Banca de QUALIFICAÇÃO: SERGIO MIKAEL VERAS DE SENA ROSA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE: SERGIO MIKAEL VERAS DE SENA ROSA
DATA: 17/12/2021
HORA: 10:00
LOCAL: Plataforma Google Meet
TÍTULO: Modelo XY sobre a cadeia diamante,
PALAVRAS-CHAVES: Diamond chain, XY model, Hartree-Fock approximation.
PÁGINAS: 25
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

We consider the s = 1/2 transverse field XY model on the frustrated diamond chain, con-
sidering anisotropic exchange parameters between nearest neighbour spins. To this end, we

employ three different methodologies: mean-field approximations, and state-of-the-art exact
diagonalizations (ED), and density matrix renormalization group (DMRG) simulations. Within

a mean-field theory, the Hamiltonian is fermionized by introducing the Jordan-Wigner trans-
formation, and the interacting (many-body) terms are approximated to single-particle ones by

a Hartree-Fock approach. We analyze the behavior of the induced and spontaneous magnetiza-
tion as functions of the external field, investigating the magnetic properties at the ground state,

and at finite temperatures. Interestingly, the mean-field results are in reasonable agreement with
the ED and DMRG ones, in particular for the distorted chain, or at an intermediate/large spin
anisotropy parameter. As our key results, we present phase diagrams anisotropy × magnetic
field at zero temperature, discussing the emergence of phases and its quantum critical points.
Finally, our analysis at finite temperature provides a range of parameters in which an unusual
behavior of the induced magnetization occurs – with it increasing as a function of temperature.
This work presents a global picture of the XY model on the diamond chain, which may be
useful to understand features of magnetism in more complex geometries.

MEMBROS DA BANCA:
Interno - 1548848 - EDUARDO COSTA GIRAO
Presidente - 423297 - JOSE PIMENTEL DE LIMA
Externo ao Programa - 010.453.033-21 - NATANAEL DE CARVALHO COSTA - UFPI
Externo ao Programa - 344.235.407-20 - RAIMUNDO ROCHA DOS SANTOS - UFRJ