Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-06T12:19:22Z
No. of bitstreams: 2
license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)
udson cabral.pdf: 2045459 bytes, checksum: 0c5126468995368f097978ee97cb41f5 (MD5) / Made available in DSpace on 2014-08-06T12:19:22Z (GMT). No. of bitstreams: 2
license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)
udson cabral.pdf: 2045459 bytes, checksum: 0c5126468995368f097978ee97cb41f5 (MD5)
Previous issue date: 2010 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We investigate core-shell nanowires of diluted magnetic semiconductors (DMS) with
remote n-type modulation doping. The incorporation of Mn2 ions acting as spin 5/2 impurities
in the core region of the wire gives rise to a strong s-d exchange coupling between electrons
in the wire and those of the d levels of the Mn2 ions. Applying an external magnetic eld
along the axis of the wire, within the mean eld approximation, the s-d exchange generates
a spin-dependent core potential. A gate voltage is applied radially to wire, to obtain some
control over the density of the wire. Electronic strucutre of the wire was calculated within
the e?ective mass approximation, in both approximations Hartree and spin density functional
theory. We calculated the conductance of wire using the Landauer-B?uttiker formulation in the
linear response regime, which generally results in a total conductance with well-de ned plateaus
in GT = 2; 6; 10G0 (G0 = e2=h is the quanta of conductance), which occurred because in the
system investigated the rst level is twofold degenerated (spin degenerescence) and the others
are fourfold degenerated (spin degenerescence and orbital angular momentum). In the absence
of a magnetic eld we observe that when we take into account the e?ects of exchange and
correlation, the states with eigenvalues of Lz nonzero will be polarized while those with l = 0
isn't polarized. This unpolarized level with eigenvalue of Lz null suggests that, perhaps, the
0.7 anomaly (the emergence of two plateau at G = 0:7G0 and the other in G = G0) quantum
wires on existing geometry of split-gate is related to the geometry of the wire. The results for
total energy show that there are a competition between the ferromagnetic and paramagnetic
states. / Investigamos nano fios de semicondutores magnéticos dilu??dos (DMSs - Diluted Magnetic
Semiconductors) do tipo caroço-casca com dopagem remota tipo-n. A incorporação dos
íons de Mn+2, que atuam como impurezas de spin 5/2 no caroço do fi o, faz surgir um forte
acoplamento de trocas dentre os eletrons do fio e aqueles dos níveis d do íon Mn+2. Com a
aplicação de um campo magnético externo ao longo do eixo do fi o, na aproximação de campo
médio, a interação de troca s-d gera um potencial dependente do spin na região do caroço do
fi o. Um potencial de gate é aplicado radialmente ao nanofi o, para obtermos um certo controle
sobre a densidade eletrônica do fi o. Calculamos a estrutura eletrônica do nanofi o de
DMSs usando o modelo da massa efetiva, tanto na aproximação de Hartree quanto na teoria
do funcional da densidade dependente de spin (SDFT - Spin Density Functional Theory).
Calculamos a condutância do nano fio usando a formulação de Landauer-B?uttiker no regime de
resposta linear, o que de modo geral, resultou numa condutância total com platôs bem de finidos
em GT = 2; 6; 10G0 (G0 = e2=h ?e o quanta de condutância), o que ocorreu porque no sistema
investigado a primeira subbanda ?e duplamente degenerada (degenerescência de spin) e as outras
duas são quadruplamente degenerada (degenerescência de spin e de momento angular orbital).
Na ausência de um campo magnético observamos que ao levarmos em conta os efeitos de troca
e correlação, os estados que possuem autovalor de Lz diferente de zero se polarizam enquanto
que os que possuem l = 0 não se polarizam. Essa não-polarização do nível com autovalor de Lz
nulo sugere que, talvez, a anomalia 0,7 (o surgimento de dois platôs um em G = 0; 7G0 e outro
em G = G0) existente em os quânticos com geometria de split-gate esteja relacionada com a
geometria do o. Os resultados obtidos para a energia total mostram que há uma competição
entre os estados ferromagnético e paramagnéticos.
Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.bc.ufg.br:tde/2888 |
Date | January 2010 |
Creators | Mendes, Udson Cabra |
Contributors | Avelar, Ardiley Torres, Leão, Salvino de Araújo |
Publisher | Universidade Federal de Goiás, Programa de Pós-graduação em Fisica (IF), UFG, Brasil, Instituto de Física - IF (RG) |
Source Sets | IBICT Brazilian ETDs |
Language | Portuguese |
Detected Language | English |
Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
Format | application/pdf |
Source | reponame:Biblioteca Digital de Teses e Dissertações da UFG, instname:Universidade Federal de Goiás, instacron:UFG |
Rights | http://creativecommons.org/licenses/by-nc-nd/4.0/, info:eu-repo/semantics/openAccess |
Relation | 3162138865744262028, 600, 600, 600, 600, 600, -4029658853652049306, -8327146296503745929, 2075167498588264571, -2555911436985713659, [1] S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. Von Moln ́ar, M. L. Roukes, A. Y. Chtchelkanova, e D. M. Treger. Spintronics: A Spin-Based Electronics Vision for the Future. Science, 294, 1488, 2001. [2] D. D. Awschalom e M. E. Flatt ́e. Challenges for semiconductor spintronics. Nature Physics, 3, 153–159, 2007. [3] Y. K. Kato, R. C. Myers, A. C. Gossard, e D. D. Awschalom. Observation of the Spin Hall Effect in Semiconductors. Science, 304, 1910, 2004. [4] W. P. McCray. MBE deserves a place in the history books. Nature Nanotechnology, 2, 259, 2007. [5] T. Dieti, D. D. Awschalom, M. Kaminska, e H. Ohno. Spintronics and Semimetals. Elsevier, 2008. [6] M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, e J. Chazelas. Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Super- lattices. Phys. Rev. Lett., 61, 2472, 1988. [7] G. Binasch, P. Gr ̈unberg, F. Saurenbach, e W. Zinn. Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange. Phys. Rev. B, 39, 4828, 1989. [8] W. P. McCray. How spintronics went from the lab to the iPod. Nature Nanotechology, 4, 2, 2009. [9] J. Nitta, T. Akazaki, H. Takayanagi, e T. Enoki. Gate Control of Spin-Orbit Interaction in an Inverted In0.53Ga0.47As/In0.52Al0.48As Heterostructure. Phys. Rev. Lett, 78, 1335, 1997. [10] S. Datta e B. Das. Eletronic analog of the electro-optic modulator. Appl. Phys. Lett., 56, 665, 1990. [11] Hyun Cheol Koo, Jae Hyun Kwon, Jonghwa Eom, Joonyeon Chang, Suk Hee Han, e Mark Johnson. Control of Spin Precession in a Spin-Injected Field Effect Transistor. Science, 325, 1515, 2009. BIBLIOGRAFIA 79 [12] D. Chiba, M. Sawicki, Y. Nishitani, Y. Nakatani, F. Matsukura, e H. Ohno. Magnetization vector manipulation by electric fields. Nature, 455, 515, 2008. [13] J. K. Furdyna. Diluted magnetic semiconductors. J. Appl. Phys., 64, R29, 1988. [14] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, e D. Ferrand. Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors. Science, 287, 1019, 2000. [15] M. Goryca, D. Ferrand, P. Kossacki, M. Nawrocki, W. Pacuski, W. Ma ́slana, J. A. Gaj, S. Tatarenko, J. Cibert, T. Wojtowicz, e G. Karczewski. Magnetization Dynamics Down to a Zero Field in Dilute (Cd,Mn)Te QuantumWells. Phys. Rev. Lett., 102, 046408, 2009. [16] C. Gould, A. Slobodskyy, D. Supp, T. Slobodskyy, P. Grabs, P. Hawrylak, F. Qu, G. Schmidt, e L.W. Molenkamp. Remanent Zero Field Spin Splitting of Self-Assembled Quantum Dots in a Paramagnetic Host. Phys. Rev. Lett., 97, 017202, 2006. [17] R. M. Abolfath, P. Hawrylak, e I. Zuti ́c. Tailoring Magnetism in Quantum Dots. Phys. Rev. Lett., 98, 207203, 2007. [18] W. Zaleszczyk, E. Janik, A. Presz, P. Dtu ́zewski, S. Kret, W. Szuszkiewicz, J. F. Morhange, E. Dynowska, H. Kirmse, W. Neumann, A. Petroutchik, L. T. Baczewski, G. Karczewski, e T. Wojtowicz. Zn1−xMnxTe Diluted Magnetic Semiconductor Nanowires Grown by Molecular Beam Epitaxy. Nano Lett., 8, 4061, 2008. [19] B. J. van Wees, H. van Houten, C. W. J. Beenakker, J. G. Williamson, L. P. Kouwen- hoven, D. van der Marel, e C. T. Foxon. Quantized conductance of point contacts in a two-dimensional electron gas. Phys. Rev. Lett, 60, 848, 1988. [20] D A Wharam, T J Thornton, R Newbury, M Pepper, H Ahmed, J E F Frost, D G Hasko, D C Peacock, D A Ritchie, e G A C Jones. One-dimensional transport and the quantisation of the ballistic resistance. J. Phsy. C, 21, L209, 1988. [21] I. A. Shelykh, M. Rosenau da Costa, e A. C. Seridonio. Fractional quantization of ballistic conductance in 1D electron and hole systems. J. Phys.: Condens. Matter, 20, 164214, 2008. [22] T. P. Martin, A. Szorkovszky, A. P. Micolich, A. R. Hamilton, C. A. Marlow, R. P. Taylor, H. Linke, e H. Q. Xu. Field-orientation dependence of the Zeeman spin splitting in (In,Ga)As quantum point contacts. Phys. Rev. B, 81, 041303(R), 2010. [23] K. J. Thomas, J. T. Nicholls, M. Y. Simmons, M. Pepper, D. R. Mace, e D. A. Ritchie. Possible Spin Polarization in a One-Dimensional Electron Gas. Phys. Rev. Lett., 77, 135, 1996. BIBLIOGRAFIA 80 [24] A. A. Starikov, I. I. Yakimenko, e K. F. Berggren. Scenario for the 0.7-conductance anomaly in quantum point contacts. Phys. Rev. B, 67, 235319, 2003. [25] G. A. Fiete. Colloquium: The spin-incoherent Luttinger liquid. Rev. Mod. Phys., 79, 801, 2007. [26] Supriyo Datta. Eletronic Transport in Mesoscopic Systems. Cambridge Studies in Semicon- ductor Physics and Microelectronic Engineering. Cambridge University Press, 1995. [27] J. D. M. Vianna, A. Fazzio, e S. Canuto. Teoria Quˆantica de Mol ́eculas e S ́olidos: Simula ̧c ̃ao Computacional. Editora da Livraria da F ́ısica, 2004. [28] P. Hohenberg e W. Kohn. Inhomogeneous electron gas. Phys. Rev., 136, 864, 1964. [29] W. Kohn e L. J. Sham. Self-consistent equations including exchange and correlation effects. Phys. Rev., 140, 1133, 1965. [30] J. A. Gaj, R. Planel, e F. Fishman. Relation of magneto-optical properties of free excitons to spin alignment of Mn2+ ions in Cd1−xMnxTe. Solid State Commun., 29, 435, 1979. [31] J. A. Gaj, W. Grieshaber, C. Bodin-Deshayes, J. Cibert, G. Feuillet, Y. Merle d’Aubign ́e, e A. Wasiela. Magneto-Optical study of interface mixing in the CdTe-(Cd,Mn)Te system. Phys. Rev. B, 50, 5512, 1994. [32] W. Grieshaber, A. Haury, J. Cibert, Y. Merle d’Aubign ́e, e A. Wasiela. Magneto-optic study of the interface in semimagnetic semiconductor heterostructures: Intrinsic effect and interface profile in CdTe-Cd1−xMnxTe. Phys. Rev. B, 53, 4891, 1996. [33] P. Kossacki, H. Boukari, M. Bertolini, D. Ferrand, J. Cibert, S. Tatarenko, J. A. Gaj, B. Deveaud, V. Ciulin, e M. Potemski. Photoluminescence of p-doped quantum wells with strong spin splitting. Phys. Rev. B, 70, 195337, 2004. [34] D. K. Ferry e S. M. Goodnick. Transport in Nanostructures. Cambridge Studies in Semi- conductor Physics and Microelectronic Engineering. Cambridge University Press, 2000. [35] X. Aymerich-Humet, F. Serra-Mestres, e J. Mill ́an. A generalized approximation of the Fermi-Dirac Integrals. J. Appl. Phys., 4, 2850, 1983. [36] M. Goano. Series expansion of the Fermi-Dirac Integral Fj (x) over the entire domain of real j and x. Solid-State Electronics, 36, 217, 1993. [37] H. S. Vosko, L. Wilk, e M. Nusair. Acurrate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys., 58, 1200–1211, 1980. [38] Philip L. Taylor e Olle Heinonen. A Quantum Approach to Condensed Matter Physics. CambridgeUniversity Press, 2002. [39] D. Kosloff e R. Kosloff. A Fourier method solution for the time dependent Schr ̈odinger equation as a tool in molecular dynamics. J. Phys. Chem., 52, 35, 1983. [40] R. Kosloff. Time-dependent quantum-mechanical methods for molecular dynamics. J. Phys. Chem., 92, 2087, 1988. [41] M. H. Degani e J. P. Leburton. Single-electron states and conductance in lateral-surface superlattices. Phys. Rev. B, 44, 10901, 1991. [42] M. H. Degani. Stark ladders in strongly coupled GaAs-AlAs superlattices. Appl. Phys. Lett., 59, 57, 1991. [43] M. H. Degani. Electron energy levels in a δ-doped layers in GaAs. Phys. Rev. B, 44, 5580, 1991. [44] M. H. Degani. Electronic properties of multiple Si δ-doping in GaAs. J. Appl. Phys., 70, 4362, 1991. [45] P. L. DeVries. A First Course in Computational Physics. Wiley, New York, 1993. [46] M. B ̈uttiker. Quantized transmission of a saddle-point constriction. Phsy.Rev. B, 41, 7906, 1990. [47] J. P. Perdew e Mel Levy. Extrema of the functional for the energy: Excited states form ground-state theory. Phys. Rev. B, 31, 6264, 1985. [48] Filipe Sammarco. Magnetocondutˆancia de fios quˆanticos interagentes. Disserta ̧c ̃ao de Mestrado, Instituto de F ́ısica de S ̃ao Carlos - USP, 2009. |
Page generated in 0.0088 seconds