Banca de DEFESA: SERGIO MIKAEL VERAS DE SENA ROSA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: SERGIO MIKAEL VERAS DE SENA ROSA
DATA: 30/04/2024
HORA: 14:00
LOCAL: Remota
TÍTULO: Magnetismo e Supercondutividade em Sistemas Frustrados
PALAVRAS-CHAVES: superconductivity, frustration, magnetism, charge-density wave, Quantum Monte Carlo.
PÁGINAS: 25
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

n this thesis, we investigate the XY model (s=1/2) with transverse field on the diamond chain, by considering anisotropic exchange parameters between nearest neighbour spins. The Hamiltonian was fermionized by introducing the Jordan-Wigner transformation and, due to the presence of quartic terms no exact solution for the model can be obtained in terms on non-interacting férmions. An approximate solution of the model was obtained within the Harttree-Fock approach, and by analyzing the behavior of the induced and spontaneous magnetization as a functions of the field, we study the magnetic properties of this frustrated quantum spin chain at temperature zero as well as at non-zero temperature. The results were compared with the exact ones obtained for
finite chains by exact diagonalization and by using the DMRG technique too, in order to verify reliability of the approximation. We build a phase diagram γ × h (anisotropy × magnetic field) at zero temperature and the system has at least one and at most three quantum phase transitions. We also analyzed the behavior of induced magnetization as a function of field and temperature, we also analyzed the behavior of induced magnetization as a function of field and temperature, as well as, the asymptotic behavior of static correlation, validating the calculation of spontaneous magnetization. In parallel, we explored the attractive Hubbard model on the kagome lattice, applying the Determinantal Quantum Monte Carlo technique and we analyzed the s-wave pairing functions for the density ρ = 4/3, showing that the system presents long-range correlation at low temperatures. We also determine the superconducting critical temperature. Next, we carried out an analysis outside the ρ = 4/3 region, varying the hopping t′, where we found the presence of a gap close to the 2/3 density region. However, it is not clear what
phase this is; we therefore assume it is a CDW or VBS phase. We hope that these results are relevant for the study of these ternary metals, in particular, AV3Sb5. Therefore, based on this, we suggest a more detailed study of this region as future perspectives, with the aim of revealing the nature of this insulating phase. Keywords: XY model, Hartree-Fock approximation, Jordan-Wigner transformation,

 

MEMBROS DA BANCA:
Externo à Instituição - EDILBERTO OLIVEIRA SILVA - UFMA
Interno - 1548848 - EDUARDO COSTA GIRAO
Interno - 1446938 - FRANCISCO WELINGTON DE SOUSA LIMA
Interno - 2643659 - IRISMAR GONCALVES DA PAZ
Presidente - 423297 - JOSE PIMENTEL DE LIMA
Externo à Instituição - MARCELLO BARBOSA DA SILVA NETO - UFRJ
Externo à Instituição - MARCELO LEITE LYRA - UFAL