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Author |
Maiorov, B.; Nieva, G.; Osquiguil, E. |
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Title |
First-order phase transition of the vortex lattice in twinned YBa2Cu3O7 single crystals in tilted magnetic fields |
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Journal Article |
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Year |
2000 |
Publication |
Physical Review B – Condensed Matter and Materials Physics |
Abbreviated Journal |
Phys. Rev. B Condens. Matter Mater. Phys. |
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61 |
Issue |
18 |
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12427-12432 |
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We present an exhaustive analysis of transport measurements performed in twinned YBa2Cu3O7 single crystals which establishes that the vortex solid-liquid transition is first order when the magnetic field H is applied at an angle ? away from the direction of the twin planes. We show that the resistive transitions are hysteretic and the V-I curves are nonlinear, displaying a characteristic S shape at the melting line Hm(T), which scales as ?(?)Hm(T,?), where ?(?) is the anisotropy factor. These features are gradually lost when the critical point H*(?) is approached. Above H*(?) the V-I characteristics show a linear response in the experimentally accessible V-I window, and the transition becomes reversible. Finally we show that the first-order phase transition takes place between a highly correlated vortex liquid in the field direction and a solid state of unknown symmetry. As a consequence, our data support the scenario for a vortex-line melting in twinned YBa2Cu3O7 crystals in contrast to a vortex sublimation as recently suggested for untwinned La2-xSrxCuO4, YBa2Cu3O7 and Bi2Sr2CaCu2O8 [T. Sasagawa et al., Phys. Rev. Lett. 80, 4297 (1998)]. |
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01631829 (ISSN) |
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Cited By (since 1996): 5; Export Date: 17 April 2009; Source: Scopus; CODEN: PRBMD; Language of Original Document: English; Correspondence Address: Maiorov, B.; Centro At |
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BT @ osquigui @ |
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372 |
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Fainstein, A.; Maiorov, B.; Guimpel, J.; Nieva, G.; Osquiguil, E. |
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Title |
Annealing disorder and photoinduced order of oxygen chains in detwinned YBa2Cu3O6.65 single crystals probed by Raman scattering |
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Journal Article |
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Year |
2000 |
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Physical Review B – Condensed Matter and Materials Physics |
Abbreviated Journal |
Phys. Rev. B Condens. Matter Mater. Phys. |
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61 |
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6 |
Pages |
4298-4304 |
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Raman scattering in detwinned YBa2Cu3O6.65 single crystals is studied as a function of photoexcitation and annealing. Copper-oxygen chain-related forbidden Raman bands that are known to strongly bleach with illumination at low temperatures, increase their intensity with chain fragmentation induced by annealing at high temperature. This contrasting behavior proves the conjunction of short Cu-O fragments into longer chains on photoexcitation. We interpret the Raman modes as due to vibrations at the end of CuO chain fragments and Cu-O-Cu monomers, and use their evolution with illumination and annealing as anisotropic sensitive markers of oxygen reordering processes. The identification of the “forbidden” Raman bands is discussed in the context of our results and recent literature in the subject. We also present absorption measurements performed on GdBa2Cu3Ox thin films with varying oxygen content. These experiments show that the 2.2-eV absorption and the chain-related Raman peaks have different dependencies with oxygen content and illumination, ruling out an explanation that suggests that the Raman intensity reduction of these modes is due to a photobleaching of intermediate defect states. These results highlight the potentialities of Raman scattering for oxygen dynamics studies and demonstrate the presence of photoinduced oxygen ordering in these high-Tc superconductor compounds. |
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Cited By (since 1996): 18; Export Date: 17 April 2009; Source: Scopus; CODEN: PRBMD; Language of Original Document: English; Correspondence Address: Fainstein, A.; Centro At |
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BT @ osquigui @ |
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374 |
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Luzuriaga, J. |
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Title |
Sphere on a vibrating reed for measurements of turbulence in superfluid helium |
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2000 |
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Journal of Alloys and Compounds |
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J Alloys Compd |
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265-268 |
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Cantilever beams; Computational methods; Laminar flow; Oscillators (electronic); Phase transitions; Turbulent flow; Vibrations (mechanical); Oscillating spheres; Spherical geometries; Vibrating reeds; Superfluid helium |
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A modification of the vibrating reed, in which a massive sphere is made to oscillate at the end of a cantilevered beam, has been used for measurements in superfluid helium. The apparatus operates in the same way as a conventional vibrating reed with capacitive detection and drive. However, when operating submerged in the liquid, the frequency changes give information on the superfluid fraction, and the dissipation can be used to obtain information on the change of liquid flow, from laminar to turbulent. The spherical geometry allows an exact calculation of all parameters in the laminar regime, so departures due to the turbulence can be better quantified. The method has been found to work well in practice, and some measurements on the turbulent regime in the superfluid are presented. |
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Elsevier Sequoia SA |
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Buenos Aires, Argent |
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12th International Conference on Internal Friction and Ultrasonic Attenuation in Solids (ICIFUAS-12) |
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Series Volume |
310 |
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1-2 |
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09258388 (ISSN) |
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Conference code: 57483; Export Date: 28 April 2009; Source: Scopus; CODEN: JALCE; doi: 10.1016/S0925-8388(00)00962-2; Language of Original Document: English; Correspondence Address: Luzuriaga, Javier; Centro Atomico Bariloche Bariloche, Argentina; Sponsors: ABDUS SALAM International Centre for Theoretical Physics; Centre for Industrial Research (CINI); Comision Nacional de Actividades Espaciales (CONAE) |
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BT @ luzuriag @ |
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478 |
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Marconi, V. I.; Candia, S.; Balenzuela, P.; Pastoriza, H.; Domínguez, D.; Martinoli, P. |
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Title |
Orientational pinning and transverse voltage: Simulations and experiments in square Josephson junction arrays |
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2000 |
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Phys. Rev. B |
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62 |
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6 |
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4096-4104 |
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We study the dependence of the transport properties of square Josephson Junctions arrays with the direction of the applied dc current, both experimentally and numerically. We present computational simulations of current-voltage curves at finite temperatures for a single vortex in an array of $L\times L$ junctions ($Ha^2/?_0=f=1/L^2$), and experimental measurements in $100\times1000$ arrays under a low magnetic field corresponding to $f\approx0.02$. We find that the transverse voltage vanishes only in the directions of maximum symmetry of the square lattice: the [10] and [01] direction (parallel bias) and the [11] direction (diagonal bias). For orientations different than the symmetry directions, we find a finite transverse voltage which depends strongly on the angle φ of the current. We find that vortex motion is pinned in the [10] direction ($?=0$), meaning that the voltage response is insensitive to small changes in the orientation of the current near $?=0$. We call this phenomenon orientational pinning. This leads to a finite transverse critical current for a bias at $?=0$ and to a transverse voltage for a bias at $?\not=0$. On the other hand, for diagonal bias in the [11] direction the behavior is highly unstable against small variations of φ, leading to a rapid change from zero transverse voltage to a large transverse voltage within a few degrees. This last behavior is in good agreement with our measurements in arrays with a quasi-diagonal current drive. |
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BT @ hernan @ marconi00 |
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26 |
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Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. |
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Title |
Repetition of the disordered pattern in successive solidifications of vortex matter observed by Bitter decoration |
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Journal Article |
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2000 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
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62 |
Issue |
1 |
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678-681 |
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Repeated images of the vortex structure in YBa2Cu3O7-delta Single crystals have been obtained, using the Bitter technique. By removing the iron dots between each decoration experiment, it is possible to image the vortices in different cooldown runs done under the same field and temperature conditions. The images show that these different realizations of a disordered vortex state found in twinned crystals are very similar at long range and differ only in small-scale detail. This is unusual behavior in glassy systems, where expectations are that successive configurations will differ over many scales. In contrast, ordered vortex crystals in clean samples can form with different orientations in different runs, therefore differing at long ranges. Double-sided decorations have been performed in twinned samples, and the correlation between images in both sides of the sample is similar in magnitude but slightly different qualitatively than that found in successive decorations. |
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0163-1829 |
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ISI:000088037000106 |
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BT @ hernan @ |
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225 |
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Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. |
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Title |
Interplay between pinning energy and vortex interaction in YBa2Cu3O7-delta with oriented twin boundaries in tilted magnetic fields: Bitter decoration and tilt-modulus measurements |
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Journal Article |
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2000 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
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Volume |
62 |
Issue |
5 |
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3534-3541 |
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We have performed Bitter decoration and ac susceptibility measurements in single-crystal YBa2Cu3O7-delta with oriented twin boundaries. The twin boundaries (TB's) pin vortices over approximately 65% of the sample. The pinned areas are unevenly distributed and some relatively large TB-free regions are present. The Bitter decorations were performed in a 52 Oe de magnetic field rotated off the c axis so that the plane defined by the field direction and the c axis is perpendicular to the TB's. Several decorations were performed in the same sample. Additional dynamical information was obtained from ac susceptibility measurements. Results show that for small tilts the vortices remain locked to the c-axis direction, for angles greater than 12 degrees they form a staircase pattern, and in this case pinning by the twin boundaries remains effective up to 75 degrees. We observe vortex chains in twin-free-zones of the sample for tilted fields at 65 degrees and 40 degrees. Due to our particular experimental arrangement, in the twinned regions the interplay of the potentials giving rise to the chains and the pinning potential produces a structure with a disordered square symmetry. The data allow us to estimate the dominant energy of the vortex system for some inclinations of the applied magnetic field. |
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0163-1829 |
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ISI:000088714200086 |
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BT @ hernan @ |
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224 |
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Roa Rojas, J.; Jurelo, A.R.; Menegotto Costa, R.; Mendonca Ferreira, L.; Pureur, P.; Orlando, M.T.D.; Prieto, P.; Nieva, G. |
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Fluctuation conductivity and the dynamical universality class of the superconducting transition in the high-Tc cuprates |
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2000 |
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Physica C: Superconductivity |
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Physica C |
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341-348 |
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3 |
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1911-1912 |
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Systematic measurements of the fluctuation conductivity in several high-temperature superconducting cuprates show the occurrence of a genuine critical regime. The conductivity exponent is consistent with the predictions of the 3D-XY universality class and yields a dynamical critical exponent z = 1.5. |
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0921-4534 |
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ISI:000165855900185 |
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BT @ hernan @ |
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223 |
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Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. |
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Reproducibility of the disordered vortex structure in twinned single crystals of YBCO |
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Journal Article |
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2000 |
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Physica C |
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Physica C |
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341 |
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1087-1088 |
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Bitter decorations of the vortices in twinned single crystal YBCO have been obtained to study the disordered structure formed on successive cooldowns of the sample under the same conditions of field and temperature. Between succesive decorations, the iron dots could be removed completely, giving a surface clean enough for further decoration. It was found that successive realizations of the disordered vortex state were very similar at long range, and differed mostly on short scales, compared to the average vortex separation. We have quantified the correlation between successive structures, and double sided decorations have been also performed to compare with the extent of spatial correlation in the applied field direction. The coincidence of the position of the vortices in successive realizations of the structure, is unexpected, and indicates an unusual behavior for a glassy system. Our technique makes it possible to image the position of the vortices in detail and repeatedly, providing us with a model amorphous system in which to study the reproducibility of the disordered structure. |
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0921-4534 |
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ISI:000165855700143 |
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BT @ hernan @ |
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220 |
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André, M-O.; Polichetti, M.; Pastoriza, H.; Kes, P. H. |
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Vortex dynamics in 2H-NbSe$_2$ containing a periodic channel structure |
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2000 |
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Physica C |
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338 |
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179-188 |
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We have measured the resistivity and magnetic AC susceptibility of 2H-NbSe single crystals containing alternating 2 stripes of irradiated and non-irradiated regions of columnar defects created by heavy-ion bombardment. Without applied magnetic field, the sample undergoes a double-step transition into the superconducting state, each step corresponding to the transitions in the irradiated and non-irradiated regions, respectively. For fields smaller than half of the matching field and upon increasing the temperature, the onset of flux motion in the non-irradiated channels occurs, when the applied stress due to the electrical current equals the shear stress at the channel edges, while depinning in the irradiated stripes occurs at higher temperature. The weak amplitude dependence of the shear process suggests that it takes place at the melting transition. We observed only a single-step transition at DC magnetic fields larger than half the matching field, because pinning by the columnar defects in the irradiated stripes is much less effective, and consequently the shear stress at the channel edges is strongly reduced. The comparison between the shear stress deduced from I curves and the theoretical value $?max = AC66$ yields a value for the constant Α, which is in good agreement with theoretical predictions. |
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BT @ hernan @ andre99 |
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Herbsommer, Juan A. |
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Dinámica y estática de vórtices en superconductores de alta temperatura crítica con defectos correlacionados |
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2000 |
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Instituto Balseiro |
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Ph.D. thesis |
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