Banca de DEFESA: David de Sousa Brandão

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : David de Sousa Brandão
DATE: 07/06/2023
TIME: 14:00
LOCAL: Auditório do IF
TITLE:

Excitonic behavior and topological properties in low-dimensional systems

KEY WORDS:

Topological Materials; Phase transition; Exciton; Heterostructures; Quantum Information; Scattering.

PAGES: 120
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

This thesis aims to address new properties and behaviors in low-dimensional systems, which can be divided into two branches: (i) new topological properties found in a one-dimensional electron system with Rashba and Dresselhaus spinorbit interaction, periodically modulated in space, and (ii) manipulation of the valley degree of freedom in two-dimensional materials with inversion asymmetry and potential use as a carrier of quantum information. In the first work we have investigated the phase diagram of a one-dimensional band insulator with spin-orbit coupled electrons, supporting trivial, and topological gapped phases separated by intersecting critical surfaces. The intersections define multicritical lines across which the ground-state energy becomes nonanalytical, concurrent with a closing of the band gap, but with no phase transition taking place. This finding challenges the standard theory of quantum phase transitions according to which a nonanalyticity in the ground-state energy implies a quantum phase transition. Regarding quantum information, we studied a two-level exciton qubit that takes into account the valley degree of freedom. In this scenario, the two valley states are mixed by the intervalley exchange Coulomb interaction and can be tuned by an external magnetic field. We observed that the intensity and sign of the external magnetic field affect the valley pseudospin for different exciton momentum. Finally, We have worked with optical excitonic and valleytronics in two dimensional (2D) materials. We have so far obtained results for the dynamics and scatterings of excitons between excitonic states in 2D van der Walls transition metal dichalchogenides heterostructures MoS2/WS2. We have also investigated the magnetic proximity effect by tuning the valley polarization, as well as the photoluminescence of interlayer excitons, singlets, and long-living triplets. We found that crossing their energies for certain exchange field values gives rise to a photoluminescence peak signature near this critical field. The large valleysplitting energy plays an important role in the valley polarization.

BANKING MEMBERS:
Externo à Instituição - PEDRO PAULO DE MELLO VENEZUELA - UFF
Interno - 3272139 - ALEXANDRE CAVALHEIRO DIAS
Presidente - 1767433 - MARIANA MALARD SALES ANDRADE
Externo ao Programa - 1260083 - PAULO EDUARDO DE BRITO
Externo à Instituição - WEI CHEN - PUC - RJ