Banca de DEFESA: FELIPE MARTINS FELIX

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE: FELIPE MARTINS FELIX
DATA: 05/09/2025
HORA: 09:00
LOCAL: Remota (On-line)
TÍTULO: Propriedades eletrônicas e magnéticas do composto S-grafeno.
PALAVRAS-CHAVES: Propriedades eletrônicas e magnéticas do composto S-grafeno.
PÁGINAS: 28
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

In the present work, the electronic and magnetic properties of
S-graphene, a two-dimensional carbon allotrope, were investigated using the
repulsive Hubbard model solved within the Hartree-Fock approximation
(mean-field theory) and first-principles calculations based on Density Functional
Theory (DFT). Initially, the electronic band structure of S-graphene was
analyzed using the tight-binding model, varying some of the hopping terms,
taking into account the symmetry of the unit cell. We observed that the
modulation of these parameters is crucial for the electronic behavior of the
material, which can exhibit insulating, semiconducting, or metallic phases. We
also identified the presence of flat bands and Dirac cones, evidencing the
influence of the hopping terms on the system's electronic structure. There is a
specific situation where the energy gap disappears, leading the system to a
metallic phase characterized by the overlap of two flat bands at the Fermi level.

The investigation of the magnetic properties was carried out employing the
Hubbard model in the Hartree-Fock approximation. The site-magnetization
curves as a function of the electronic interaction U revealed a continuous phase
transition from a paramagnetic to an antiferromagnetic state, characteristic of a
second-order transition. The phase diagram obtained via mean field identified
three distinct phases: semimetallic (SM), band insulator, and antiferromagnetic
insulator (AFMI). We verified that in these phase transitions, the critical value of
the electronic interaction U can vary between (0.0 − 1.95), demonstrating the
Cinfluence of the hopping terms on specific bonds at the critical thresholds of U .
CWe expect that the variation of the hopping terms can be realized by altering the
distances between the lattice sites, which can be achieved by applying a
uniaxial force (strain) to the cell. The first-principles results, obtained via DFT,
corroborated the mean-field predictions. The analysis of the total energy of the
system as a function of the strain applied in the x-direction of the S-graphene
unit cell revealed that, in an intermediate deformation region, considering spin
polarization (SP) results in a lower energy state compared to the system without
spin polarization (NP). This evidenced the emergence of a magnetically ordered
phase. Additionally, the spatial distribution of magnetization indicated that the
central sites of the S-graphene unit cell are primarily responsible for the
magnetic properties, confirming the mean-field model's predictions. In summary,
this study demonstrated that the application of strain to the S-graphene
structure plays a crucial role in the variation of its electronic and magnetic
properties, with the presence of flat bands and electronic interaction favoring
the emergence of magnetic phases. As a perspective, the Monte Carlo method
can be applied to validate and deepen the understanding of the results obtained
by mean field and DFT.

MEMBROS DA BANCA:
Interno - 2056226 - CLEANIO DA LUZ LIMA
Interno - 1548848 - EDUARDO COSTA GIRAO
Presidente - 423297 - JOSE PIMENTEL DE LIMA
Interno - 1340442 - RAMON SAMPAIO FERREIRA
Externo à Instituição - 063.***.***-07 - SEBASTIÃO DOS ANJOS SOUSA JUNIOR - UH