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Author (up) Haberkorn, N.; Eomb, M.J.; You, J.S.; Kim, J.; Kim, J.S. openurl 
  Title Critical current densities and flux creep rates in near optimally doped BaFe2- xRuxAs2 (x=0.7) single crystals Type Journal Article
  Year 2016 Publication Solid State Communications Abbreviated Journal  
  Volume 231-232 Issue Pages 26-30  
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  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 747  
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Author (up) Kim, J.; Haberkorn, N.; Gofryk, K.; Graf, M.J.; Ronning, F.; Sefat, A.S.; Movshovich, R.; Civale, L. url  openurl
  Title Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals Type Journal Article
  Year 2015 Publication Solid State Communications Abbreviated Journal Solid State Commun.  
  Volume 201 Issue Pages 20-24  
  Keywords A. Iron arsenide superconductors; B. Upper critical field; C. Magnetic penetration depth; D. Vortex pinning  
  Abstract Abstract

We report the intrinsic superconducting parameters in a heavily overdoped Ba(Fe1−xCox)2As2 (x=0.14) single crystal and their influence in the resulting vortex dynamics. We find a bulk superconducting critical temperature of 9.8 K, magnetic penetration depth λab (0)=660±50 nm, coherence length ξab (0)=6.4±0.2 nm, and the upper critical field anisotropy γT→Tc≈3.7. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. The intrinsic pinning energy plays an important role in the resulting vortex dynamics as compared with similar pinning landscape and comparable intrinsic thermal fluctuations.
 
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  Series Volume Series Issue Edition  
  ISSN 0038-1098 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 724  
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Author (up) Kim, J.; Haberkorn, N.; Nazaretski, E.; Paula, R. de; Tan, T.; Xi, X.X.; Tajima, T.; Movshovich, R.; Civale, L. url  openurl
  Title Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film Type Journal Article
  Year 2015 Publication Solid State Communications Abbreviated Journal Solid State Commun.  
  Volume 204 Issue Pages 56-60  
  Keywords A. Superconducting materials; B. Films; C. Magnetic penetration depth; D. Vortex pinning  
  Abstract We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of λ=50±10 nm at T=4 K is related to a clean Ï€-band. We find a high self-field critical current density Jc, which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the Ï€-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson–Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field.  
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  Series Volume Series Issue Edition  
  ISSN 0038-1098 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 729  
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Author (up) Navarro, H.; Sirena, M.; Kim, J.; Haberkorn, N. url  doi
openurl 
  Title Josephson coupling in high-Tc superconducting junctions using ultra-thin BaTiO3 barriers Type Journal Article
  Year 2020 Publication Materials Science and Engineering: B Abbreviated Journal Mater. Sci. Eng. B  
  Volume 262 Issue Pages 114714  
  Keywords Josephson junctionsHigh-Tc superconductorsThin films  
  Abstract We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa2Cu3O7−δ electrodes and a BaTiO3 barrier with thicknesses between 1 nm and 3 nm. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO3 barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO3. The Josephson coupling temperature reduces as the barrier thicknesses increases. The Josephson energies at 12 K are of ≈ 1.5 mV and ≈ 7.5 mV for BaTiO3 barriers of 1 nm and 2 nm, respectively. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-Tc electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0921-5107 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 858  
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Author (up) Navarro, H.; Sirena, M.; Kim, J.; Haberkorn, N. url  doi
openurl 
  Title Smooth surfaces in very thin GdBa2Cu3O7−δ films for application in superconducting tunnel junctions Type Journal Article
  Year 2015 Publication Physica C: Superconductivity and its Applications Abbreviated Journal Physica C  
  Volume 510 Issue Pages 21-26  
  Keywords Thin films; Superconductivity; Morphology  
  Abstract Abstract

This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa2Cu3O7−δ films grown on (0 0 1) SrTiO3 substrates by DC sputtering. We find that the use of a very thin SrTiO3 buffer layer (≈2 nm) modify the nucleation of GdBa2Cu3O7−δ on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa2Cu3O7−δ films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm2) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry.
 
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  Series Volume Series Issue Edition  
  ISSN 0921-4534 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 726  
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Author (up) Navarro, H.; Yang, I.; Sirena, M.; Kim, J.; Haberkorn, N. url  doi
openurl 
  Title Characterization of the insulator barrier and the superconducting transition temperature in GdBa2Cu3O7−δ/BaTiO3 bilayers for application in tunnel junctions Type Journal Article Article
  Year 2015 Publication Journal of Applied Physics Abbreviated Journal J. Appl. Phys.  
  Volume 118 Issue 4 Pages 045308  
  Keywords  
  Abstract The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO3 tunnel barrier deposited on a 16 nm thick GdBa2Cu3O7−δ thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO3 barrier thickness between 1.6 and 4 nm. The BaTiO3 layers present an energy barrier of ≈1.2 eV and an attenuation length of 0.35–0.5 nm (depending on the applied voltage). The GdBa2Cu3O7−δ electrode is totally covered by a BaTiO3 thickness above 3 nm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4 nm thick BaTiO3 top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO3 thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa2Cu3O7−δ. The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO3 barrier).  
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  ISSN ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number BT @ pedrazp @ Serial 727  
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