1,720,958 research outputs found
Coherent phenomena in exciton–polariton systems
No full textExciton-polariton systems, formed through the strong coupling of excitons and photons, provide a unique platform for investigating quantum coherence and collective dynamics in solid-state systems. These hybrid quasiparticles combine photonic and excitonic characteristics, enabling phenomena such as Rabi oscillations, long-distance coherent energy transfer, ballistic energy transport, and Bose-Einstein condensation. Their ability to sustain macroscopic quantum coherence, alongside their sensitivity to environmental and system-engineering factors, highlights their potential for advancing both fundamental quantum science and practical applications, including nanophotonics, energy harvesting, and quantum technologies. This review aims to offer a comprehensive exploration of coherent phenomena in exciton-polariton systems, spanning theoretical foundations, experimental realizations, and applications. Key topics include the dynamics of strong light-matter coupling, the role of vibrational modes and energetic disorder, and the interplay between coherence and dissipation. Advances in ultrafast spectroscopy and quantum electrodynamics models have been pivotal in uncovering polaritonic behavior and optimizing system performance. Despite significant progress, challenges remain in maintaining coherence and addressing the effects of dissipation and disorder. By overcoming these hurdles, exciton-polariton systems promise transformative technological applications and deeper insights into quantum phenomena, positioning them as a cornerstone in the future of quantum science and technology
Direct quantification of the plasmon dephasing time in ensembles of gold nanorods through two-dimensional electronic spectroscopy
No full textIn this study, we used two-dimensional electronic spectroscopy to examine the early femtosecond dynamics of suspensions of colloidal gold nanorods with different aspect ratios. In all samples, the signal distribution in the 2D maps at this timescale shows a distinctive dispersive behavior, which can be explained by the interference between the exciting field and the field produced on the nanoparticle's surface by the collective motion of electrons when the plasmon is excited. Studying this interference effect, which is active only until the plasmon has been dephased, allows for a direct estimation of the dephasing time of the plasmon of an ensemble of colloidal particles. Our findings provide insight into the fundamental behavior of plasmonic states and highlight the potential of two-dimensional electronic spectroscopy in uncovering ultrafast and coherent optical phenomena at the nanoscale
Coherent and Incoherent Ultrafast Dynamics in Colloidal Gold Nanorods
No full textThe study of the mechanisms that control the ultrafast dynamics in gold nanoparticles is gaining more attention, as these nanomaterials can be used to create nanoarchitectures with outstanding optical properties. Here pump-probe and two-dimensional electronic spectroscopy have been synergistically employed to investigate the early ultrafast femtosecond processes following photoexcitation in colloidal gold nanorods with low aspect ratio. Complementary insights into the coherent plasmonic dynamics at the femtosecond time scale and incoherent hot electron dynamics over picosecond time scales have been obtained, including important information on the different sensitivity to the pump fluence of the longitudinal and transverse plasmons and their different contributions to the photoinduced broadening and shift
Signatures of a Conical Intersection in Two-Dimensional Spectra of a Red-Absorbing Squaraine Dye
No full textSquaraine dyes are promising for dye-sensitized solar cells (DSSCs) due to their strong absorption in the red and near-infrared regions. However, their ultrafast photophysical behavior remains poorly understood. Using two-dimensional electronic spectroscopy (2DES) and ab initio computations, we reveal signatures of a conical intersection (CI) governing excited-state dynamics in a prototypical squaraine dye. This sub-200 fs decay pathway may hinder squaraine performance as dye-sensitizers. Our results provide experimental evidence of a sloped CI landscape and elucidate the role of at least two vibrational modes strongly coupled to electronic degrees of freedom. The passage through a CI emerges as a key relaxation mechanism, shedding light on the complex photophysics of these dyes
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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