1,720,986 research outputs found
Graphene In The Quantum Hall Regime: Effects Of Vacancies, Sublattice Polarization And Disorder
No full textWe investigate the effects of vacancies, disorder and sublattice polarization on the electronic properties of a monolayer graphene in the quantum Hall regime. Energy spectra as a function of magnetic field and the localization properties of the states within the graphene Landau levels (LLs) are calculated through a tight-binding model. We first discuss our results considering vacancies in the lattice, where we show that vacancies introduce extra levels (or well-defined bands) between consecutive LLs. An striking consequence here is that extra Hall resistance plateaus are expected to emerge when an organized vacancy superlattice is considered. Secondly, we discuss the anomalous localization properties we have found for the lowest LL, where an increasing disorder is shown to enhance the wave functions delocalization (instead of inducing localization). This unexpected effect is shown to be directly related to the way disorder increasingly destroys the sublattice (valley) polarization of the states in the lowest LL. The reason why this anomalous disorder effect occurs only for the zero-energy LL is that, in absence of disorder, only for this level all the states are sublattice polarized, i.e., their wave functions have amplitudes in only one of the sublattices. © 2009 World Scientific Publishing Company.23Dez/1326182627Novoselov, K.S., Geim, A.K., Morozov, S.V., Jiang, D., Katsnelson, M.I., Grig-orieva, I.V., Dubonos, S.V., Firsov, A.A., (2005) Nature, 438, p. 197Zhang, Y., Tan, Y.-W., Stormer, H.L., Kim, P., (2005) Nature, 438, p. 201Zhang, Y., Jiang, Z., Small, J.P., Purewal, M.S., Tan, Y.-W., Fazlollahi, M., Chu-dow, J.D., Kim, P., (2006) Phys. Rev. Lett, 96, p. 136806Fuchs, J.N., Lederer, P., (2007) Phys. Rev. Lett, 98, p. 016803Abanin, D.A., Lee, P.A., Levitov, L.S., (2007) Phys. Rev. Lett, 98, p. 156801Koshino, M., Ando, T., (2007) Phys. Rev. B, 75, p. 033412McCann, E., Kechedzhi, K., Fal'ko, V.I., Suzuura, H., Ando, T., Altshuler, B.L., (2006) Phys. Rev. Lett, 97, p. 146805Sheng, L., Sheng, D.N., Haldane, F.D.M., Balents, L., (2007) Phys. Rev. Lett, 99, p. 196802Apalkov, V.M., Chakraborty, T., (2006) Phys. Rev. Lett, 97, p. 126801Rycerz, A., Tworzydlo, J., Beenakker, C.W.J., (2007) Nat. Phys, 3, p. 172Pereira, A.L.C., Schulz, P.A., (2008) Phys. Rev. B, 77, p. 075416Pereira, A.L.C., Schulz, P.A., (2008) Phys. Rev. B, 78, p. 125402Thouless, D.J., Phys (1974) Reports, 13. , 93Pereira, V.M., Guinea, F., Lopes dos Santos, J.M.B., Peres, N.M.R., Castro Neto, A.H., (2006) Phys. Rev. Lett, 96, p. 036801Pereira, V.M., Lopes dos Santos, J.M.B., Castro Neto, A.H., (2008) Phys. Rev. B, 77, p. 115109Palacios, J.J., Fernández-Rossier, J., Brey, L., (2008) Phys. Rev. B, 77, p. 195428N. M. R. Peres, F. Guinea and A. H. Castro Neto, Phys. Rev. B 73, 125411 (2006)Geim, A.K., Novoselov, K.S., (2007) Nat. Mater, 6, p. 183Tapasztó, L., Dobrik, G., Lambin, P., Biró, L.P., (2008) Nature Nanotech, 3, p. 397Giesbers, A.J.M., Zeitlera, U., Neubeck, S., Freitag, F., Novoselov, K.S., Maan, J.C., (2008) Solid State Commun, 147, p. 366Pereira, A.L.C., Schulz, P.A., (2002) Phys. Rev. B, 66, p. 15532
Wave Function Mapping At Fano Resonances And Conductance Switching In Open Quantum Dots
No full textWe numerically simulate the effects of a controllable impurity induced by an atomic microscope tip scanned on an open quantum dot with highly transmitting channels. The coupled quantum dot - tip system may result in a transistor like device, for which the conductance switching is a function of the position, spatial dimensions and potential of the perturbation induced by the tip. For realistic dimensions we show that energy shifts of the resonances deliver a bona fide imaging of low energy isolated quantum dot states, as well as of higher energy states coupled to the continuum (Fano resonances). © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.2831293132Marzin, J.Y., Gerard, J.M., (1989) Phys. Rev. Lett., 62, p. 2172Topinka, M.A., LeRoy, B.J., Shaw, S.E.J., Heller, E.J., Westervelt, R.M., Maranowski, K.D., Gossard, A.C., (2000) Science, 289, p. 2323Lundberg, T., Frost, J.E.F., Berggren, K.F., Ji, Z.L., Liang, C.T., Castleton, I.M., Ritchie, D.A., Pepper, M., (1997) Semicond. Sci. Technol., 12, p. 875Mendoza, M., Schulz, P.A., (2003) Phys. Rev. B, 68, p. 205302Crook, R., Smith, C.G., Graham, A.C., Farrer, I., Beere, H.E., Ritchie, D.A., (2003) Phys. Rev. Lett., 91, p. 246803Datta, S., (2000) Superlattices Microstruc., 28, p. 253M. Mendoza and P. A. Schulz, unpublishedBaranger, H.U., Divicenzo, D.P., Jalabert, R.A., Stone, A.D., (1991) Phys. Rev. B, 44, p. 10637Takagaki, Y., Ploog, K.H., (2004) Phys. Rev. B, 70, p. 07330
Analysis Of The Current-volt Age Characteristics Lineshapes Of Resonant Tunneling Diodes
No full textWe discuss the influence of a two dimensional electron gas at the emitter-barrier interface on the current-voltage characteristics of a GaAs-AlGaAs double-barrier quantum well resonant tunneling diode. This effect is characterized by the modification of the space charge distribution along the structure. Within the framework of a self-consistent calculation we analyse the current-voltage characteristics of the tunneling diodes. This analysis permits us to infer different tunneling ways, related to the formation of confined states in the emitter region, and their signatures in the current-voltage characteristics. We show that varying the spacer layer, together with barrier heights, changes drastically the current density-voltage characteristics lineshapes. We compare our results with a variety of current-voltage characteristics reported in the literature. The general trend of experimental lineshapes can be reproduced and interpreted with our model. The possibility of tunning tunneling paths is predicted for a range that has not yet been explored experimentally.261304307Tsu, R., Esaki, L., (1973) Appl. Phys. Lett., 22, p. 562Chang, L.L., Esaki, L., Tsu, R., (1974) Appl. Phys. Lett., 24, p. 593Sollner, T.C.L., Goodhue, W.D., Tannenwald, P.E., Parker, C.D., Peck, D.D., (1983) Appl. Phys. Lett., 43, p. 588Frensley, W.R., (1987) Phys. Rev. B, 36, p. 1570(1990) Rev. Mod. Phys., 62, p. 745Duke, C.B., Tunneling in Solids (1969) Solid State Physics, (10 SUPPL.). , F. Seitz, D. Turnbull and H. Ehrenreich Eds.Academic Press, New YorkFiig, T., Jauho, A.P., (1991) Appl. Phys. Lett., 59, p. 2245(1992) Surf. Sci., 267, p. 392Sheard, F.W., Toombs, G.A., (1992) Semicond. Sci. Technol., 7, pp. B460Adachi, S., (1985) J. Appl. Phys., 58, pp. R1Rossmanith, M., Syassen, K., Bockenhoff, E., Ploog, K., Von Klitzing, K., (1991) Phys. Rev. B, 44, p. 3168Rivera, P.H., Schulz, P.A., (1995) Appl. Phys. Lett., 67, p. 2675Zaslavsky, A., Goldman, V.J., Tsui, D.C., Cunningham, J.E., (1988) Appl. Phys. Lett., 53, p. 1408Tewordt, M., Martín Moreno, L., Nicholls, J.T., Pepper, M., Kelly, M.J., Law, V.J., Ritchie, D.A., Jones, G.A.C., (1992) Phys. Rev. B, 45, p. 1440
Finite Size Effects On Antidots Array In The Presence Of Magnetic Field
No full textIn this work we discuss the size effects on a small array of antidots under a perpendicular a magnetic field within the framework of a tight-binding model. The coupling of bulk and edge states can be tuned by the magnetic field, as well as by independent eletrostatic modulation of the "bulk" and "surface" of the system. Variation on these parameters raises two types of edge states for the finite lateral superlattice: i) bona fide edge states confined at the surface with tunable coupling to the bulk, and ii) edge states in the internal structure of the bulk self-similar spectra, known as Hofstadter Butterflies.274323326Schlosser, T., Ensslin, K., Kotthaus, J.P., Holland, M., (1996) Europhys. Lett., 33 (9), p. 683Zozulenko, I.V., Maao, F.A., Hauge, E.H., (1995) Phys. Rev., B51, p. 7058Andrade Neto, M.A., Schulz, P.A., (1995) Phys. Rev., B52, p. 14093Hofstadter, D.R., (1976) Phys. Rev., B14, p. 2239Petschel, G., Geisel, T., (1993) Phys. Rev. Lett, 71, p. 239Peierls, R., (1933) Z. Phys., 80, p. 763Ensslin, K., Schuster, R., Schlösser, T., (1995) Proceeding of Nato School, , KievPfannkuche, D., Gerhardts, R.R., (1992) Phys. Rev. B, 46, p. 1260
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
