Banca de DEFESA: RODRIGO TARDINI PAULINO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : RODRIGO TARDINI PAULINO
DATA : 04/08/2022
HORA: 14:00
LOCAL: Auditório 801- B do Bloco B do Campus Santo André da Universidade Federal do ABC
TÍTULO:

Tuning the bulk conducting states of the topological insulator Bi2Se3

PÁGINAS: 50
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Estados Eletrônicos
RESUMO:

The Bi2Se3-family of materials are well known thermoelectrics widely applied in industry, that received renewed interest in the last decade as one of the first predicted 3D topological insulators. With a single Dirac cone responsible for the topologically protected surface states and a large band gap of over 200 meV, practical application of relativistic Dirac electrons are being limited by the overwhelming presence of bulk electrons in transport phenomena. Consequently, the suppression of these bulk states is of great interest for technologies of the future, like quantum computing and spintronics. With its origins tracing back to inherent structural defects, the properties of these bulk electrons can be tuned simply by the single crystal growth procedure, without the need of external dopants. The main objective of this dissertation is to utilize the self-flux method to obtain Bi2Se3 single crystals in the entire Bi:Se concentration range available in the phase diagram, looking to fully
explore the different defects present in the structure. Through powder X-ray diffraction (PXRD) and electron dispersive X-ray spectroscopy (EDS), the change in the induced defects was confirmed. Hall effect measurements showed that all samples were n-type, with electron densities ranging from 10^17 cm^(−3) up to 10^19 cm^(−3) in Se and Bi-rich samples, respectively. A dominant electron-phonon scattering at high temperatures resulted in typical metallic behaviour in the resistivity and, with the electron mobility reaching as high as 10^4 cm^2 V^(−1) s^(−1), ionized impurities were found to dominate the scattering effects at low temperatures. Shubnikov-de Haas quantum oscillations in the magnetoresistance unequivocally place the Fermi level within the conduction band and, by comparing the frequency and the Hall effect electron density, the shape of the Fermi surface was reconstructed. Furthermore, careful analysis of the oscillation phase considering the large Zeeman effect of Bi2Se3, classify the bulk electrons as topologically trivial, solving previously contradicting literature results. With samples ranging from high- to low density of electrons, this work also offers a unified view of the bulk states, providing a review of previous results and discussing many of the unanswered questions in the relevant literature.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1671599 - MARCOS DE ABREU AVILA
Membro Titular - Examinador(a) Externo à Instituição - MAURO MELCHIADES DORIA - UFRJ
Membro Titular - Examinador(a) Externo à Instituição - PASCOAL JOSÉ GIGLIO PAGLIUSO - UNICAMP
Membro Suplente - Examinador(a) Interno ao Programa - 1544408 - GUSTAVO MARTINI DALPIAN
Membro Suplente - Examinador(a) Externo à Instituição - EDUARDO GRANADO MONTEIRO DA SILVA - UNICAMP