Twisted-light-induced intersubband transitions in quantum wells at normal incidence

We examine theoretically the intersubband transitions induced by laser beams of light with orbital angular momentum (twisted light) in semiconductor quantum wells at normal incidence. These transitions become possible in the absence of gratings thanks to the fact that collimated laser beams present a component of the light's electric field in the propagation direction. We derive the matrix elements of the light-matter interaction for a Bessel-type twisted-light beam represented by its vector potential in the paraxial approximation. Then, we consider the dynamics of photo-excited electrons making intersubband transitions between the first and second subbands of a standard semiconductor quantum well. Finally, we analyze the light-matter matrix elements in order to evaluate which transitions are more favorable for given orbital angular momentum of the light beam in the case of small semiconductor structures.Comment: 9 pages, 2 figure

Photoexcitation of graphene with twisted light

We study theoretically the interaction of twisted light with graphene. The light-matter interaction matrix elements between the tight-binding states of electrons in graphene are determined near the Dirac points. We examine the dynamics of the photoexcitation process by posing the equations of motion of the density matrix and working up to second order in the field. The time evolution of the angular momentum of the photoexcited electrons and their associated photocurrents are examined in order to elucidate the mechanisms of angular momentum transfer. We find that the transfer of spin and orbital angular momentum from light to the electrons is more akin here to the case of intraband than of interband transitions in semiconductors, due to the fact that the two relevant energy bands of graphene originate from the same atomic orbitals.Comment: 18 pages, 4 figure

Efficient spin control in high-quality-factor planar micro-cavities

A semiconductor microcavity embedding donor impurities and excited by a laser field is modelled. By including general decay and dephasing processes, and in particular cavity photon leakage, detailed simulations show that control over the spin dynamics is significally enhanced in high-quality-factor cavities, in which case picosecond laser pulses may produce spin-flip with high-fidelity final states.Comment: 6 pages, 4 figure

A systematic review of life cycle sustainability assessment: current state, methodological challenges, and implementation issues

The life cycle sustainability assessment (LCSA) is a tool to assess sustainability from a life cycle perspective, which has been receiving increased attention over the years. This work presents a systematic review of the current application of LCSA, presenting the foundations, main methods, current operationalization state, and major challenges to its broad implementation. The review protocol considered the search of keywords in Scopus and Web of Science databases. The search has considered the literature published or in the press until December 2018, resulting in the selection of 144 articles written in English. Of those, 71 articles operationalize LCSA in real case studies, while the remaining consist of review, viewpoint, and methodological development articles. This review demonstrates that the use of LCSA has been increasing in recent years. Today, the most applied approach is to consider LCSA as the sum of life cycle assessment, life cycle costing, and social life cycle assessment because it is built on the methodologies that already exist and are under continuous development. However, the lack of harmonization of the methodology is a central challenge to its operationalization. Therefore, LCSA still requires further improvement in, among others, definition of coherent system boundaries, the development of robust databases to allow the assessment of economic and social perspectives, definition of impact categories that allow comparability between studies, development of impact assessment methods, development of methods to carry out uncertainty analysis, and communication strategies. Besides, further case studies should be developed to support the improvement of the methodology and a better understanding of the interaction of the environmental, economic, and social aspects.publishe

Coherent optical control of spin-spin interaction in doped semiconductors

We provide a theory of laser-induced interaction between spins localized by impurity centers in a semiconductor host. By solving exactly the problem of two localized spins interacting with one itinerant exciton, an analytical expression for the induced spin-spin interaction is given as a function of the spin separation, laser energy, and intensity. We apply the theory to shallow neutral donors (Si) and deep rare-earth magnetic impurities (Yb) in III-V semiconductors. When the photon energy approaches a resonance related to excitons bound to the impurities, the coupling between the localized spins increases, and may change from ferromagnetic to anti-ferromagnetic. This light-controlled spin interaction provides a mechanism for the quantum control of spins in semiconductors for quantum information processing; it suggests the realization of spin systems whose magnetic properties can be controlled by changing the strength and the sign of the spin-spin interaction.Comment: 10 pages, 5 figure

Twisted-light-induced optical transitions in semiconductors: Free-carrier quantum kinetics

We theoretically investigate the interband transitions and quantum kinetics induced by light carrying orbital angular momentum, or twisted light, in bulk semiconductors. We pose the problem in terms of the Heisenberg equations of motion of the electron populations, and inter- and intra-band coherences. Our theory extends the free-carrier Semiconductor Bloch Equations to the case of photo-excitation by twisted light. The theory is formulated using cylindrical coordinates, which are better suited to describe the interaction with twisted light than the usual cartesian coordinates used to study regular optical excitation. We solve the equations of motion in the low excitation regime, and obtain analytical expressions for the coherences and populations; with these, we calculate the orbital angular momentum transferred from the light to the electrons and the paramagnetic and diamagnetic electric current densities.Comment: 11 pages, 3 figure

'É melhor em conjunto': uma análise de clusters à auto-liderança e a sua relação com a inovação individual em enfermeiros hospitalares

Self-leadership is designed to influence positive outcomes like individuals’ innovative capacity in the workplace. Nevertheless, research on the relationship between self-leadership and individual innovation has failed to determine which self-leadership strategies contribute to innovation. Thus, this study aims to: explore the existence of different profiles of self-leadership strategies in hospital nurses and, test if these different profiles have different effects on individuals’ ability to be innovative. 288 nurses participated in this study. Firstly, data was analysed using Cluster analysis. Secondly, to verify the significance of the association between self-leadership clusters and individual innovation chi-square tests were conducted and the adjusted residuals were considered. Results revealed the existence of 3 different clusters of self-leadership, and that individual innovation is more frequent when all self-leadership strategies are used. The findings suggest that self-leadership strategies vary between individuals and that they all should be fostered in order to promote individual innovation.info:eu-repo/semantics/publishedVersio

Teams as Complex Adaptive Systems: Reviewing 17 Years of Research

At the turn of the century, Arrow, McGrath, and Berdahl portrayed teams as complex adaptive systems (CAS). And yet, despite broad agreement that this approach facilitates a better understanding of teams, it has only now been timidly incorporated into team research. To help fully incorporate the logic of teams as CAS in the science of teams, we review extant research on teams approached from a nonlinear dynamical system theory. Using a systematic review approach, we selected 92 articles published over the last 17 years to integrate what we know about teams as CAS. Our review reveals the evidence supporting teams as CAS, and the set of analytical techniques to analyze team data from this perspective. This review contributes to teams’ theory and practice by offering ways to identify both research methods and managing techniques that scholars and practitioners may apply to study and manage teams as CAS