Levitação de estados estendidos em sistemas que apresentam efeito hall quântico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

In this work the Ievitation of extended states in two dimensional electron systems in the presence of magnetic field is numerically investigated. Few years after the discovery of the Quantum Hall Effect, Laughlin and Khmelnitskii conjectured that the extended states at the Landau level centers shouId levitate in energy, rising above the Fermi energy, for vanishing magnetic field or sufficiently increasing disorder. This hypothesis Ieads to important consequences to the transport properties of the system, particularly on the magnetic field induced metal-insulator transitions in two dimensions. This conjecture, however, involves many controversial points and, although intensively investigated in the past few years, many open questions remain unanswered. The present work gives some contributions for understanding the problem. The numerical approach uses two dimensional Iattice models treated in a tight-binding framework, considering non interacting electrons. The degree of Iocalization of the electronic states is inferred from Participation Ratios calculations. It was possible to clearly identify the Ievitation of extended states for both disorder models studied: uncorreIated white-noise like and gaussian correlated disorder. Simple expressions for the magnitude of Ievitation as a function of either magnetic field or disorder could be obtained. These quantitative analysis Iead to comparisons among different disorder models, as well as Landau band indexes, concerning the Ievitation. The present results shed some Iight on the building of the actual Phase Diagram for the Quantum HalI Effect

ASSUNTO(S)

niveis de energia fisica do estado solido hall efeito quantico de

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