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Author Jaime, M.; Movshovich, R.; Stewart, G.R.; Beyermann, W.P.; Berisso, M.G.; Hundley, M.F.; Canfield, P.C.; Sarrao, J.L. openurl 
  Title Closing the spin gap in the Kondo insulator Ce3Bi4Pt3 at high magnetic fields Type Journal Article
  Year 2000 Publication Nature Abbreviated Journal  
  Volume (down) 405 Issue 6783 Pages 160-163  
  Keywords  
  Abstract Kondo insulator materials(1)-such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3 and SmB6-are 3d, 4f and 5f intermetallic compounds that have attracted considerable interest in recent years(2-5). At high temperatures, they behave like metals. But as temperature is reduced, an energy gap opens in the conduction band at the Fermi energy and the materials become insulating. This contrasts with other f-electron compounds, which are metallic at all temperatures. The formation of the gap in Kondo insulators has been proposed to be a consequence of hybridization between the conduction band and the f-electron levels(6,7), giving a 'spin' gap. If this is indeed the case, metallic behaviour should be recovered when the gap is closed by changing external parameters, such as magnetic field or pressure. Some experimental evidence suggests that the gap can be closed in SmB6 (refs 5, 8) and YbB12 (ref. 9). Here we present specific-heat measurements of Ce3Bi4Pt3 in d.c. and pulsed magnetic fields up to 60 tesla. Numerical results and the analysis of our data using the Coqblin-Schrieffer model demonstrate unambiguously a field-induced insulator-to-metal transition.  
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  Series Volume Series Issue Edition  
  ISSN 0028-0836 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000087080100043 Approved no  
  Call Number BT @ hernan @ Serial 300  
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Author Sirena, M.; Steren, L.; Guimpel, J. openurl 
  Title Thickness dependence of the properties of La0.6Sr0.4MnO3 thin films Type Journal Article
  Year 2000 Publication Thin Solid Films Abbreviated Journal  
  Volume (down) 373 Issue 1-2 Pages 102-106  
  Keywords  
  Abstract We have studied the thickness dependence of the transport and magnetic properties of strongly textured La0.6Sr0.4MnO3 thin films grown on MgO and SrTiO3, for thickness between 5 and 500 nm. While the resistivity and the magnetoresistance are strongly affected, the magnetization is only moderately changed. The effect on the metal-insulator transition, the low field magnetoresistance and carrier localization is dependent on the substrate, evidencing the effect of the induced defects and strains. (C) 2000 Elsevier Science S.A. All rights reserved.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0040-6090 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000090045900024 Approved no  
  Call Number BT @ hernan @ Serial 176  
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Author Silhanek, K.; Guimpel, J.; Civale, L.; Lanza, H.; Levy, P. openurl 
  Title Thickness effects on the pinning by columnar defects Type Journal Article
  Year 2000 Publication PHYSICA C Abbreviated Journal  
  Volume (down) 341 Issue Pages 1217-1218  
  Keywords  
  Abstract We compare the angular dependence of the pinning of equivalent columnar defects in GdBa2Cu2O7 thin films and a thicker YBa2Cu3O7 single crystal. The tracks' related enhancement of the critical currents is much smaller for the case of the thin films. We interpret this thickness dependence as resulting from a competition between the pinning of the correlated structures, related to total sample thickness, and surface boundary conditions, which force the vortices to depin from the columnar defects near the sample surface.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700208 Approved no  
  Call Number BT @ hernan @ Serial 175  
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Author Herbsommer, J.A.; Nieva, G.; Luzuriaga, J. doi  openurl
  Title Reproducibility of the disordered vortex structure in twinned single crystals of YBCO Type Journal Article
  Year 2000 Publication Physica C Abbreviated Journal Physica C  
  Volume (down) 341 Issue Pages 1087-1088  
  Keywords  
  Abstract 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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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700143 Approved no  
  Call Number BT @ hernan @ Serial 220  
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Author Correa, V.F.; Herbsommer, J.A.; Kaul, E.E.; de la Cruz, F.; Nieva, G. openurl 
  Title Onset of the 0-dimensional vortex pinning behavior in the optimally doped and overdoped Bi2Sr2CaCu2O8+delta system Type Journal Article
  Year 2000 Publication PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Abbreviated Journal  
  Volume (down) 341 Issue Pages 1285-1286  
  Keywords  
  Abstract We report results of transverse AC magnetic permeability in the linear regime and DC magnetization loops for optimally doped and oxygen overdoped samples of Bi2Sr2CaCu2O8+delta The data cover the low temperature (T < 25K) and low held (H-a < 1000 Oe) region of the magnetic (H-a-T) phase diagram. In optimally doped as well as in overdoped samples a crossover to a O-dimensional pinning regime (Larkin length, L-C(C), shorter than the inter-plane CuO2 distance) is observed at a characteristic temperature Too for all investigated fields. The order-disorder transition, identified by the second peak in magnetization and a non monotonous field dependence of the AC penetration depth, is quenched below T-0D.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700242 Approved no  
  Call Number BT @ hernan @ Serial 221  
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Author Kaul, E.E.; Nieva, G. openurl 
  Title Oxygen doping effects on the magnetization of Bi2Sr2CaCu2O8+delta single crystalline system in the mixed state Type Journal Article
  Year 2000 Publication PHYSICA C Abbreviated Journal  
  Volume (down) 341 Issue Pages 1343-1344  
  Keywords  
  Abstract We present a systematic study of the oxygen overdoping effects on the de magnetization loops of Bi2Sr2CaCu2O8+delta single crystalline samples. The overdoping is produced by high oxygen pressure (from 1 to 190 bar) annealing at 500 degreesC. The super conducting critical temperature and the c-axis lattice parameter are used to identify the oxygen content of the samples. The dc magnetization loop measurements are performed with the applied magnetic field parallel to the c-axis of the crystals. The characteristic second peak in the magnetization is present far all the investigated oxygen contents. We show that the position of this second peak and the irreversibility field increase monotonically as a function of oxygen doping.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855700271 Approved no  
  Call Number BT @ hernan @ Serial 222  
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Author Roa Rojas, J.; Jurelo, A.R.; Menegotto Costa, R.; Mendonca Ferreira, L.; Pureur, P.; Orlando, M.T.D.; Prieto, P.; Nieva, G. doi  openurl
  Title Fluctuation conductivity and the dynamical universality class of the superconducting transition in the high-Tc cuprates Type Journal Article
  Year 2000 Publication Physica C: Superconductivity Abbreviated Journal Physica C  
  Volume (down) 341-348 Issue 3 Pages 1911-1912  
  Keywords  
  Abstract 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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  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000165855900185 Approved no  
  Call Number BT @ hernan @ Serial 223  
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Author André, M-O.; Polichetti, M.; Pastoriza, H.; Kes, P. H. doi  openurl
  Title Vortex dynamics in 2H-NbSe$_2$ containing a periodic channel structure Type Journal Article
  Year 2000 Publication Physica C Abbreviated Journal  
  Volume (down) 338 Issue Pages 179-188  
  Keywords  
  Abstract 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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  Notes Approved no  
  Call Number BT @ hernan @ andre99 Serial 2  
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Author Pedrazzini, P.; Schmerber, G.; Berisso, M.G.; Kappler, J.P.; Sereni, J.G. openurl 
  Title Magnetic and superconducting properties of A(7)B(3) compounds (A = Th or La and B=Ni, Co, Fe or Pd, Rh, Ru) Type Journal Article
  Year 2000 Publication PHYSICA C Abbreviated Journal  
  Volume (down) 336 Issue 1-2 Pages 10-18  
  Keywords  
  Abstract High-temperature magnetization, low temperature specific heat, and ac-susceptibility measurements on Th7X3 (X = Ni, Co, and Fe) and La(7)Z(3) (Z = Pd, Rh, and Ru) superconductors are presented. The magnetic behaviour of the Th7X3 group has the characteristics of Pauli paramagnets. The La(7)Z(3) group also shows Pauli paramagnetism for Z = Pd and Ru, and signs of spin fluctuations for La7Rh3. Specific heat (C-p) measurements indicate a conventional BCS behaviour for La7Pd3 and La7Rh3, like that of the previously measured Th7X3 superconductors. in the case of La7Ru3, the reduced specific heat jump at the transition, the anomalous temperature dependence of C-p under magnetic field and a large upper critical field slope are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000088047500002 Approved no  
  Call Number BT @ hernan @ Serial 78  
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Author Pastoriza, H.; Candia, S.; Nieva, G. openurl 
  Title Anisotropic vortex dynamics in twined YBaCuO single crystals Type Journal Article
  Year 2000 Publication Physica B Abbreviated Journal  
  Volume (down) 284-288 Issue 2 Pages 763-764  
  Keywords  
  Abstract Rotating continuously the applied vortex force and measuring the vortex velocity vector, we were able to directly determine the role of twin boundaries in the vortex dynamics in YBa$2$Cu$3Ο_7$ single crystals with unidirectional twins. We show the different effect of these correlated pinning defects into the various vortex phases. In the entangled vortex liquid state, we observe a linear response but with an anisotropic viscosity. On the other hand, an anomalous guided motion by twin planes is found in the vortex solid.  
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  Notes Approved no  
  Call Number BT @ hernan @ pastoriza00 Serial 39  
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