Induction and reversion of magnetic monopole in concave surfaces of topological insulators

• Ano de defesa: 2016
• Autor(a) principal: Campos, Warlley Hudson
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Monopolo magnético; Superfícies (Física) - Propriedades magnéticas; Física da Matéria Condensada
• Link de acesso: http://www.locus.ufv.br/handle/123456789/9779

In this dissertation we have investigated a new class of materials, recently discovered, that has intriguing properties with substantial prospects of technological applications. These are the so-called topological insulators (TI’s), once their bulks are insulating but with associated wavefunctions carrying non-trivial topology, what provides con- ducting states at their edges protected by time reversal symmetry (TRS). These states are counter propagating relative to their spin, which opens an interesting window for technological applications, such as quantum computation and “spintronics”. By coating the surface of a 3-D TI with a ferromagnetic film, one breaks the TR symmetry and creates a gap in the edge states. This gap gives rise to a half-integer quantized Hall conductivity, leading to the topological magneto-electric effect (TMEE), which consists of both an electric and magnetic response of the material due to an external field, whether electric or magnetic. It is known that an electric charge near the surface of a topological insulator induces an image magnetic monopole inside its bulk, due to the TMEE. We have calculated the magnetic field resulting from a specific configuration, when the topological surface has a negative curvature, particularly in the case of a semi-spherical concavity. Analysing the magnetic field, we show that the image magnetic monopole reverses its sign when the electric charge crosses the focus of the semi-sphere. In addition, there is a line of magnetic charge density in the image charge configuration, which also reverses its sign. These reversions are characteristic features of negative curved surfaces, and cannot happen in perfectly spherical or plane TI’s. When the electric charge is brought near the surface, the local magnetic field then recovers that due to a magnetic monopole alone, as expected, since locally we have a plane surface.