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You searched for subject:(the Kondo effect). Showing records 1 – 2 of 2 total matches.

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1. Lima, Neemias Alves de. Expansão perturbativa regularizada para o efeito Kondo.

Degree: Mestrado, Física Básica, 1998, University of São Paulo

Nas últimas duas décadas a teoria dos sistemas eletrônicos correlacionados teve enorme progresso, que sustentou o paralelo desenvolvimento da pesquisa experimental dos sistemas de férmions pesados. Dada a complexidade do problema proposto pelas correlações fortes, diversas técnicas complementares de cálculo foram desenvolvidas no período. O presente plano se propõe a explorar uma extensão de uma das mais antigas, a técnica do grupo de renormalização numérico (GRN), tratando perturbativamente o modelo de Kondo para uma impureza magnética em um hospedeiro metálico. É bem conhecido que a expansão perturbativa de propriedades físicas, como a susceptibilidade, em termos do acoplamento de troca diverge logaritmicamente próxima da temperatura de Kondo. A abordagem do GRN para isto considera a transformação discreta, T[HN] = HN+1, onde {HN} é uma seqüência de Hamiltonianos. Neste trabalho, para regularizar a expansão da susceptibilidade, usamos um procedimento alternativo considerando a transformação contínua análoga, Tδz[HN(z)] = HN(z+δz), onde z é um parâmetro arbitrário que generaliza a discretização logarítmica do GRN. Ao contrário do procedimento de Wilson, nós esperamos que este novo procedimento possa ser mais facilmente aplicável a Hamiltonianos mais complexos, complementando a diagonalização numérica.

In the last two decades the theory of electronic correlated systems has had an enormous progress, which has sustained the parallel development of the experimental research in heavy fermion systems. Given the complexity imposed by the strong correlations, several techniques appeared. The present work explores an extension of one of the oldest, the Numerical Renormalization Group (NRG), treating perturbatively the Kondo model for a magnetic impurity in a metallic host. It is well known that perturbative expansion of physical properties, like susceptibility, in terms of the exchange coupling diverges logarithmically near the Kondo temperature. The NRG approach for this consider the discrete transformation, T[HN] = HN+1, where {HN}, is a sequence of Hamiltonians. In this work we use an alternative procedure to regularize the expansion, using an analogous continuum transformation Tδz[HN(z)] = HN(z+δz), where z is an arbitrary parameter which generalizes the NRG logarithmic discretization. Unlike Wilson\'s procedure, we hope this new one can be easily applicable to more complex Hamiltonians, complementing the numerical diagonalization.

Advisors/Committee Members: Libero, Valter Luiz.

Subjects/Keywords: Efeito Kondo; Kondo effect; Regularização de expansão perturbativa; Regularization of the perturbative expansion

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APA (6th Edition):

Lima, N. A. d. (1998). Expansão perturbativa regularizada para o efeito Kondo. (Masters Thesis). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03062014-104535/ ;

Chicago Manual of Style (16th Edition):

Lima, Neemias Alves de. “Expansão perturbativa regularizada para o efeito Kondo.” 1998. Masters Thesis, University of São Paulo. Accessed January 25, 2020. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03062014-104535/ ;.

MLA Handbook (7th Edition):

Lima, Neemias Alves de. “Expansão perturbativa regularizada para o efeito Kondo.” 1998. Web. 25 Jan 2020.

Vancouver:

Lima NAd. Expansão perturbativa regularizada para o efeito Kondo. [Internet] [Masters thesis]. University of São Paulo; 1998. [cited 2020 Jan 25]. Available from: http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03062014-104535/ ;.

Council of Science Editors:

Lima NAd. Expansão perturbativa regularizada para o efeito Kondo. [Masters Thesis]. University of São Paulo; 1998. Available from: http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03062014-104535/ ;


University of Lund

2. Deng, Mingtang. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.

Degree: 2013, University of Lund

This thesis focuses on charge transport in semiconductor InSb nanowire quantum devices, including the electron transport, the hole transport, and the Cooper pair transport. Devices in which InSb semiconductor nanowire quantum dots are coupled with normal metals, superconductors or the proximity effect induced topological superconductors are fabricated and measured. Firstly, we have fabricated and measured normal metal contacted InSb nanowire devices. In each of these devices, a quantum dot is formed in the InSb nanowire between the contacts. We report on the magnetotransport measurements performed to these quantum dot devices, and reveal several novel transport features. First, we demonstrate the ambipolar quantum dot devices in which the quantum dots can be tuned from the n-type regime to the p-type regime. The transport measurements in both of the n-type regime and the p-type regime are performed. We also show that two methods can be used to estimate the effective g-factor of the quantum dot, but they can give very different estimation in the presence of a Kondo effect. In the p-type regime of an ambipolar quantum dot, we observe conductance peaks in the stability diagram which can be attributed to the quasi-1D lead states. Secondly, we have fabricated and characterized the superconductor coupled InSb nanowire quantum dots. We probe the density of states of the quasi-particles in the superconductor contacts, via a weakly coupled InSb quantum dot. In the strongly coupled InSb nanowire-superconductor junctions, dissipationless Josephson currents are observed. A SQUIDS device is also fabricated and measured, in which an anomalous modulation of the Josephson current in the magnetic field is observed. In the medium coupling regime, we observe the signatures of the multiple Andreev reflections, the sub-gab bound states, and the Josephson current, interplaying with the Kondo effect. By adjusting the gate voltages, we can control the dot-lead coupling strength and asymmetry. Here, we report the quantum phase transition induced by tuning the dot-lead coupling and the quantum phase transition induced by a magnetic field. We have also found the coupling asymmetry is very important for the observation of the Josephson current. In the magnetic field, the evolution of the Kondo effect enhanced Josephson current is found to be strongly dependent on the energy ratio of Kondo energy and superconducting gap. Finally, an anomalous low-field suppression of the zero-bias conductance peak in the Kondo regime is observed. In the last part of the thesis, we report on our efforts to search for Majorana fermions in solid state systems. Nb-InSb nanowire quantum dot-Nb hybrid devices were fabricated and the transport measurements were performed at low temperatures for these devices. We have observed anomalous zero-bias conductance peaks emerging in finite magnetic fields in the Nb-InSb nanowire quantum dot-Nb hybrid devices as a signature of the Majorana bound states in such hybrid devices. We have also found that the zero-bias conductance…

Subjects/Keywords: Condensed Matter Physics; Multiple Andreev reflection; SQUID; Proximity effect; the Josephson effect; Cooper pair; the Kondo effect; the Zeeman effect; Quantum dot; InSb; Nanowires; Transport; Fysicumarkivet A:2013:Deng; Majorana bound state; Yu-Shiba-Rusinov state; Andreev bound state

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Deng, M. (2013). Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. (Doctoral Dissertation). University of Lund. Retrieved from https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf

Chicago Manual of Style (16th Edition):

Deng, Mingtang. “Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.” 2013. Doctoral Dissertation, University of Lund. Accessed January 25, 2020. https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf.

MLA Handbook (7th Edition):

Deng, Mingtang. “Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.” 2013. Web. 25 Jan 2020.

Vancouver:

Deng M. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. [Internet] [Doctoral dissertation]. University of Lund; 2013. [cited 2020 Jan 25]. Available from: https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf.

Council of Science Editors:

Deng M. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. [Doctoral Dissertation]. University of Lund; 2013. Available from: https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf

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