<p>In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase that displays a number of exciting phenomena. At low temperatures, vortices form a truly superconducting solid phase which at high temperatures turns into a dissipative vortex liquid. The character of the transition between these two phases depends on the amount and type of disorder present in the system. For weak point disorder the vortex solid-to-liquid transition is a first-order melting. In the presence of strong point disorder the solid is thought to be a vortex-glass and the transition into the liquid is instead of second order. When the disorder is correlated, like twin boundaries or artificially introduced columnar defects, the transition is also second order, but has essentially different properties. In this work, the transition between the solid and liquid phases of the vortex state has been studied by resistive transport measurements in mainly YBa2Cu3O7-[delta](YBCO) single crystals with different types of disorder.</p><p>The vortex-glass transition has been investigated in an extended model for the vortex-liquid resistivity close to the transition that takes into account both the temperature and magnetic field dependence of the transition line. The resistivity of samples with different properties was measured with various contact configurations at several magnetic fields and analyzed within this model. For each sample, attempts were made to scale the transition curves to one curve according to a suitable scaling variable predicted by the model. Good scaling was found in a number of different situations. The influence of increasing anisotropy and angular dependence of the magnetic field in the model were also considered.</p><p>The vortex solid-to-liquid transition was also studied in heavy-ion irradiated YBCO single crystals. The ions create columnar defects in the sample that act as correlated disorder. A magnetic field was applied at a tilt angle with respect to the direction of the columns. At the transition the resistance disappears as a power law with different exponents in the three orthogonal directions considered. This provides evidence for a new type of critical behavior with fully anisotropic critical scaling properties not previously found in any physical system.</p><p>The effect on the vortex solid-to-liquid transition of high magnetic fields applied parallel to the superconducting layers of underdoped YBCO single crystals was also studied. Some novel features were observed: a sharp kink appearing close to Tc at high magnetic fields and a triple dip in the angular dependence of the resistivity close to B||ab in some regions of the phase diagram.</p> / <p>I högtemperatursupraledare består en stor del av det magnetiska fasdiagrammet av en vortexfas som uppvisar ett flertal spännande fenomen. Vid låga temperaturer bildar vortexarna en fast vortexfas utan elektriskt motstånd. Vid högre temperatur övergår denna fas till en dissipativ vortexvätska. Egenskaperna hos denna fasövergång beror på oordningen i form av defekter. Vid svag punktoordning är fasomvandlingen mellan det fasta och flytande vortextillståndet en första ordningens smältövergång. Vid stark punktoordning anses den fasta fasen vara ett vortexglas och övergången till vortexvätskan är istället av andra ordningen. När oordningen är korrelerad, som för tvillinggränser eller artificiellt skapade kolumndefekter, är övergången också av andra ordningen men med väsentligt annorlunda egenskaper. I detta arbete har övergången mellan det fasta och det flytande vortextillståndet studerats med resistiva transportmätningar i framförallt enkristaller av YBa2Cu3O7-[delta] (YBCO) med olika typer av oordning.</p><p>Vortexglasövergången har undersökts i en utvidgad modell för resistansen i vortexvätskan nära fasövergången där hänsyn tas till såväl temperatur- som fältberoendet. Resistansen hos prover med olika egenskaper mättes i varierande magnetfält och i flera kontaktkonfigurationer och analyserades inom denna modell. Övergångskurvorna skalades till en kurva med en skalningsvariabel som givits av modellen. God skalning uppnåddes i flera olika fall. Effekten av ökande anisotropi och vinkelberoendet i modellen undersöktes också.</p><p>Vortexövergången mellan det fasta och det flytande vortextillståndet undersöktes även i enkristaller av YBCO bestrålade med tunga joner. Jonerna skapade kolumndefekter som fungerar som korrelerad oordning. Vinkeln mellan pålagt magnetfält och dessa kolumndefekter varierades. Vid fasövergången avtar resistansen som en potenslag med olika exponenter i de tre undersökta ortogonala riktningarna. Detta ger experimentell belägg för en ny typ av kritiskt beteende med fullständigt anisotropa kritiska skalningsegenskaper.</p><p>Egenskaparna hos på vortexövergången mellan fast och flytande fas vid höga magnetfält parallella med de supraledande lagren hos underdopade YBCO enkristaller undersöktes också. Några nya effekter observerades: en skarp knyck uppstod nära Tc vid höga magnetfält och en tredubbel dipp i den vinkelberoende resistiviteten nära B||ab i några regioner av fasdiagrammet.</p>

No description available.

Die Bestrahlung von tetraedrisch amorphen Kohlenstoff (ta-C) mit schnellen schweren Ionen führt zur Bildung von mikroskopischen elektrisch leitfähigen Ionenspuren mit Durchmessern um 10 nm. Dieses Phänomen ist auf das sp² zu sp³ Hybridisierungsverhältnis des amorphen Kohlenstoffes zurückzuführen. Das einschlagende Ion deponiert eine große Menge Energie innerhalb des Spurvolumens, so dass eine Materialtransformation hin zu höheren sp² Hybridisierung stattfindet. Hierdurch wird die elektrische Leitfähigkeit der Ionenspur stark erhöht. Dieser Effekt kann durch die Zugabe von Verunreinigungen wie Kupfer verstärkt werden. Das Ziel dieser Arbeit ist die umfassende Analyse des elektrischen Verhaltens von ta-C mit besonderen Augenmerk auf die Auswirkungen von Kupferverunreinigungen und Ionenspuren. Der Effekt von Kupferverunreinigungen auf das wichtige Hybridisierungsverhältnis vom amorphen Kohlenstoff wird vermessen. Darüber hinaus wurden alle Proben elektrisch mit makroskopischen Kontakten im Temperaturbeireich von 20 K bis 380 K analysiert. Mikroskopisch wurden einzelne leitfähige Ionenspuren mit Hilfe von atomarer Kraftmikroskopie betrachtet. Die statistische Verteilung der Spureigenschaften in Kohlenstofffilmen mit verschiedenen Kupferkonzentrationen werden verglichen, um die Spurbildung besser zu verstehen. Die normalisierten durchschnittlichen Spurleitfähigkeiten aus mikroskopischen und makroskopischen Messungen werden verglichen. Hierbei kann die Zuverlässigkeit der beiden experimentellen Methoden bewertet werden und mögliche Fehlerquellen ausfindig gemacht werden. Schließlich wird ein Konzept für eine Anwendung unterbrochener Ionenspuren gezeigt.

Le mécanisme menant à des déformations structurales suivant le bombardement d'échantillons de a-Si d'un faisceau d'ions lourds et rapides est sujet de controverses. Nous nous sommes penchés sur l'hypothèse de la formation d'une zone liquide causée par la déposition d'énergie des ions incidents dans le contexte de la théorie du pic thermique. Des échantillons de silicium amorphe furent préparés dans le but d'observer les indices d'une transition de phase l-Si/a-Si suivant la déposition locale d'énergie sur le parcours d'un ion lourd énergétique dans le a-Si. Les échantillons furent implantés d'impuretés de Cu ou d'Ag avant d'être exposés à un faisceau d'ions Ag12+ de 70 MeV. L'utilisation de l'analyse GISAXS est projetée afin d'observer une concentration locale d'impuretés suivant leur ségrégation sur la trace de l'ion. Des masques d'implantation nanométriques d'oxide d'aluminium ont été fabriqués afin d'augmenter la sensibilité de l'analyse GISAXS et une méthode d'alignement de ces masques selon la direction du faisceau fut développée. Le bombardement d'échantillons au travers de ces masques a donné lieu à un réseau de sites d'impacts isolés presque équidistants. / The machanisms underlying structural deformations following swift heavy ion beam a-Si irradiation are subject of debate. We investigated the hypothesis of the presence of a liquid phase in the wake of the energetic ions in the thermal spike framework. a-Si samples were prepared in order to track a transient liquid phase by implanting Cu or Ag on the a-Si surface and exposing the sample to a 70 MeV Ag12+ beam. Cu and Ag are both very sensitive to segregation in Si and are therefore thought to be capable of keeping track of a molten transient state by concentrating on the ion track. Samples are to be investigated with GISAXS. Nanoscale implantation masks were developed from nanoporous alumina membranes in order to impose a pattern on the ion impact sites and thus improve GISAXS sensitivitity. An alignment method is also developed for the positioning of pores parallel to the ion beam direction. A nearly equidistant impact sites pattern was achieved by irradiating fused silica through these implantation masks.

Ultra-Relativistic heavy-ion physics is a promising field of high energy physics connecting two fields: nuclear physics and elementary particle physics. Experimental achievements of the last years have provided an opportunity to study the properties of a new state of matter created in heavy-ion collisions called quark-gluon plasma. The initial state of two colliding nuclei is affected by fluctuations coming from wave- functions of nucleons. These fluctuations lead to the momentum anisotropy of the hadronic matter which is observed by the detectors. The system created in the collision behaves like a fluid, so the initial state is connected to the final state via hydrodynamic evolution. In this thesis we model the evolution with relativistic viscous hydrodynamics. Our results, combined with experimental data, give non trivial constraints on the initial state, thus achieving "reverse engineering" of the heavy-ion collisions. The observable which characterizes the momentum anisotropy is the anisotropic flow vn. We present the first measurements of the first harmonic of the anisotropic flow called directed flow v1 in Pb-Pb collisions at the LHC. We then perform the first viscous hydrodynamic modeling of directed flow and show that it is less sensitive to viscosity than higher harmonics. Comparison of these experimental data with the modeling allows to extract the values of the dipole asymmetry of the initial state, which provides constraints on the models of initial states. A prediction for directed flow v1 in Au-Au collisions is also made for RHIC. We then perform a similar modeling of the second and third harmonics of the anisotropic flow, called respectively elliptic v2 and triangular v3 flow. A combined analysis of the elliptic and triangular flow data compared with viscous hydrodynamic calculations allows us to put constraints on initial ellipticity and triangularity of the system. These constraints are then used as a filter for different models of initial state. At the end of this thesis, we show perspectives in the studies of the initial state which are opened by recent measurements of event-plane correlations which could shed light on the initial state fluctuations.

In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase that displays a number of exciting phenomena. At low temperatures, vortices form a truly superconducting solid phase which at high temperatures turns into a dissipative vortex liquid. The character of the transition between these two phases depends on the amount and type of disorder present in the system. For weak point disorder the vortex solid-to-liquid transition is a first-order melting. In the presence of strong point disorder the solid is thought to be a vortex-glass and the transition into the liquid is instead of second order. When the disorder is correlated, like twin boundaries or artificially introduced columnar defects, the transition is also second order, but has essentially different properties. In this work, the transition between the solid and liquid phases of the vortex state has been studied by resistive transport measurements in mainly YBa2Cu3O7-[delta](YBCO) single crystals with different types of disorder. The vortex-glass transition has been investigated in an extended model for the vortex-liquid resistivity close to the transition that takes into account both the temperature and magnetic field dependence of the transition line. The resistivity of samples with different properties was measured with various contact configurations at several magnetic fields and analyzed within this model. For each sample, attempts were made to scale the transition curves to one curve according to a suitable scaling variable predicted by the model. Good scaling was found in a number of different situations. The influence of increasing anisotropy and angular dependence of the magnetic field in the model were also considered. The vortex solid-to-liquid transition was also studied in heavy-ion irradiated YBCO single crystals. The ions create columnar defects in the sample that act as correlated disorder. A magnetic field was applied at a tilt angle with respect to the direction of the columns. At the transition the resistance disappears as a power law with different exponents in the three orthogonal directions considered. This provides evidence for a new type of critical behavior with fully anisotropic critical scaling properties not previously found in any physical system. The effect on the vortex solid-to-liquid transition of high magnetic fields applied parallel to the superconducting layers of underdoped YBCO single crystals was also studied. Some novel features were observed: a sharp kink appearing close to Tc at high magnetic fields and a triple dip in the angular dependence of the resistivity close to B||ab in some regions of the phase diagram. / I högtemperatursupraledare består en stor del av det magnetiska fasdiagrammet av en vortexfas som uppvisar ett flertal spännande fenomen. Vid låga temperaturer bildar vortexarna en fast vortexfas utan elektriskt motstånd. Vid högre temperatur övergår denna fas till en dissipativ vortexvätska. Egenskaperna hos denna fasövergång beror på oordningen i form av defekter. Vid svag punktoordning är fasomvandlingen mellan det fasta och flytande vortextillståndet en första ordningens smältövergång. Vid stark punktoordning anses den fasta fasen vara ett vortexglas och övergången till vortexvätskan är istället av andra ordningen. När oordningen är korrelerad, som för tvillinggränser eller artificiellt skapade kolumndefekter, är övergången också av andra ordningen men med väsentligt annorlunda egenskaper. I detta arbete har övergången mellan det fasta och det flytande vortextillståndet studerats med resistiva transportmätningar i framförallt enkristaller av YBa2Cu3O7-[delta] (YBCO) med olika typer av oordning. Vortexglasövergången har undersökts i en utvidgad modell för resistansen i vortexvätskan nära fasövergången där hänsyn tas till såväl temperatur- som fältberoendet. Resistansen hos prover med olika egenskaper mättes i varierande magnetfält och i flera kontaktkonfigurationer och analyserades inom denna modell. Övergångskurvorna skalades till en kurva med en skalningsvariabel som givits av modellen. God skalning uppnåddes i flera olika fall. Effekten av ökande anisotropi och vinkelberoendet i modellen undersöktes också. Vortexövergången mellan det fasta och det flytande vortextillståndet undersöktes även i enkristaller av YBCO bestrålade med tunga joner. Jonerna skapade kolumndefekter som fungerar som korrelerad oordning. Vinkeln mellan pålagt magnetfält och dessa kolumndefekter varierades. Vid fasövergången avtar resistansen som en potenslag med olika exponenter i de tre undersökta ortogonala riktningarna. Detta ger experimentell belägg för en ny typ av kritiskt beteende med fullständigt anisotropa kritiska skalningsegenskaper. Egenskaparna hos på vortexövergången mellan fast och flytande fas vid höga magnetfält parallella med de supraledande lagren hos underdopade YBCO enkristaller undersöktes också. Några nya effekter observerades: en skarp knyck uppstod nära Tc vid höga magnetfält och en tredubbel dipp i den vinkelberoende resistiviteten nära B||ab i några regioner av fasdiagrammet. / QC 20110125

No description available.

Des calculs de type modèle en couches ont été réalisés dans un espace de valence 1¯hω complet pour les noyaux de la couche sd. Ces calculs ont permis pour la première fois de prédire la durée de vie des états de parité positive et négative des noyaux riches en neutrons de la couche sd. Les durées de vie prédites (1 - 100 ps) sont mesurables par la méthode de décalage Doppler différentiel.Le démonstrateur du détecteur γ européen de nouvelle génération, AGATA, en coïncidence avec le spectromètre magnétique PRISMA du LNL (Italie) et le plunger de l’Université de Cologne ont été utilisés pour mesurer les durées de vie des états excités dans 32,33Si et 35,36S. Les structures plus complexes, à n¯hω ont également été étudiées dans le 28Si. Ce dernier est un noyau important pour comprendre la compétition entre les structures de type champ moyen et les structures en agrégats. La réaction résonante de capture radiative d’ions lourds-légers 12C+16O a été réalisée à des énergies sous-coulombiennes. La décroissance γ complète depuis les résonances peuplées par laréaction jusqu’au niveau fondamental de 28Si a été mesurée pour la première fois à ces énergies et montre une forte alimentation d’états intermédiaires autour de 10 MeV. Les comparaisons avec des études de captures radiatives au-dessus de la barrière de Coulomb ont été effectuées et les résultats ont été interprétés en termes de l’alimentation favorisée d’états à isospin T = 1 dans le noyau autoconjugué 28Si. / New large-scale shell-model calculations with full 1¯hω valence space for the sd-nuclei has been used for the first time to predict lifetimes of positive and negative parity states in neutron rich Si isotopes. The predicted lifetimes (1 - 100 ps) fall in the range of the differential Doppler shift method. Using the demonstrator of the European next generation γ-ray array, AGATA, in coincidence with the large acceptance PRISMA magnetic spectrometer from LNL (Legnaro) and the differential plunger of the University of Cologne, lifetimes of excited states in 32,33Si and 35,36S nuclei were measured. In a second step, the n¯hω structure in the stable 28Si nucleus was also studied. 28Si is an important nucleus to understand the competition between mean-field and cluster structures. It displays a wealth of structures in terms of deformation and clustering. Light heavy-ion resonant radiative capture 12C+16O has been performed at energies below the Coulomb barrier. The measured γ-spectra indicate for the first time at these energies that the strongest part of the resonance decay proceeds though intermediate states around 10 MeV. Comparisons with previous radiative capture studies above the Coulomb barrier have been performed and the results have been interpreted in terms of a favoured feeding of T = 1 states in the 28Si self-conjugate nucleus.

Orientador: Jun Takahashi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T10:21:35Z (GMT). No. of bitstreams: 1 Vasconcelos_GeraldoMagelaSeverino_M.pdf: 4363414 bytes, checksum: 50c5bd667b62ccab57088d6b77e1ec81 (MD5) Previous issue date: 2008 / Resumo: As colisões de íons pesados em energias relativísticas permitem estudar o comportamento da matéria nuclear em condições extremas de temperatura e alta densidade de energia. Nessas condições, espera-se uma transição de fase da matéria onde seria formado um estado de quarks e glúons livres, conhecido como Plasma de Quarks e Glúons (QGP). Com o objetivo de estudar a formação deste novo estado e suas características, o experimento STAR, situado no Laboratório Nacional de Brookhaven, Nova Iorque, mede vários canais observáveis das colisões de íons pesados. Uma das marcas da formação do QGP é o aumento da produção de estranheza. O objetivo deste trabalho foi estudar a produção dos bárions multi-estranhos X e W produzidos nas colisões de Cu+Cu com energia de 62,4 GeV=A no referencial do centro de massa (CM), medidos no experimento STAR. Foram obtidos os espectros de momento transverso dessas partículas e a partir deles foi extraída a abundância de produção por unidade de rapidez na região de rapidez central (dN=dy)y=0. A produção desses bárions foi comparada com os resultados de um outro sistema (Au+Au) na mesma energia para estudar a dependência da produção de estranheza em função do tamanho do sistema formado. Os resultados mostraram que a produção de estranheza cresce com o tamanho do sistema, e que este aumento é ligeiramente maior para o sistema de Cu+Cu do que Au+Au. Os resultados deste trabalho são inéditos e complementam um estudo sistemático da produção de estranheza. Também são importantes para a compreensão dos mecanismos de produção de estranheza em diferentes energias / Abstract: Relativistic heavy-ion collisions allow us to study the behavior of nuclear matter at extreme conditions of temperature and energy density. In these conditions, we expect a phase transition of matter where a free state of quarks and gluons would be formed, and that is known as Quark-Gluon Plasma (QGP). With the aim to study this new state of matter and its features, the STAR experiment was built at BNL (Brookhaven National Laboratory), New York. The STAR experiment measures many observables of heavy-ion collisions and in particular, the strangeness enhancement in QGP is of special interest. The aim of this work was the study of multi-strange baryon production, X and W , at collisions of Cu+Cu in the center of mass energy of 62.4 GeV=A measured at the STAR experiment. Transverse momentum spectra and integrated yields for X and W at mid-rapidity are presented in this work. We also compared Cu+Cu and Au+Au systems in order to study the dependence of strange particle production with the system size. The results showed that strangeness production enhances with the system size, and strange baryons yields in Cu+Cu are slightly larger than Au+Au for the same energy. The new results obtained here complement a systematic study of strangeness production in heavy ion collisions and are important to understand the strangeness particle production mechanism in different energies / Mestrado / Física Nuclear / Mestre em Física

Orientador: Jun Takahashi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-23T16:49:52Z (GMT). No. of bitstreams: 1 Souza_RafaelDerradide_D.pdf: 5902855 bytes, checksum: ef026256d77f665d1d9d346c08ad7ec8 (MD5) Previous issue date: 2013 / Resumo: Nas colisões nucleares relativísticas, devido ao comportamento coletivo do sistema, é esperado que a anisotropia espacial inicial da região de uperposição entre os núcleos incidentes seja convertida em uma anisotropia final na distribuição de momento das partículas produzidas. Em particular, o coeficiente de fluxo elíptico, dado pelo segundo harmônico (v2) da decomposição de Fourier da distribuição azimutal das partículas finais produzidas, é um observável sensível à anisotropia geométrica inicial. Neste trabalho, estudamos o comportamento do coeficiente v2 obtido a partir de eventos gerados com o código de evolução hidrodinâmica NeXSPheRIO simulando colisões Au+Au a (SNN)1/2 = 200 GeV. O NeXSPheRIO permite o controle da condição inicial, da evolução hidrodinâmica e gera as partículas finais como em um evento real. Portanto, foi possível aplicar as mesmas técnicas de análise de dados utilizadas experimentalmente. Estudamos os efeitos de flutuações na condição inicial no observável v2 e testamos alguns observáveis experimentais propostos que seriam sensíveis a estas flutuações. Como os observáveis também são sensíveis a outros tipos de correlações, geralmente chamadas de non-flow, e considerando que a maior contribuição pode vir de jatos de partículas gerados nessas colisões, estudamos os efeitos de jatos nesses observáveis. Construímos um modelo simplificado de duas componentes a partir da superposição de eventos NeXSPheRIO, com eventos de colisões p+p produzidos pelo gerador de eventos Pythia. Resultados deste modelo descrevem melhor a dependência de v2 com o momento transversal quando comparados com dados experimentais. Determinamos também que, ao contrário do que se esperava, os observáveis sensíveis à flutuação na condição inicial são pouco afetados pela inclusão dos jatos. Este resultado sugere que os efeitos de non-flow, como considerados aqui, são desprezíveis nas medidas de flutuações de v2, indicando que os resultados obtidos pelos experimentos sejam dominados pelas flutuações da condição inicial / Abstract: Due to the collective behavior of the system created in relativistic nuclear collisions, it is expected that the initial spatial anisotropy of the overlap region between the two incoming nuclei converts into an anisotropy of the momentum distribution of the outgoing particles. In particular, the elliptic flow coefficient, which is given by the second harmonic (v2) of the Fourier decomposition of the final particle azimuthal distribution, is an observable sensitive to the initial geometric anisotropy. In this work, we studied the behavior of the elliptic flow coefficient obtained from events generated using the hydrodynamic-based code NeXSPheRIO for Au+Au collisions at (SNN)1/2= 200 GeV. The NeXSPheRIO code allows the control of the initial condition, the hydrodynamic evolution and produces the outgoing particles just like in a real event. Therefore, it was possible to apply the same data analysis techniques used experimentally. We studied the effects of initial condition fluctuations on flow observables and tested some experimental observables thought to be sensitive to the fluctuations. Since these observables are also sensitive to other types of correlations, usually referred to as non-flow, and considering that the major contribution to them may come from jets of particles generated in the collision, we also studied the effects of jets on these observables. A simplified two-component model was built by superimposing events produced with the NeXSPheRIO code and p+p collision events produced with the Pythia event generator. Results from our model present a better description of the ?2 dependence with transverse momentum when compared to experimental data. Also, opposite to what was expected, the observables sensitive to the fluctuations are not much sensitive to the inclusion of jets. This result may suggest that the contribution of non-flow, as considered here, is negligible in the observed flow fluctuations measurement, which indicates that the values observed in the experiments are mainly dominated by fluctuations from the initial condition / Doutorado / Física / Doutor em Ciências