Banca de DEFESA: Eronildo Cornelio de Castro

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Eronildo Cornelio de Castro
DATE: 24/11/2022
TIME: 14:30
LOCAL: On-line
TITLE:

Exciton valley dynamics of van der Waals Heterostructures for by transition metal
dichalcogenide (DMTS-2H)

KEY WORDS:

Heterostructures of TMD, éxcitons, optical properties, veletronics, spintronics.

PAGES: 135
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with general formula MX2, where
M=W/Mo and X=S/Se/Te constitute an ideal platform for the exploration and control of physical
properties of matter at the nanoscale, opening new horizons for applications in electronic and
photonic devices. These materials are found in nature in volumetric form and, similar to graphene,
can be synthesized in layers of atomic thickness, allowing access to phenomena originating from
the quantum confinement typical of low dimensional materials. TMD monolayers have
semiconductor characteristics and exhibit direct gap at the non-equivalent points K and K’ of the
Brillouin zone. Due to spatial confinement and reduced dielectric shielding, these materials have
strong Coulombian interaction, so that the photoluminescence spectrum is dominated by strongly
bonded electron-hole pairs (éxcitons). Furthermore, the time reversal asymmetry and the strong
spin-orbit coupling (SOC) enable the selective excitation of valleys via circularly polarized light
and, consequently, the coupling of the spin and pseudo spin degrees of freedom of the valley. These
properties favor the control of the ecciton dynamics in the valley of the nanostructure (monolayer,
bilayer, and heterolayer) and dazzle new perspectives for applications in valetronics and spintronics.
The studies in this subarea of condensed matter still need to be deepened in order to overcome some
challenges that still persist, such as the short lifetime of the excisitons and the valley coherence (of
the order of ps), generated by the strong hybridization between the wave functions of electrons and
holes. However, recent studies have observed the possibility of interlayer dexciton formation, both
in bilayers and in heterostructures, inheriting the spin and valley degrees of freedom of intra-layer
dexcitons in monolayers of TMDs. This new excitonic species exhibit recombination and scattering
interval times (tens of ns), much longer than the characteristic times of the intra-layer excitons.
While monolayers of TMDs have already been extensively studied, heterostructures are still poorly
explored, thus conferring a great motivation for our research. In this context, we propose a
theoretical model capable of describing the dynamics of éxcitons in the valleys of a van der Waals
heterostructure formed by WS2/MoS2. Our model has allowed us to deepen our understanding of the
mechanisms of interlayer exciton scattering by studying the emission properties, with the
photoluminescencespectrum (PL) and the valley polarization (VP). The results of our study are of
high relevance, either by presenting new results for the lifetimes of excitons, especially of the dark
interlayer type, with a high degree of polarization (close to one unit), or by the presentation of
techniques that made feasible in the studies contributing to the progress of this promising line of
research.

BANKING MEMBERS:
Externo à Instituição - AUGUSTO MIGUEL ALCALDE MILLA - UFU
Presidente - 119.509.191-53 - ANTONIO LUCIANO DE ALMEIDA FONSECA - UPS
Externo ao Programa - 1705218 - BERNHARD GEORG ENDERS NETO
Externo à Instituição - GESIEL GOMES SILVA - IFGO
Interna - 1149379 - HELENA DE SOUZA BRAGANCA ROCHA