Banca de DEFESA: ANDERSON DE SOUZA BIBIANO FILHO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : ANDERSON DE SOUZA BIBIANO FILHO
DATE: 20/12/2022
TIME: 14:00
LOCAL: Através de Videoconferência: https://meet.google.com/zeb-ephy-rwz
TITLE:

Kosterlitz-Thouless transition in a mixed-spin ladder under a magnetic field

KEY WORDS:

Transições de fase quântica, Modelo do Hamiltoniano de Heisenberg, Cadeia escada de spin misturado com spin-$1$ e spin-$\frac{1}{2}$.

PAGES: 86
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

At zero temperature, thermal fluctuations are eliminated and phase transitions will occur due to quantum
fluctuations that arise from the Heisenberg uncertainty principle. Magnetic insulators, described by the
Heisenberg model Hamiltonian, are a known class of physical systems that can undergo quantum phase
transitions when submitted to a magnetic field. The magnetic field induces the transition by closing energy gaps
through the Zeeman effect. Examples of these systems are the antiferromagnetic spin-1 chain, the
antiferromagnetic spin-1/2 ladder, the ferrimagnetic mixed spin-1 and spin-1/2 chains and ladders. The
presence of a gap in the energy spectrum leads to a magnetization plateau in the magnetization curve. We use

the density matrix renormalization group to investigate the magnetization curves of the mixed spin-1 and spin-
1/2 ladder, for antiferromagnetic and ferromagnetic couplings between the ladder legs, J0. For J0 > 0, the

ground-state is ferrimagnetic with the total spin equal to 1/3 of the saturation value, in accord with the Lieb-
Mattis theorem. The magnetization curve presents a plateau at 1/3 of the saturation value, 1/3-plateau, since the

ground state has a gap to excitations that increase the total spin by 1 unit. Decreasing J0 below zero, the ground
state is a singlet, but the 1/3-plateau survives down to a critical value J0 = Jc. Given that the gap closes with the
magnetization fixed, it is a transition of the Kosterlitz-Thouless type. To determine Jc, we have made a finite
size scale analysis of the plateau width.

COMMITTEE MEMBERS:
Externo à Instituição - NATANAEL DE CARVALHO COSTA - UFRJ
Interno - 1129671 - MAURICIO DOMINGUES COUTINHO FILHO
Presidente - 2378411 - RENE RODRIGUES MONTENEGRO FILHO