21,365 research outputs found
Mixed state microwave resistivity of cuprate superconductors
No full textWe present a compared experimental investigation of the (a, b) plane vortex-state complex resistivity at 48 GHz in YBa2Cu3O7-delta, SmBa2Cu3O7-delta and Bi2Sr2CaCu2O8+x, In YBa2Cu3O7-delta and SmBa2Cu3O7-delta the field dependence of the response can be consistently by contrast, described by a combination of flux flow and strong pair breaking due to the presence of lines of nodes in the gap. In Bi2Sr2CaCu2O8+x the data might be described by the pair breaking alone. (c) 2005 Elsevier Ltd. All rights reserved
Mixed-state microwave resistivity in RE-BaCuO films
No full textWe present measurements of the microwave complex resistivity at 48 GHz in REBa2Cu3O7-delta thin films (RE = Y, Sm) in moderate magnetic fields (H-mu0 < 0.8 T) and above 60 K. The measured complex resistivity gives valuable information for the study of vortex dynamics. We show that the field dependence of the microwave resistivity has rather different behaviours in YBa2Cu3O7-delta and SmBa2Cu3O7-delta. By applying the conventional model of vortex motion, the data in SmBa2Cu3O7-delta would yield exotic behaviours for the vortex parameters. However, taking into account the enhanced field-induced change in quasiparticle density in a superconductor with lines of nodes in the gap, the vortex part of the response behaves similarly in YBa2Cu3O7-delta and SmBa2Cu3O7-delta
Dynamic regimes in YBCO in applied magnetic field probed by swept frequency microwave measurements
No full textWe report measurements of the microwave resistivity in YBa2Cu3O7-delta (YBCO), in the presence of an applied magnetic field. Measurements are performed as a function of frequency, over a continuum spectrum between 6 and 20 GHz, by means of a Corbino disc geometry. These data allow for a direct identification of different dynamical regimes in the dissipation of YBCO in the presence of an applied magnetic field. While at high temperatures a frequency independent resistivity is observed, at lower temperatures we find a marked frequency dependence. The line in the (H, T) plane at which this change in the dynamical regime is observed is clearly identified and discussed in terms of vortex motion and fluctuational resistivity
Microwave complex resistivity in YBCO films above T-c: effects of fluctuations
No full textWe present measurements of the (a,b) plane complex resistivity at 24 GHz in nearly-optimally doped YBCO films grown by de sputtering with T-c similar or equal to 90 K. The attention is focused above T-c, where we discuss the data in terms of 3D, anisotropic fluctuations. We find that at microwave frequencies simple gaussian fluctuations are unable to describe our data both well above and in the vicinity of the critical temperature. The discrepancy well above T-c is recovered by including a short-wavelength cutoff` in the frequency-dependent fluctuational conductivity. In order to follow the slowing down of the fluctuations at T-c, we treat the region close to T-c including the quartic term of the order parameter in the Ginzburg-Landau functional within the Hartree approximation. We then find excellent agreement with our data from high temperature (T = 1.3 T-c) down to T-c
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
Activation energy in La 0.7 Ca 0.3 MnO 3/YBa 2Cu 3O 7-δ / La 0.7 Ca 0.3 MnO 3 superconducting trilayers
No full textResistivity vs. temperature measurements on La 0.7 Ca 0.3 MnO 3/YBa 2Cu 3O 7-δ /La 0.7 Ca 0.3 MnO 3 (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing the YBCO layer thickness and the absolute U values appear to be reduced with respect to the values reported in literature in the case of YBCO thin films and YBCO/insulating multilayers. Moreover, a logarithmic U vs. H dependence is shown both in the case of thick and thin YBCO layers indicating the formation of a two dimensional vortex lattice. The experimental data are discussed considering the strong influence of the ferromagnetic LCMO on the superconducting YBCO properties which reduces the effective YBCO thickness more than predicted by the conventional theories. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200674.25.Qt Vortex lattices, flux pinning, flux creep, 75.47.Lx Manganites, 74.78.Fk Multilayers, superlattices, heterostructures,
A local field emission study of partially aligned carbon-nanotubes by atomic force microscope probe
No full textAtomic force microscopy (AFM) was used to study the field emission (FE) properties of a dense array of long and vertically quasi-aligned multi-walled carbon nanotubes grown by catalytic chemical vapor deposition on a silicon substrate. The use of nanometric probes enables local field emission measurements to be made allowing the investigation of effects that are not detectable with a conventional parallel plate setup, where the emission current is averaged over a large sample area. The micrometric inter-electrode distance allows one to achieve high electric fields with a modest voltage. These features made us able to characterize field emission for macroscopic electric fields up to 250 V/mu m and attain current densities larger than 10(5) A/cm(2). FE behaviour is analyzed in the framework of the Fowler-Nordheim theory. A field enhancement factor y approximate to 40-50 and a turn-on field Eturn-on similar to 15 V/mu m at an inter-electrode distance of I pm are estimated. Current saturation observed at high voltages in the I-V characteristics is explained in terms of a series resistance of the order of MO. Additional effects, such as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed. (C) 2007 Elsevier Ltd. All rights reserved. RI Giubileo, Filippo/I-2108-201
Metal-insulator transition temperature enhancement in La0.7Ca0.3MnO3 thin films
No full textThe effect of oxygen annealing on the structural and transport properties of La0.7Ca0.3MnO3 thin films deposited on SrTiO3 substrates has been investigated by x-ray diffraction analysis and resistive measurements. The as-grown films are fully tensile strained on the substrates and show a depressed metal-insulator transition temperature T-p= 131 K. As the oxygen content is increased due to longer annealing times, significantly higher T-p are measured, up to 247 K. Correspondingly, an increase of the out-of-plane lattice parameter is observed while the in-plane lattice constants do not change with respect to the as-grown films, which prevents any interpretation of a T-p dependence on the strain. The large increase in T-p is then interpreted in terms of a combined effect of the Mn4+/Mn3+ ratio variation, the change in the carrier density in the a-b planes, and the increase in the hydrostatic strain with the oxygen annealing
I Think I Am Philip K. Dick
No full textFor years, noted writer Laurence A. Rickels often found himself compared to novelist Philip K. Dickthough in fact Rickels had never read any of the science fiction writers work. When he finally read his first Philip K. Dick novel, while researching for his recent book The Devil Notebooks , it prompted a prolonged immersion in Dicks writing as well as a recognition of Rickelss own long-documented intellectual pursuits. The result of this engagement is I Think I Am: Philip K. Dick , a profound thought experiment that charts the wide relevance of the pulp sci-fi author and paranoid visionary. I Think I Am: Philip K. Dick explores the science fiction authors meditations on psychic reality and psychosis, Christian mysticism, Eastern religion, and modern spiritualism. Covering all of Dicks science fiction, Rickels corrects the lack of scholarly interest in the legendary Californian author and, ultimately, makes a compelling case for the philosophical and psychoanalytic significance of Philip K. Dicks popular and influential science fiction.Intro -- Contents -- Introjection -- Part I -- Endopsychic Allegories -- Schreber Guardian -- Belief System Surveillance -- Part II -- Deeper Problems -- Veil of Tears -- Go West -- Dick Manfred -- Timing -- Glimmung -- Part III -- Spiritualism Analogy -- Imitating the Dead -- Indexical Layer -- Ilse -- Hammers and Things -- Crucifictions -- Over There -- Martyrology -- Can't Live, Can't Live -- Lola -- Umwelt, Mitwelt, and Eigenwelt -- Outer Race -- The German Introject -- Part IV -- Materialism, Idealism, and Cybernetics -- Startling Stories -- A Couple of Years -- Android Empathy -- Homunculus and Robot -- ALL OF YOU ARE DEAD. I AM ALIVE. -- Go with the Flow -- Part V -- Room for Thought -- Caduceus -- Jump -- Still -- A Wake -- Spätwerk -- Let the Dead Be -- Play Bally -- Das Hund -- Notes -- BibliographyFor years, noted writer Laurence A. Rickels often found himself compared to novelist Philip K. Dickthough in fact Rickels had never read any of the science fiction writers work. When he finally read his first Philip K. Dick novel, while researching for his recent book The Devil Notebooks , it prompted a prolonged immersion in Dicks writing as well as a recognition of Rickelss own long-documented intellectual pursuits. The result of this engagement is I Think I Am: Philip K. Dick , a profound thought experiment that charts the wide relevance of the pulp sci-fi author and paranoid visionary. I Think I Am: Philip K. Dick explores the science fiction authors meditations on psychic reality and psychosis, Christian mysticism, Eastern religion, and modern spiritualism. Covering all of Dicks science fiction, Rickels corrects the lack of scholarly interest in the legendary Californian author and, ultimately, makes a compelling case for the philosophical and psychoanalytic significance of Philip K. Dicks popular and influential science fiction.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
Microwave fluctuational conductivity in YBaCuO
No full textWe present measurements of the microwave complex conductivity at 23.9 and 48.2 GHz in YBa2Cu3O7-delta films, in the fluctuational region above T-c. With increasing temperature, the fluctuational excess conductivity drops much faster than the well-known calculations within the time-dependent Ginzburg-Landau theory [H. Schmidt, Z. Phys. 216, 336 (1968)]. Approaching the transition temperature, slowing down of the fluctuations is observed. We discuss the results in terms of a modified Gaussian theory for finite-frequency fluctuational conductivity, where renormalization is introduced in order to account for the T --> T-c regime, and a spectral cutoff is inserted in order to discard high-momentum modes. The data are in excellent agreement with the modified theory, when formulated for three-dimensional, anisotropic superconductors, in the whole experimentally accessible temperature range, and for both frequencies
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