1,720,957 research outputs found
Cavity Control of Phase Transitions and Nonlinearities in Quantum Materials
No full textThe possibility of engineering the light-matter coupling with optical cavities has recently emerged as a new path to manipulate the collective properties of quantum materials. In this doctoral thesis, we explore the effect of light matter coupling inside a cavity on the complex materials CuGeO3, 1T-TaS2 and SrTiO3 through terahertz spectroscopy. In order to exploit the light matter interaction in cavity confined system, we built a Terahertz Fabry-Pérot resonator that can couple with low energy excitations and subsequently affect the collective behaviours in complex materials. The capability of the setup to tune the cavity fundamental mode at the cryogenic temperatures makes it highly versatile to study a wide range of quantum materials. Firstly, we will show the signatures of vibrational strong coupling in the normal phase of a spin-peierls compound CuGeO3 and the charge density wave(CDW) material 1T-TaS2 when embedded inside a resonant terahertz cavity. Observation of Rabi splitting indicates hybridization between material excitations and fundamental mode of the cavity in the strong coupling regime. Notably, for 1T-TaS2, we reveal a multimode vibrational coupling scenario arising from the coupling between the fundamental cavity mode and multiple charge density wave phonon modes in the dielectric phase of the material. We will then investigate the first order metal-to-insulator phase transition of the CDW material 1T-TaS2 inside a cavity. We unveil that the effective phase transition temperature can be controlled by tuning the cavity frequency and mirror alignment pointing to a scenario in which the cavity can filter the heat load on sample from the electromagnetic environment in a Purcell-like mechanism. Finally, we will discuss the cavity mediated nonlinear reponses in a paraelectric material SrTiO3. The findings suggest that the nonlinearities likely associated with the soft phonon mode, are enhanced within the cavity’s electromagnetic environment hence unveiling the potential to achieve the anharmonic regime of quantum materials without the need for intense lasers.The possibility of engineering the light-matter coupling with optical cavities has recently emerged as a new path to manipulate the collective properties of quantum materials. In this doctoral thesis, we explore the effect of light matter coupling inside a cavity on the complex materials CuGeO3, 1T-TaS2 and SrTiO3 through terahertz spectroscopy. In order to exploit the light matter interaction in cavity confined system, we built a Terahertz Fabry-Pérot resonator that can couple with low energy excitations and subsequently affect the collective behaviours in complex materials. The capability of the setup to tune the cavity fundamental mode at the cryogenic temperatures makes it highly versatile to study a wide range of quantum materials. Firstly, we will show the signatures of vibrational strong coupling in the normal phase of a spin-peierls compound CuGeO3 and the charge density wave(CDW) material 1T-TaS2 when embedded inside a resonant terahertz cavity. Observation of Rabi splitting indicates hybridization between material excitations and fundamental mode of the cavity in the strong coupling regime. Notably, for 1T-TaS2, we reveal a multimode vibrational coupling scenario arising from the coupling between the fundamental cavity mode and multiple charge density wave phonon modes in the dielectric phase of the material. We will then investigate the first order metal-to-insulator phase transition of the CDW material 1T-TaS2 inside a cavity. We unveil that the effective phase transition temperature can be controlled by tuning the cavity frequency and mirror alignment pointing to a scenario in which the cavity can filter the heat load on sample from the electromagnetic environment in a Purcell-like mechanism. Finally, we will discuss the cavity mediated nonlinear reponses in a paraelectric material SrTiO3. The findings suggest that the nonlinearities likely associated with the soft phonon mode, are enhanced within the cavity’s electromagnetic environment hence unveiling the potential to achieve the anharmonic regime of quantum materials without the need for intense lasers
Ultrafast pump-probe phase-randomized tomography
No full textMeasuring fluctuations in matter’s low-energy excitations is the key to unveiling the nature of the non-equilibrium response of materials. A promising outlook in this respect is offered by spectroscopic methods that address matter fluctuations by exploiting the statistical nature of light-matter interactions with weak few-photon probes. Here we report the first implementation of ultrafast phase randomized tomography, combining pump-probe experiments with quantum optical state tomography, to measure the ultrafast non-equilibrium dynamics in complex materials. Our approach utilizes a time-resolved multimode heterodyne detection scheme with phase-randomized coherent ultrashort laser pulses, overcoming the limitations of phase-stable configurations and enabling a robust reconstruction of the statistical distribution of phase-averaged optical observables. This methodology is validated by measuring the coherent phonon response in α-quartz. By tracking the dynamics of the shot-noise limited photon number distribution of few-photon probes with ultrafast resolution, our results set an upper limit to the non-classical features of phononic state in α-quartz and provide a pathway to access non-equilibrium quantum fluctuations in more complex quantum materials
Tunable cryogenic terahertz cavity for strong light–matter coupling in complex materials
Full text linkWe report here the realization and commissioning of an experiment dedicated to the study of the optical properties of light–matter hybrids constituted of crystalline samples embedded in an optical cavity. The experimental assembly developed offers the unique opportunity to study the weak and strong coupling regimes between a tunable optical cavity in cryogenic environment and low energy degrees of freedom, such as phonons, magnons, or charge fluctuations. We describe here the setup developed that allows for the positioning of crystalline samples in an optical cavity of different quality factors, the tuning of the cavity length at cryogenic temperatures, and its optical characterization with a broadband time domain THz spectrometer (0.2–6 THz). We demonstrate the versatility of the setup by studying the vibrational strong coupling in CuGeO3 single crystal at cryogenic temperatures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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