Dissertação de Mestrado #584: Pedro Gonçalves

Structural and electronic transformations upon heating of the Topological Insulator Bi2Se3

Autor: Pedro Henrique Rezende Gonçalves

Banca Avaliadora

Rogério Magalhães Paniago (orientador)

Física - UFMG

Ângelo Malachias de Souza (coorientador)

Física - UFMG

Hélio Chacham

Física - UFMG

Edmar Avellar Soares

Física - UFMG

Orientadores

Rogério Magalhães Paniago (orientador)

Departamento de Física - UFMG

Ângelo Malachias de Souza (coorientador)

Departamento de Física - UFMG

Resumo do Trabalho

The goal of this work was to observe and interpret the transformations that occur upon heating Bi2Se3 at temperatures up to 350oC . X-ray diffraction and Scanning Tunneling Microscopy (STM) techniques were used to observe these transformations. X-ray measurements revealed that upon heating there is a coexistence of a major Bi2Se3 phase (a three-dimensional topological insulator) and a conducting phase with a structure composed of five Bi2Se3 quintuple-layers followed by a bilayer of Bismuth, leading to an overall Bi4Se5 stoichiometry. Density Functional Theory calculations showed that whereas Bi2Se3 is a topological insulator Bi4Se5 is a conventional conductor with several van Hove singularities near the Fermi level. STM measurements of the surface of this material showed the presence of hexagonal Bi4Se5 domains (~200nm) terminated in Bismuth bilayers embedded in a Bi2Se3 matrix. Low temperature scanning tunneling spectroscopy revealed that the bilayer termination exhibits a conducting behavior, with a corresponding conductor-like density of states, presenting no band gap. STS also showed that the bilayer and Bi2Se3 are in electrical contact, with the possibility of the presence of a topological state at the edge of the bilayer, since Bismuth islands are two-dimensional topological insulators.