetic field gradient and the electron concentration.
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Affiliation(s)
- A Nogaret
- Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom.
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16
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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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17
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Frustaglia D, Hentschel M, Richter K. Quantum transport in nonuniform magnetic fields: Aharonov-Bohm ring as a spin switch. PHYSICAL REVIEW LETTERS 2001; 87:256602. [PMID: 11736592 DOI: 10.1103/physrevlett.87.256602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2001] [Indexed: 05/23/2023]
Abstract
We study spin-dependent magnetoconductance in mesoscopic rings subject to an inhomogeneous in-plane magnetic field. We show that the polarization direction of transmitted spin-polarized electrons can be controlled via an additional magnetic flux such that spin flips are induced at half a flux quantum. This quantum interference effect is independent of the strength of the nonuniform field applied. We give an analytical explanation for one-dimensional rings and numerical results for corresponding ballistic microstructures.
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Affiliation(s)
- D Frustaglia
- Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Strasse 38, 01187 Dresden, Germany
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18
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Sim HS, Ihm G, Kim N, Chang KJ. Magnetic quantum dot: a magnetic transmission barrier and resonator. PHYSICAL REVIEW LETTERS 2001; 87:146601. [PMID: 11580664 DOI: 10.1103/physrevlett.87.146601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2001] [Indexed: 05/23/2023]
Abstract
We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B(*) and B0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B(*) is parallel or antiparallel to B0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.
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Affiliation(s)
- H S Sim
- Department of Physics, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea
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