1
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Greenaway MT, Kumaravadivel P, Wengraf J, Ponomarenko LA, Berdyugin AI, Li J, Edgar JH, Kumar RK, Geim AK, Eaves L. Graphene's non-equilibrium fermions reveal Doppler-shifted magnetophonon resonances accompanied by Mach supersonic and Landau velocity effects. Nat Commun 2021; 12:6392. [PMID: 34737289 PMCID: PMC8568928 DOI: 10.1038/s41467-021-26663-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 10/15/2021] [Indexed: 11/21/2022] Open
Abstract
Oscillatory magnetoresistance measurements on graphene have revealed a wealth of novel physics. These phenomena are typically studied at low currents. At high currents, electrons are driven far from equilibrium with the atomic lattice vibrations so that their kinetic energy can exceed the thermal energy of the phonons. Here, we report three non-equilibrium phenomena in monolayer graphene at high currents: (i) a “Doppler-like” shift and splitting of the frequencies of the transverse acoustic (TA) phonons emitted when the electrons undergo inter-Landau level (LL) transitions; (ii) an intra-LL Mach effect with the emission of TA phonons when the electrons approach supersonic speed, and (iii) the onset of elastic inter-LL transitions at a critical carrier drift velocity, analogous to the superfluid Landau velocity. All three quantum phenomena can be unified in a single resonance equation. They offer avenues for research on out-of-equilibrium phenomena in other two-dimensional fermion systems. Magneto-oscillations have revealed many interesting phenomena in graphene and quantum Hall systems, but they are typically measured at low currents and in equilibrium. Here, the authors report several non-equilibrium quantum effects observed in magneto-oscillations in graphene at high currents.
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Affiliation(s)
- M T Greenaway
- Department of Physics, Loughborough University, Loughborough, LE11 3TU, UK. .,School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
| | - P Kumaravadivel
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK
| | - J Wengraf
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.,Department of Physics, University of Lancaster, Lancaster, LA1 4YW, UK
| | - L A Ponomarenko
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.,Department of Physics, University of Lancaster, Lancaster, LA1 4YW, UK
| | - A I Berdyugin
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK
| | - J Li
- Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - J H Edgar
- Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - R Krishna Kumar
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK
| | - A K Geim
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK
| | - L Eaves
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK. .,School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.
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2
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Elias C, Valvin P, Pelini T, Summerfield A, Mellor CJ, Cheng TS, Eaves L, Foxon CT, Beton PH, Novikov SV, Gil B, Cassabois G. Direct band-gap crossover in epitaxial monolayer boron nitride. Nat Commun 2019; 10:2639. [PMID: 31201328 PMCID: PMC6572751 DOI: 10.1038/s41467-019-10610-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 05/22/2019] [Indexed: 12/01/2022] Open
Abstract
Hexagonal boron nitride is a large band-gap insulating material which complements the electronic and optical properties of graphene and the transition metal dichalcogenides. However, the intrinsic optical properties of monolayer boron nitride remain largely unexplored. In particular, the theoretically expected crossover to a direct-gap in the limit of the single monolayer is presently not confirmed experimentally. Here, in contrast to the technique of exfoliating few-layer 2D hexagonal boron nitride, we exploit the scalable approach of high-temperature molecular beam epitaxy to grow high-quality monolayer boron nitride on graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1 eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit.
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Affiliation(s)
- C Elias
- Laboratoire Charles Coulomb, UMR5221 CNRS-Université de Montpellier, 34095, Montpellier, France
| | - P Valvin
- Laboratoire Charles Coulomb, UMR5221 CNRS-Université de Montpellier, 34095, Montpellier, France
| | - T Pelini
- Laboratoire Charles Coulomb, UMR5221 CNRS-Université de Montpellier, 34095, Montpellier, France
| | - A Summerfield
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - C J Mellor
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - T S Cheng
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - L Eaves
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - C T Foxon
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - P H Beton
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - S V Novikov
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - B Gil
- Laboratoire Charles Coulomb, UMR5221 CNRS-Université de Montpellier, 34095, Montpellier, France
| | - G Cassabois
- Laboratoire Charles Coulomb, UMR5221 CNRS-Université de Montpellier, 34095, Montpellier, France.
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3
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Krishna Kumar R, Chen X, Auton GH, Mishchenko A, Bandurin DA, Morozov SV, Cao Y, Khestanova E, Ben Shalom M, Kretinin AV, Novoselov KS, Eaves L, Grigorieva IV, Ponomarenko LA, Fal'ko VI, Geim AK. High-temperature quantum oscillations caused by recurring Bloch states in graphene superlattices. Science 2018; 357:181-184. [PMID: 28706067 DOI: 10.1126/science.aal3357] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Accepted: 06/09/2017] [Indexed: 11/03/2022]
Abstract
Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties. Cryogenic temperatures are usually required to observe these oscillations. We show that graphene superlattices support a different type of quantum oscillation that does not rely on Landau quantization. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few tesla. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell. Our work hints at unexplored physics in Hofstadter butterfly systems at high temperatures.
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Affiliation(s)
- R Krishna Kumar
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.,Department of Physics, University of Lancaster, Lancaster LA1 4YW, UK
| | - X Chen
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - G H Auton
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A Mishchenko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - D A Bandurin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - S V Morozov
- Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka 142432, Russia.,National University of Science and Technology (MISiS), Moscow 119049, Russia
| | - Y Cao
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - E Khestanova
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - M Ben Shalom
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - A V Kretinin
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.,School of Materials, University of Manchester, Manchester M13 9PL, UK
| | - K S Novoselov
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - L Eaves
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.,School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - I V Grigorieva
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - L A Ponomarenko
- Department of Physics, University of Lancaster, Lancaster LA1 4YW, UK
| | - V I Fal'ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK. .,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A K Geim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK. .,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
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4
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Kudrynskyi ZR, Bhuiyan MA, Makarovsky O, Greener JDG, Vdovin EE, Kovalyuk ZD, Cao Y, Mishchenko A, Novoselov KS, Beton PH, Eaves L, Patanè A. Giant Quantum Hall Plateau in Graphene Coupled to an InSe van der Waals Crystal. Phys Rev Lett 2017; 119:157701. [PMID: 29077458 DOI: 10.1103/physrevlett.119.157701] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Indexed: 05/07/2023]
Abstract
We report on a "giant" quantum Hall effect plateau in a graphene-based field-effect transistor where graphene is capped by a layer of the van der Waals crystal InSe. The giant quantum Hall effect plateau arises from the close alignment of the conduction band edge of InSe with the Dirac point of graphene. This feature enables the magnetic-field- and electric-field-effect-induced transfer of charge carriers between InSe and the degenerate Landau level states of the adjacent graphene layer, which is coupled by a van der Waals heterointerface to the InSe.
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Affiliation(s)
- Z R Kudrynskyi
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - M A Bhuiyan
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - O Makarovsky
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - J D G Greener
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - E E Vdovin
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
- Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka 142432, Russia
| | - Z D Kovalyuk
- Institute for Problems of Materials Science, The National Academy of Sciences of Ukraine, Chernivtsi Branch, Chernivtsi 58001, Ukraine
| | - Y Cao
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - A Mishchenko
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - K S Novoselov
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - P H Beton
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - L Eaves
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - A Patanè
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
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5
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Albar JD, Summerfield A, Cheng TS, Davies A, Smith EF, Khlobystov AN, Mellor CJ, Taniguchi T, Watanabe K, Foxon CT, Eaves L, Beton PH, Novikov SV. An atomic carbon source for high temperature molecular beam epitaxy of graphene. Sci Rep 2017; 7:6598. [PMID: 28747805 PMCID: PMC5529545 DOI: 10.1038/s41598-017-07021-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 06/20/2017] [Indexed: 12/04/2022] Open
Abstract
We report the use of a novel atomic carbon source for the molecular beam epitaxy (MBE) of graphene layers on hBN flakes and on sapphire wafers at substrate growth temperatures of ~1400 °C. The source produces a flux of predominantly atomic carbon, which diffuses through the walls of a Joule-heated tantalum tube filled with graphite powder. We demonstrate deposition of carbon on sapphire with carbon deposition rates up to 12 nm/h. Atomic force microscopy measurements reveal the formation of hexagonal moiré patterns when graphene monolayers are grown on hBN flakes. The Raman spectra of the graphene layers grown on hBN and sapphire with the sublimation carbon source and the atomic carbon source are similar, whilst the nature of the carbon aggregates is different - graphitic with the sublimation carbon source and amorphous with the atomic carbon source. At MBE growth temperatures we observe etching of the sapphire wafer surface by the flux from the atomic carbon source, which we have not observed in the MBE growth of graphene with the sublimation carbon source.
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Affiliation(s)
- J D Albar
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - A Summerfield
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - T S Cheng
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - A Davies
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.,Nanoscale and microscale research centre (NMRC) and School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK
| | - E F Smith
- Nanoscale and microscale research centre (NMRC) and School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK
| | - A N Khlobystov
- Nanoscale and microscale research centre (NMRC) and School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK
| | - C J Mellor
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - T Taniguchi
- The National Institute for Materials Science, Advanced Materials Laboratory, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
| | - K Watanabe
- The National Institute for Materials Science, Advanced Materials Laboratory, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
| | - C T Foxon
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - L Eaves
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - P H Beton
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
| | - S V Novikov
- School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
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6
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Di Paola DM, Kesaria M, Makarovsky O, Velichko A, Eaves L, Mori N, Krier A, Patanè A. Resonant Zener tunnelling via zero-dimensional states in a narrow gap diode. Sci Rep 2016; 6:32039. [PMID: 27535896 PMCID: PMC4989182 DOI: 10.1038/srep32039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Accepted: 07/26/2016] [Indexed: 11/09/2022] Open
Abstract
Interband tunnelling of carriers through a forbidden energy gap, known as Zener tunnelling, is a phenomenon of fundamental and technological interest. Its experimental observation in the Esaki p-n semiconductor diode has led to the first demonstration and exploitation of quantum tunnelling in a condensed matter system. Here we demonstrate a new type of Zener tunnelling that involves the resonant transmission of electrons through zero-dimensional (0D) states. In our devices, a narrow quantum well of the mid-infrared (MIR) alloy In(AsN) is placed in the intrinsic (i) layer of a p-i-n diode. The incorporation of nitrogen in the quantum well creates 0D states that are localized on nanometer lengthscales. These levels provide intermediate states that act as "stepping stones" for electrons tunnelling across the diode and give rise to a negative differential resistance (NDR) that is weakly dependent on temperature. These electron transport properties have potential for the development of nanometre-scale non-linear components for electronics and MIR photonics.
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Affiliation(s)
- D M Di Paola
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, UK
| | - M Kesaria
- Physics Department, Lancaster University, Lancaster LA1 4YB, UK
| | - O Makarovsky
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, UK
| | - A Velichko
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, UK
| | - L Eaves
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, UK
| | - N Mori
- Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita City, Osaka 565-0871, Japan
| | - A Krier
- Physics Department, Lancaster University, Lancaster LA1 4YB, UK
| | - A Patanè
- School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD, UK
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7
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Wallbank JR, Ghazaryan D, Misra A, Cao Y, Tu JS, Piot BA, Potemski M, Pezzini S, Wiedmann S, Zeitler U, Lane TLM, Morozov SV, Greenaway MT, Eaves L, Geim AK, Fal'ko VI, Novoselov KS, Mishchenko A. Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures. Science 2016; 353:575-9. [DOI: 10.1126/science.aaf4621] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 07/13/2016] [Indexed: 11/02/2022]
Affiliation(s)
- J. R. Wallbank
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - D. Ghazaryan
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - A. Misra
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - Y. Cao
- Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - J. S. Tu
- Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - B. A. Piot
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - M. Potemski
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - S. Pezzini
- High Field Magnet Laboratory (HFML-EMFL) and Institute of Molecules and Materials, Radboud University, Nijmegen, 6525 ED, Netherlands
| | - S. Wiedmann
- High Field Magnet Laboratory (HFML-EMFL) and Institute of Molecules and Materials, Radboud University, Nijmegen, 6525 ED, Netherlands
| | - U. Zeitler
- High Field Magnet Laboratory (HFML-EMFL) and Institute of Molecules and Materials, Radboud University, Nijmegen, 6525 ED, Netherlands
| | - T. L. M. Lane
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - S. V. Morozov
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka 142432, Russia
- National University of Science and Technology “MISiS”, 119049, Leninsky pr. 4, Moscow, Russia
| | - M. T. Greenaway
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - L. Eaves
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - A. K. Geim
- Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - V. I. Fal'ko
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - K. S. Novoselov
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - A. Mishchenko
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
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8
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Vdovin EE, Mishchenko A, Greenaway MT, Zhu MJ, Ghazaryan D, Misra A, Cao Y, Morozov SV, Makarovsky O, Fromhold TM, Patanè A, Slotman GJ, Katsnelson MI, Geim AK, Novoselov KS, Eaves L. Phonon-Assisted Resonant Tunneling of Electrons in Graphene-Boron Nitride Transistors. Phys Rev Lett 2016; 116:186603. [PMID: 27203338 DOI: 10.1103/physrevlett.116.186603] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Indexed: 05/07/2023]
Abstract
We observe a series of sharp resonant features in the differential conductance of graphene-hexagonal boron nitride-graphene tunnel transistors over a wide range of bias voltages between 10 and 200 mV. We attribute them to electron tunneling assisted by the emission of phonons of well-defined energy. The bias voltages at which they occur are insensitive to the applied gate voltage and hence independent of the carrier densities in the graphene electrodes, so plasmonic effects can be ruled out. The phonon energies corresponding to the resonances are compared with the lattice dispersion curves of graphene-boron nitride heterostructures and are close to peaks in the single phonon density of states.
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Affiliation(s)
- E E Vdovin
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
- Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka 142432, Russia
- National University of Science and Technology "MISiS," 119049 Leninsky Prospect 4, Moscow, Russia
| | - A Mishchenko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - M T Greenaway
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - M J Zhu
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - D Ghazaryan
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - A Misra
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Y Cao
- Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, United Kingdom
| | - S V Morozov
- Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka 142432, Russia
- National University of Science and Technology "MISiS," 119049 Leninsky Prospect 4, Moscow, Russia
| | - O Makarovsky
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - T M Fromhold
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - A Patanè
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - G J Slotman
- Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - M I Katsnelson
- Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - A K Geim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
- Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, United Kingdom
| | - K S Novoselov
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - L Eaves
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
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9
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Mishchenko A, Tu JS, Cao Y, Gorbachev RV, Wallbank JR, Greenaway MT, Morozov VE, Morozov SV, Zhu MJ, Wong SL, Withers F, Woods CR, Kim YJ, Watanabe K, Taniguchi T, Vdovin EE, Makarovsky O, Fromhold TM, Fal'ko VI, Geim AK, Eaves L, Novoselov KS. Twist-controlled resonant tunnelling in graphene/boron nitride/graphene heterostructures. Nat Nanotechnol 2014; 9:808-813. [PMID: 25194946 DOI: 10.1038/nnano.2014.187] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 08/05/2014] [Indexed: 05/28/2023]
Abstract
Recent developments in the technology of van der Waals heterostructures made from two-dimensional atomic crystals have already led to the observation of new physical phenomena, such as the metal-insulator transition and Coulomb drag, and to the realization of functional devices, such as tunnel diodes, tunnel transistors and photovoltaic sensors. An unprecedented degree of control of the electronic properties is available not only by means of the selection of materials in the stack, but also through the additional fine-tuning achievable by adjusting the built-in strain and relative orientation of the component layers. Here we demonstrate how careful alignment of the crystallographic orientation of two graphene electrodes separated by a layer of hexagonal boron nitride in a transistor device can achieve resonant tunnelling with conservation of electron energy, momentum and, potentially, chirality. We show how the resonance peak and negative differential conductance in the device characteristics induce a tunable radiofrequency oscillatory current that has potential for future high-frequency technology.
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Affiliation(s)
- A Mishchenko
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J S Tu
- Centre for Mesoscience &Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - Y Cao
- Centre for Mesoscience &Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - R V Gorbachev
- Centre for Mesoscience &Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - J R Wallbank
- Physics Department, Lancaster University, Lancaster University LA1 4YB, UK
| | - M T Greenaway
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - V E Morozov
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - S V Morozov
- Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka 142432, Russia
| | - M J Zhu
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - S L Wong
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - F Withers
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - C R Woods
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Y-J Kim
- 1] Centre for Mesoscience &Nanotechnology, University of Manchester, Manchester M13 9PL, UK [2] Department of Chemistry, Seoul National University, Seoul 151-747, Korea
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - E E Vdovin
- 1] School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK [2] Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka 142432, Russia
| | - O Makarovsky
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - T M Fromhold
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - V I Fal'ko
- Physics Department, Lancaster University, Lancaster University LA1 4YB, UK
| | - A K Geim
- 1] School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK [2] Centre for Mesoscience &Nanotechnology, University of Manchester, Manchester M13 9PL, UK
| | - L Eaves
- 1] School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK [2] School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - K S Novoselov
- School of Physics &Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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10
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Young ESK, Akimov AV, Henini M, Eaves L, Kent AJ. Subterahertz acoustical pumping of electronic charge in a resonant tunneling device. Phys Rev Lett 2012; 108:226601. [PMID: 23003634 DOI: 10.1103/physrevlett.108.226601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Indexed: 05/07/2023]
Abstract
We demonstrate that controlled subnanosecond bursts of electronic charge can be transferred through a resonant tunneling diode by successive picosecond acoustic pulses. The effect exploits the nonlinear current-voltage characteristics of the device and its asymmetric response to the compressive and tensile components of the strain pulse. This acoustoelectronic pump opens new possibilities for the control of quantum phenomena in nanostructures.
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Affiliation(s)
- E S K Young
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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11
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Makarovsky O, Vdovin EE, Patané A, Eaves L, Makhonin MN, Tartakovskii AI, Hopkinson M. Laser location and manipulation of a single quantum tunneling channel in an InAs quantum dot. Phys Rev Lett 2012; 108:117402. [PMID: 22540507 DOI: 10.1103/physrevlett.108.117402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Indexed: 05/31/2023]
Abstract
We use a femtowatt focused laser beam to locate and manipulate a single quantum tunneling channel associated with an individual InAs quantum dot within an ensemble of dots. The intensity of the directed laser beam tunes the tunneling current through the targeted dot with an effective optical gain of 10(7) and modifies the curvature of the dot's confining potential and the spatial extent of its ground state electron eigenfunction. These observations are explained by the effect of photocreated hole charges which become bound close to the targeted dot, thus acting as an optically induced gate electrode.
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Affiliation(s)
- O Makarovsky
- School of Physics and Astronomy, The University of Nottingham, United Kingdom
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12
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Britnell L, Gorbachev RV, Jalil R, Belle BD, Schedin F, Mishchenko A, Georgiou T, Katsnelson MI, Eaves L, Morozov SV, Peres NMR, Leist J, Geim AK, Novoselov KS, Ponomarenko LA. Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures. Science 2012; 335:947-50. [PMID: 22300848 DOI: 10.1126/science.1218461] [Citation(s) in RCA: 910] [Impact Index Per Article: 75.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- L Britnell
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
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13
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Hill RJA, Eaves L. Addendum to "Vibrations of a diamagnetically levitated water droplet". Phys Rev E Stat Nonlin Soft Matter Phys 2012; 85:017301. [PMID: 22400708 DOI: 10.1103/physreve.85.017301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Indexed: 05/31/2023]
Abstract
We derive an analytical expression for the frequency of the shape oscillations of a diamagnetically levitated water droplet, in which the equilibrium shape is not spherical. We give the eigenfrequencies of all modes to first order in the oscillation amplitude and potential energy of the magnetogravitational trap confining the droplet. We compare the result with experimental measurements of the eigenfrequencies.
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Affiliation(s)
- R J A Hill
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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14
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Baumgartner A, Stock E, Patanè A, Eaves L, Henini M, Bimberg D. Optical imaging of electrical carrier injection into individual InAs quantum dots. Phys Rev Lett 2010; 105:257401. [PMID: 21231625 DOI: 10.1103/physrevlett.105.257401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Indexed: 05/30/2023]
Abstract
We image the micro-electroluminescence (EL) spectra of self-assembled InAs quantum dots (QDs) embedded in the intrinsic region of a GaAs p-i-n diode and demonstrate optical detection of carrier injection into a single QD. Tunneling of electrons and holes into the QDs at bias voltages below the flat-band condition leads to a spectrum of sharp EL lines from a small number of bright spots on the diode surface, characteristic of emission from individual QDs. We explain this behavior in terms of Coulomb interaction effects and the selective excitation of a small number of QDs within the ensemble due to preferential tunneling paths for carriers.
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Affiliation(s)
- A Baumgartner
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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15
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Wijnheijmer AP, Makarovsky O, Garleff JK, Eaves L, Campion RP, Gallagher BL, Koenraad PM. Nanoscale potential fluctuations in (GaMn)As/GaAs heterostructures: from individual ions to charge clusters and electrostatic quantum dots. Nano Lett 2010; 10:4874-4879. [PMID: 21038865 DOI: 10.1021/nl102739y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
During growth of the dilute p-type ferromagnetic semiconductor Ga1-xMnxAs, interstitial manganese, Mni(2+), is formed when x exceeds 2%. The double donor Mni(2+) compensates the free holes that mediate ferromagnetism. Annealing causes out-diffusion of these interstitials, thereby increasing the Curie temperature. Here, we use cross sectional scanning tunneling microscopy and spectroscopy to visualize the potential landscape which arises due to the clustering of Mni(2+) in annealed p-i-n (GaMn)As-GaAs double barrier heterostructures. We map the local minima in the potential landscape, link them to clusters of individual Mni(2+) ions, and show that the ions are doubly charged.
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Affiliation(s)
- A P Wijnheijmer
- COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands
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16
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Patanè A, Mori N, Makarovsky O, Eaves L, Zambrano ML, Arce JC, Dickinson L, Maude DK. Manipulating and imaging the shape of an electronic wave function by magnetotunneling spectroscopy. Phys Rev Lett 2010; 105:236804. [PMID: 21231494 DOI: 10.1103/physrevlett.105.236804] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Indexed: 05/30/2023]
Abstract
We measure the current due to electrons tunneling through the ground state of hydrogenic Si donors placed in a GaAs quantum well in the presence of a magnetic field tilted at an angle to the plane of the well. The component of B parallel to the direction of current compresses the donor wave function. By measuring the current as a function of the perpendicular component of B, we probe how the magnetocompression affects the spatial form of the wave function and observe directly the transition from Coulombic to magnetic confinement at high fields.
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Affiliation(s)
- A Patanè
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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17
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Mašek J, Máca F, Kudrnovský J, Makarovsky O, Eaves L, Campion RP, Edmonds KW, Rushforth AW, Foxon CT, Gallagher BL, Novák V, Sinova J, Jungwirth T. Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As. Phys Rev Lett 2010; 105:227202. [PMID: 21231418 DOI: 10.1103/physrevlett.105.227202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Indexed: 05/30/2023]
Abstract
We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parametrization and the full potential local-density approximation+U calculations give a very similar band structure whose microscopic spectral character is consistent with the physical premise of the k·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range, we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As.
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Affiliation(s)
- J Mašek
- Institute of Physics ASCR, v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic
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18
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Hill RJA, Eaves L. Vibrations of a diamagnetically levitated water droplet. Phys Rev E Stat Nonlin Soft Matter Phys 2010; 81:056312. [PMID: 20866327 DOI: 10.1103/physreve.81.056312] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Revised: 04/14/2010] [Indexed: 05/29/2023]
Abstract
We measure the frequencies of small-amplitude shape oscillations of a magnetically levitated water droplet. The droplet levitates in a magnetogravitational potential trap. The restoring forces of the trap, acting on the droplet's surface in addition to the surface tension, increase the frequency of the oscillations. We derive the eigenfrequencies of the normal mode vibrations of a spherical droplet in the trap and compare them with our experimental measurements. We also consider the effect of the shape of the potential trap on the eigenfrequencies.
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Affiliation(s)
- R J A Hill
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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19
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Patanè A, Allison G, Eaves L, Hopkinson M, Hill G, Ignatov A. Tailoring the electrical conductivity of GaAs by nitrogen incorporation. J Phys Condens Matter 2009; 21:174209. [PMID: 21825413 DOI: 10.1088/0953-8984/21/17/174209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We investigate the electrical conductivity of the dilute nitride alloy GaAs(1-x)N(x), focusing on the range of concentrations of N over which this material system behaves as a good conductor. We report a large increase of the resistivity for x>0.2% and a strong reduction of the electron mobility, μ, at x∼0.1%. In the ultra-dilute regime (x∼0.1%) and at low electric fields (<1 kV cm(-1)), the electrical conductivity retains the characteristic features of electron transport through extended states, albeit with relatively low mobility (μ∼0.1 m(2) V(-1) s(-1) at T = 293 K) due to scattering of electrons by N atoms. In contrast, at large electric fields (>1 kV cm(-1)), the conduction electrons gain sufficient energy to approach the energy of the resonant N level, where they become spatially localized. This resonant electron localization in an electric field (RELIEF) leads to negative differential velocity. The RELIEF effect could be observed in other III-N-V compounds, such as InAs(1-x)N(x) and InP(1-x)N(x), and has potential for applications in terahertz electronics.
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Affiliation(s)
- A Patanè
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
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20
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Abstract
The shape of a weightless spinning liquid droplet is governed by the balance between the surface tension and centrifugal forces. The axisymmetric shape for slow rotation becomes unstable to a nonaxisymmetric distortion above a critical angular velocity, beyond which the droplet progresses through a series of 2-lobed shapes. Theory predicts the existence of a family of 3- and 4-lobed equilibrium shapes at higher angular velocity. We investigate the formation of a triangular-shaped magnetically levitated water droplet, driven to rotate by the Lorentz force on an ionic current within the droplet. We also study equatorial traveling waves which give the droplet threefold, fourfold, and fivefold symmetry.
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Affiliation(s)
- R J A Hill
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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21
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Makarovsky O, Thomas O, Balanov AG, Eaves L, Patanè A, Campion RP, Foxon CT, Vdovin EE, Maude DK, Kiesslich G, Airey RJ. Fock-Darwin-like quantum dot states formed by charged Mn interstitial ions. Phys Rev Lett 2008; 101:226807. [PMID: 19113508 DOI: 10.1103/physrevlett.101.226807] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Indexed: 05/27/2023]
Abstract
We report a method of creating electrostatically induced quantum dots by thermal diffusion of interstitial Mn ions out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This approach creates deep, approximately circular, and strongly confined dotlike potential minima in a large (200 microm) mesa diode structure without need for advanced lithography or electrostatic gating. Magnetotunneling spectroscopy of an individual dot reveals the symmetry of its electronic eigenfunctions and a rich energy level spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| from 0 to 11.
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Affiliation(s)
- O Makarovsky
- School of Physics & Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
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22
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Balanov AG, Fowler D, Patanè A, Eaves L, Fromhold TM. Bifurcations and chaos in semiconductor superlattices with a tilted magnetic field. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:026209. [PMID: 18352105 DOI: 10.1103/physreve.77.026209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Revised: 10/30/2007] [Indexed: 05/26/2023]
Abstract
We study the effects of dissipation on electron transport in a semiconductor superlattice with an applied bias voltage and a magnetic field that is tilted relative to the superlattice axis. In previous work, we showed that, although the applied fields are stationary, they act like a terahertz plane wave, which strongly couples the Bloch and cyclotron motion of electrons within the lowest miniband. As a consequence, the electrons exhibit a unique type of Hamiltonian chaos, which creates an intricate mesh of conduction channels (a stochastic web) in phase space, leading to a large resonant increase in the current flow at critical values of the applied voltage. This phase-space patterning provides a sensitive mechanism for controlling electrical resistance. In this paper, we investigate the effects of dissipation on the electron dynamics by modifying the semiclassical equations of motion to include a linear damping term. We demonstrate that, even in the presence of dissipation, deterministic chaos plays an important role in the electron transport process. We identify mechanisms for the onset of chaos and explore the associated sequence of bifurcations in the electron trajectories. When the Bloch and cyclotron frequencies are commensurate, complex multistability phenomena occur in the system. In particular, for fixed values of the control parameters several distinct stable regimes can coexist, each corresponding to different initial conditions. We show that this multistability has clear, experimentally observable, signatures in the electron transport characteristics.
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Affiliation(s)
- A G Balanov
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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23
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Silberg J, Meyer J, Pickles A, Simonoff E, Eaves L, Hewitt J, Maes H, Rutter M. Heterogeneity among juvenile antisocial behaviours: findings from the Virginia Twin Study of Adolescent Behavioural Development. Ciba Found Symp 2007; 194:76-86; discussion 86-92. [PMID: 8862871 DOI: 10.1002/9780470514825.ch5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The examination of heterogeneity in antisocial behaviour was accomplished by applying latent class analytic methods to multivariate categorical data on 389 same-sex male twins, aged 11 to 16 from the Virginia Twin Study of Adolescent Behavioural Development (VTSABD). The data included multiple measures of oppositional and conduct disorder, attention deficit disorder, hyperactivity, impulsivity, reading disability and anxiety from mother, teacher, and child report from both questionnaire and interview (child and adult psychiatric assessment; CAPA). A latent four-class model provided a good fit to the data and yielded four phenotypically and aetiologically distinct latent classes: (1) a non-symptomatic class influenced by both additive genetic and shared environmental factors; (2) a hyperactivity-conduct disturbance class accounted for by both additive and non-additive genetic effects; (3) a 'pure' conduct disturbance class with a very strong shared environmental component; and (4) a multisymptomatic class explained entirely by the additive effect of the genes. Further characterization of these four latent classes by age of the child and parental psychiatric history is also shown.
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Affiliation(s)
- J Silberg
- Department of Human Genetics, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA
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24
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Allison G, Mori N, Patanè A, Endicott J, Eaves L, Maude DK, Hopkinson M. Strong effect of resonant impurities on Landau-level quantization. Phys Rev Lett 2006; 96:236802. [PMID: 16803389 DOI: 10.1103/physrevlett.96.236802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Indexed: 05/10/2023]
Abstract
We investigate experimentally the effect of a random distribution of nitrogen (N) impurities on the Landau-level spectrum of a GaAs quantum well. Our magnetotunneling study reveals complex and nonequally spaced Landau levels and a quenching of the Landau states at a well-defined bias and electron energy which is resonant with that of the N atoms. Analysis of the magnetic field dependence of the tunnel current into the Landau levels of the well also provides quantitative information about the nonresonant component of the N-related scattering potential.
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Affiliation(s)
- G Allison
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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25
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Patanè A, Mori N, Fowler D, Eaves L, Henini M, Maude DK, Hamaguchi C, Airey R. Magnetic-field-induced suppression of electronic conduction in a superlattice. Phys Rev Lett 2004; 93:146801. [PMID: 15524824 DOI: 10.1103/physrevlett.93.146801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2004] [Indexed: 05/24/2023]
Abstract
We use a magnetic field applied along the axis of a semiconductor superlattice (SL) as a controllable means of creating a one-dimensional band structure. We demonstrate that the current flow through the SL is strongly suppressed when the electron motion perpendicular to the SL axis is strongly confined by the quantizing magnetic field. By modeling this behavior using semiclassical and nonequilibrium Green's function methods, we show that the observed quenching arises from a qualitative change in electron dynamics caused by increasing quantum confinement.
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Affiliation(s)
- A Patanè
- School of Physics and Astronomy, University of Nottingham, NG7 2RD, United Kingdom.
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26
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Fromhold TM, Patanè A, Bujkiewicz S, Wilkinson PB, Fowler D, Sherwood D, Stapleton SP, Krokhin AA, Eaves L, Henini M, Sankeshwar NS, Sheard FW. Chaotic electron diffusion through stochastic webs enhances current flow in superlattices. Nature 2004; 428:726-30. [PMID: 15085125 DOI: 10.1038/nature02445] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2003] [Accepted: 02/27/2004] [Indexed: 11/09/2022]
Abstract
Understanding how complex systems respond to change is of fundamental importance in the natural sciences. There is particular interest in systems whose classical newtonian motion becomes chaotic as an applied perturbation grows. The transition to chaos usually occurs by the gradual destruction of stable orbits in parameter space, in accordance with the Kolmogorov-Arnold-Moser (KAM) theorem--a cornerstone of nonlinear dynamics that explains, for example, gaps in the asteroid belt. By contrast, 'non-KAM' chaos switches on and off abruptly at critical values of the perturbation frequency. This type of dynamics has wide-ranging implications in the theory of plasma physics, tokamak fusion, turbulence, ion traps, and quasicrystals. Here we realize non-KAM chaos experimentally by exploiting the quantum properties of electrons in the periodic potential of a semiconductor superlattice with an applied voltage and magnetic field. The onset of chaos at discrete voltages is observed as a large increase in the current flow due to the creation of unbound electron orbits, which propagate through intricate web patterns in phase space. Non-KAM chaos therefore provides a mechanism for controlling the electrical conductivity of a condensed matter device: its extreme sensitivity could find applications in quantum electronics and photonics.
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Affiliation(s)
- T M Fromhold
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK.
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27
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Foxon CT, Novikov SV, Belyaev AE, Zhao LX, Makarovsky O, Walker DJ, Eaves L, Dykeman RI, Danylyuk SV, Vitusevich SA, Kappers MJ, Barnard JS, Humphreys CJ. Current–voltage instabilities in GaN/AlGaN resonant tunnelling structures. ACTA ACUST UNITED AC 2003. [DOI: 10.1002/pssc.200303376] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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28
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Endicott J, Patanè A, Ibáñez J, Eaves L, Bissiri M, Hopkinson M, Airey R, Hill G. Magnetotunneling spectroscopy of dilute Ga(AsN) quantum wells. Phys Rev Lett 2003; 91:126802. [PMID: 14525385 DOI: 10.1103/physrevlett.91.126802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2003] [Indexed: 05/24/2023]
Abstract
We use magnetotunneling spectroscopy to explore the admixing of the extended GaAs conduction band states with the localized N-impurity states in dilute GaAs(1-y)N(y) quantum wells. In our resonant tunneling diodes, electrons can tunnel into the N-induced E- and E+ subbands in a GaAs(1-y)N(y) quantum well layer, leading to resonant peaks in the current-voltage characteristics. By varying the magnetic field applied perpendicular to the current direction, we can tune an electron to tunnel into a given k state of the well; since the applied voltage tunes the energy, we can map out the form of the energy-momentum dispersion curves of E- and E+. The data reveal that for a small N content (approximately 0.1%) the E- and E+ subbands are highly nonparabolic and that the heavy effective mass E+ states have a significant Gamma-conduction band character even at k=0.
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Affiliation(s)
- J Endicott
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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29
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Martin AM, Benedict KA, Sheard FW, Eaves L. Model for the voltage steps in the breakdown of the integer quantum Hall effect. Phys Rev Lett 2003; 91:126803. [PMID: 14525386 DOI: 10.1103/physrevlett.91.126803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2002] [Revised: 03/12/2003] [Indexed: 05/24/2023]
Abstract
In samples used to maintain the U.S. resistance standard the breakdown of the dissipationless integer quantum Hall effect occurs as a series of dissipative voltage steps. A mechanism for this type of breakdown is proposed, based on the generation of magnetoexcitons when the quantum Hall fluid flows past an ionized impurity above a critical velocity. The calculated generation rate gives a voltage step height in good agreement with measurements on both electron and hole gases. We also compare this model to a hydrodynamic description of breakdown.
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Affiliation(s)
- A M Martin
- School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, United Kingdom
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30
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Catherall AT, Benedict KA, King PJ, Eaves L. Surface instabilities on liquid oxygen in an inhomogeneous magnetic field. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 68:037302. [PMID: 14524930 DOI: 10.1103/physreve.68.037302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2003] [Indexed: 05/24/2023]
Abstract
Liquid oxygen exhibits surface instabilities when subjected to a sufficiently strong magnetic field. A vertically oriented magnetic field gradient both increases the magnetic field value at which the pattern forms and shrinks the length scale of the surface patterning. We show that these effects of the field gradient may be described in terms of an "effective gravity," which in our experiments may be varied from 1 g to 360 g.
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Affiliation(s)
- A T Catherall
- School of Physics and Astronomy, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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31
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Affiliation(s)
- A T Catherall
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
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32
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Abstract
BACKGROUND There is huge individual variation in people's response to negative life events. AIMS To test the hypothesis that genetic factors moderate susceptibility to the environmentally mediated risks associated with negative life events. METHOD The Virginia Twin Study of Adolescent Behavioral Development (VTSABD) was used to study the effects of independent life events (assessed from maternal interview) on depression/anxiety (assessed from child interview) in 184 same-gender female twin pairs, aged 14--7 years, measured on two occasions. RESULTS There was no genetic effect on the independent negative life events studied. A significant gene-environment interaction was found using structural equation modelling. There was no effect of independent life events on adolescents' depression in the absence of parental emotional disorder, but a significant effect in its presence. CONCLUSIONS There is an environmentally mediated effect of life events on depression/anxiety. Genetic factors play a significant role in individual differences in susceptibility to these environmentally mediated risks.
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Affiliation(s)
- J Silberg
- Department of Human Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia 23298-0030, USA.
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Fromhold TM, Krokhin AA, Tench CR, Bujkiewicz S, Wilkinson PB, Sheard FW, Eaves L. Effects of stochastic webs on chaotic electron transport in semiconductor superlattices. Phys Rev Lett 2001; 87:046803. [PMID: 11461635 DOI: 10.1103/physrevlett.87.046803] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2000] [Indexed: 05/23/2023]
Abstract
We investigate chaotic electron transport in the lowest miniband of a semiconductor superlattice with a tilted magnetic field. This experimentally accessible non-Kolmogorov-Arnol'd-Moser system involves only stationary electric and magnetic fields, but is dynamically equivalent to a time-dependent kicked harmonic oscillator. The onset of chaos strongly delocalizes the electron orbits, thus raising the electrical conductivity. When the cyclotron and Bloch frequencies are commensurate, the phase space is threaded by a stochastic web, which produces a further resonant increase in the conductivity.
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Affiliation(s)
- T M Fromhold
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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Abstract
BACKGROUND The purpose of the present study was to investigate the role of genetic and environmental factors in the association between depressive symptoms and symptoms of overanxious disorder, simple phobias, and separation anxiety in 8-13-year-old and 14-17-year-old girls. METHODS Multivariate genetic models were fitted to child-reported longitudinal symptom data gathered from clinical interview on 415 MZ [corrected] and 194 DZ [corrected] female twin pairs from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) [corrected]. RESULTS Model-fitting results suggest there are distinct etiological [corrected] patterns underlying the association between depression and the different anxiety syndromes during the course of development: 1) specific genetic influences on depression after age 14 reflect liability to symptoms of earlier overanxious disorder (OAD) and simple phobias; 2) aspects of the shared environment that influence symptoms of depression before age 14 contribute to symptoms of separation anxiety and simple phobias later in adolescence [corrected]; 3) the shared environmental influence on [corrected] depression in 14+ girls also affects liability to symptoms of concurrent OAD and persistent separation anxiety. CONCLUSIONS These results suggest that depression before and after age 14 may be etiologically distinct syndromes. Earlier symptoms of OAD and (to a lesser extent phobic symptoms) [corrected] reflect the same genetic risk, and separation anxiety symptoms both before and after age 14 reflect the same environmental risk that influence liability to depressive symptoms expressed in middle to late adolescence.
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Affiliation(s)
- J L Silberg
- Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia 23298-0003, USA
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Abstract
There have been strong critiques of the notion that environmental influences can have an important effect on psychological functioning. The substance of these criticisms is considered in order to infer the methodological challenges that have to be met. Concepts of cause and of the testing of causal effects are discussed with a particular focus on the need to consider sample selection and the value (and limitations) of longitudinal data. The designs that may be used to test hypotheses on specific environmental risk mechanisms for psychopathology are discussed in relation to a range of adoption strategies, twin designs, various types of "natural experiments," migration designs, the study of secular change, and intervention designs. In each case, consideration is given to the need for samples that "pull-apart" variables that ordinarily go together, specific hypotheses on possible causal processes, and the specification and testing of key assumptions. It is concluded that environmental risk hypotheses can be (and have been) put to the test but that it is usually necessary to use a combination of research strategies.
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Affiliation(s)
- M Rutter
- Social, Genetic and Developmental Psychiatry Research Centre, London, England.
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Eaves L, Stradling RA, Carrere G, Askenazy S, Leotin J, Portal JC, Ulmet JP. An investigation of the conduction band edge in CdSe by the magnetophonon effect. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/5/3/002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Eaves L, Stradling RA, Askenazy S, Leotin J, Portal JC, Ulmet JP. The magnetophonon effect in epitaxial films of n-type inp. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/4/2/018] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Bajaj KK, Birch JR, Eaves L, Hoult RA, Kirkman RF, Simmonds PE, Stradling RA. Spectroscopic evidence for the interaction between shallow hydrogenic donors in GaAs, InP and CdTe. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/8/4/021] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Eaves L, Hoult RA, Stradling RA, Tidey RJ, Portal JC, Askenazy S. Fourier analysis of magnetophonon and two-dimensional Shubnikov-de Haas magnetoresistance structure. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/8/7/019] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Eaves L, Hoult RA, Stradling RA, Askenazy S, Barbaste R, Carrere G, Leotin J, Portal JC, Ulmet P. An investigation of the valence bands of germanium, InSb and GaAs by means of the magnetophonon effect. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/10/15/018] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Eaves L, Williams PJ. Decay of the deep-level extrinsic photoconductivity response of n-GaAs(Cr,Si) at liquid-helium temperature. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/12/18/005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Dunn-Geier J, Ho HH, Auersperg E, Doyle D, Eaves L, Matsuba C, Orrbine E, Pham B, Whiting S. Effect of secretin on children with autism: a randomized controlled trial. Dev Med Child Neurol 2000; 42:796-802. [PMID: 11132252 DOI: 10.1017/s0012162200001481] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
To determine the effect of intravenous porcine secretin on autistic behaviours in children aged 2 to 7 years, the effects of secretin on (1) performance on a standardized language measure, and (2) autistic behaviours, as rated by parents and child development professionals was examined. Employing a randomized, double-blind, placebo-controlled design, 95 participants were assigned to one of two groups and administered a single dose of either secretin or placebo. A follow-up assessment was conducted 3 weeks after the injection. No significant differences in language or autistic behaviour measures were observed at the 3-week follow-up between the groups. Also, there was no significant difference in the proportion of individuals who improved by > or = 6 points on the language measure at follow-up. This study showed no significant effects of secretin on children with autism. Our results are consistent with a systematic review of randomized controlled trials evaluating the effect of secretin in children with autism.
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Affiliation(s)
- J Dunn-Geier
- Child Development Service, Children's Hospital of Eastern Ontario, Ottawa, Canada.
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Duncan KR, Eaves L, Ramdane A, Roys WB, Skolnick MS, Dean PJ. An investigation of the 1.36 eV photoluminescence spectrum of heat-treated InP using Zeeman spectroscopy and strain effects. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/7/016] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Williams PJ, Eaves L, Simmonds PE, Henry MO, Lightowlers EC, Uihlein C. High-resolution optical absorption spectroscopy on Cr-related defects in GaAs and GaP. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/6/026] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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47
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Eaves L, Halliday DP. A model for some defect-related bound exciton lines in the photoluminescence spectrum of GaAs layers grown by molecular beam epitaxy. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/27/003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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48
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Eaves L, Halliday DP, Uihlein C. Interpretation of the 1.03 eV photoluminescence and absorption in GaP(Cr) in terms of internal transitions of Cr3+. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/18/16/002] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Vdovin EE, Levin A, Patanè A, Eaves L, Main PC, Khanin YN, Dubrovskii YV, Henini M, Hill G. Imaging the electron wave function in self-assembled quantum dots. Science 2000; 290:122-4. [PMID: 11021794 DOI: 10.1126/science.290.5489.122] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Magnetotunneling spectroscopy is used as a noninvasive and nondestructive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The technique exploits the effect of the classical Lorentz force on the motion of a tunneling electron and can be regarded as the momentum (k) space analog of scanning tunneling microscopy imaging. The images reveal the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states.
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Affiliation(s)
- E E Vdovin
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
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