THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
Grafos para Contextualidade, Grafos Coloridos para Não-localidade
Prof. Dr. Marcelo Terra Cunha – IMECC -Unicamp
Abstract:
A teoria quântica alia duas características instigantes: sucesso preditivo e fundamentação controversa. Uma das mais dramáticas distinções entre a teoria quântica e teorias clássicas está a não-localidade, no sentido de John Bell: experimentos de correlação entre partículas distantes podem exibir correlações inconsistentes com noções muito básicas que acompanharam o pensamento ocidental por séculos. Ainda que a não-localidade seja a versão mais dramática dessa distinção entre correlações clássicas e quânticas, ela é só um caso particular do que se chama contextualidade. Nessa palestra pretendemos explicar o que é contextualidade, apresentar surpreendentes contribuições da teoria de grafos ao estudo de contextualidade em geral e não-localidade, em particular, abordando de maneira introdutória trabalhos recentes e futuros.
Date: 2/October/2015 – (friday) – Place: Sala 212 – Auditorio do Departamento de Física – Time: 10h15min
THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
Domain growth and dipolar bias in magnetic thin films coupled to aperiodic pinning potential
Prof. Dr. Rafael Leonardo Novak
UFSC / Campus Blumenau
Abstract:
Domain walls are playing an increasingly important role in new, experimental data storage technologies, as they can be easily manipulated by current and/or magnetic and electric fields. Controllable pinning is paramount for these applications and extrinsic, non-traditional sources of domain wall pinning, such as spatially varying dipolar fields and focused ion beam irradiation, have been proposed as means of tailoring magnetization reversal and domain wall pinning over short length scales. Here we detail magneto-optical studies of domain wall motion and domain wall mediated switching in a continuous, magnetically soft, ultrathin [Pt/Co]x (x = 1 or 2) film with perpendicular anisotropy which is coupled to an array of harder [Co/Pt]4 magnetic nanodots via dipolar interaction across a thin Pt spacer. In the absence of nanodots, the domain wall dynamics is dominated by thermally activated creep, while the stray field underneath the nanodot array gives rise to a spatially periodic pinning potential for domain walls propagating through the underlying continuous film which leads to field-asymmetric reversal and exchange-bias-like phenomena. We observe strikingly different domain wall morphologies depending on the field polarity and the strength of the coupling between the nanodots and the underlying layer, as well as domain wall velocity differences of up to 3 orders of magnitude and transitions from compact faceted to percolation-like dendritic domain wall propagation modes. We show that the average domain wall mobility of a magnetic thin film can be controlled by an external parameter, in this casethe magnetization state of an array of magnetic nanodots, opening the possibility of controlling domain wall propagation paths in thin magnetic films.
Date: 08/July/2015 – (wednesday) – Place: Sala 212 – Auditório do Departamento de Física- Time: 16 horas
THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
O MUNDO PLANO DOS ISOLANTES TOPOLÓGICOS
Adalberto Fazzio – USP
Abstract:
O modelo e a linguagem para descrever a estrutura eletrônica de materiais foram e, ainda, são baseados na teoria de bandas desenvolvida primeiramente por Felix Bloch, em 1929. Nessa descrição, isolantes são caracterizados por um conjunto de níveis de energia completamente “ocupados” e um conjunto de níveis de energia “vazios” separados por um gap de energia e, de acordo com modelos semiclássicos para o transporte eletrônico, fazem o material eletricamente inerte. A descoberta do efeito Hall Quântico (QH) em sistemas eletrônicos de duas dimensões (2D) foi a ponta do iceberg para classificar fenômenos que parecem violar a definição de estado isolante, ou seja, sistemas com gap de energia no bulk exibiam propriedades de transporte não triviais. Recentemente, uma nova classe de isolantes topológicos preditos teoricamente e realizados experimentalmente tem sido objeto de intenso estudo. Esses isolantes topológicos têm um gap isolante no bulk, mas apresentam estados de superfícies protegidos devido à simetria de reversão temporal (TRI). Neste colóquio, apresentarei esses novos materiais que, somente por causa das interações spin-órbita, levam a uma fase da matéria chamada de Quantum Spin Hall (QSH), topologicamente distinto de outros estados isolantes que conhecemos. Em particular, irei focar em sistemas 3D. Ao final, mostrarei alguns resultados obtidos por nosso grupo de pesquisa através dos cálculos de primeiros princípios baseados na teoria do funcional da densidade (DFT).
Date: 3/July/2015 – (friday) – Place: Sala 212 – Auditório do Departamento de Física– Time: 10h15min
THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
GRAPHENE-BASED NANOSTRUCTURES: PLASMONICS IN THE THZ RANGE
Mikhail Igorevich Vasilevskiy
Universidade do Minho – Portugal
Abstract:
The talk will consist of two parts dedicated, respectively, to linear and non-linear optical properties of graphene in the terahertz (THz) spectral range, related to its unique electronic spectrum (gapless and linear in momentum).
In the first part, surface plasmon-polaritons (SPPs) in graphene will be discussed along with several possible ways of their coupling to propagating electromagnetic waves in the THz range, such as (i) the attenuated total reflection (ATR) method employing a prism, (ii) graphene-based gratings or graphene monolayers with modulated conductivity, (iii) a metallic stripe or a needle tip on top of the graphene layer. Potentially interesting for applications SPP effects, such as switching, modulation and polarization of THz radiation will be considered.
In the second part some effects of the optical non-linearity of the surrounding medium or of graphene itself will be considered, including mixed polariton solitons of TE type, optical bistability of a graphene layer, and lattice solitons in a multilayer stack of graphene sheets.
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THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
- University of Caen-Basse Normandie (France)
Sub-saturation equation of state for Core-Collapse Supernovae and Neutron Stars
Francesca Gulminelli – LPC/Ensicaen and University of Caen (France)
Abstract:
The construction of a realistic equation of state for dense matter as it can be found in core-collapse supernovae and neutron stars is a formidable task which is not yet completely achieved. The structure of very high density matter in the neutron star core is by far the most uncertain part of the EoS modeling. However, even in the least exotic regime of sub-saturation matter, where the degrees of freedom are purely nucleonic and relatively well-known, the presence of clustering due to the Coulomb quenching of the nuclear liquid-gas phase transition requires beyond mean-field methods properly treating all the complexity of nuclear structure, in a regime of neutron-rich matter where no experimental data exist to validate the available effective interactions.
Self-consistent mean-field approaches with realistic effective interactions are still routinously applied at zero temperature. This is justified thanks to the Wigner-Seitz structure of stellar matter, which reduces the thermodynamic limit to a single nucleus problem. However, a consistent treatment at finite temperature in principle implies beyond mean-field configuration mixing. This is presently a problem since existing models are either done in the single nucleus approximation, or do not recover the single-nucleus Wigner-Seitz limit of zero temperature.
In this talk we will present a density-functional formalism which, by introducing explicit cluster degrees of freedom, consistently describes the neutron-rich nuclei immersed in the gas of their continuum states in the inner crust, and the nuclear statistical equilibrium of different in-medium modified nuclear species in supernova matter. The influence of the effective interaction, and specifically the density dependence of the symmetry energy, will also be discussed.
Date: 22/May/2015 – (friday) – Place: Sala 212 – Auditório do Departamento de Física– Time: 10h15min
