Banca de QUALIFICAÇÃO: DENILSON DE MORAIS SILVA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : DENILSON DE MORAIS SILVA
DATE: 05/03/2024
TIME: 14:00
LOCAL: Instituto de Física - UFAL
TITLE:

PROPERTIES OF POLARONS UNDER THE INFLUENCE OF EXTERNAL FIELDS

KEY WORDS:

Polaron, nonlinearity, polymer, electric field, homodimer, magnetic field.

PAGES: 90
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUBÁREA: Física da Matéria Condensada
SPECIALTY: Estados Eletrônicos
SUMMARY:

In the present text, we investigate three distinct systems with nonlinear properties and action of external fields. In the first work, we study the polaron formation and dynamical on homodimer polymer chains, which stiff cyclic structures allow conduction electron interaction through electron-lattice coupling. We observe a transition from itinerant polarons to stationary around initial position while we increases the coupling parameter, when its velocities decrease until null. Analysis of physical measurements show that localization degree increases with coupling parameter, while energy gaps between nearest-neighbor change long time behavior. The critical coupling parameter decreases when gap increases, according to complementary analysis of initial polaron velocity to some gaps energy values, allowing diagram elaboration that discriminates both regimes. In the second works, we study polaron formation and dynamical in a unidimensional molecular crystal subject to the influence of statical and harmonic electric fields. The polymer has intermolecular vibrations coupled with conduction electron. Exploring fields sets that promote directional transport, we show the small polarons formation traveling with velocity close to crystal sound velocity, when coupling parameter reaches a specific value. With weak coupling, the dynamical is similar to direction free electron caused of fields, but strong enough coupling, the polaron remains stationary around the initial position. Exploring distinct electric fields magnitudes and electron-lattice coupling, we make a phases diagram showing that critical couplings of transition between the states increase with the field, revealing also the metastable polaron formation. In the last work we study an electron on both square and honeycomb two-dimensional lattices subject to a constant magnetic field. We formulated Schrödinger equations for both lattices considering the field influences. When analyzing the electronic Gaussian wavepacket initially at rest, we identified distinct regimes, including regular breathing partners or at rest on eigenstate configuration when the width is magnetic length, the lowest Landau level. With electron initial momentum around Γ point, appear cyclotron dynamics with measurements of oscillations orbital radius and frequency with agreement with the semiclassical approach. The oscillations turn more complex when we distance significantly of Γ point, showing dynamics regimes with vortex and interference partners, emphasizing unique characteristics of lattices structures. 

COMMITTEE MEMBERS:
Presidente - 1120933 - MARCELO LEITE LYRA
Interno(a) - 2318874 - FRANCISCO ANACLETO BARROS FIDELIS DE MOURA
Interno(a) - 1366820 - IRAM MARCELO GLERIA