Saicharan Aswartham

Publications (4)0 Total impact

• Article: Intrinsic pinning and the critical current scaling of clean epitaxial Fe(Se,Te) thin films

  Kazumasa Iida, Jens Haenisch, Elke Reich, Fritz Kurth, Ruben Huehne, Ludwig Schultz, Bernhard Holzapfel, Ataru Ichinose, Masafumi Hanawa, Ichiro Tsukada, Michael Schulze, Saicharan Aswartham, Sabine Wurmehl, Bernd Buechner
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  ABSTRACT: We report on the transport properties of clean, epitaxial Fe(Se,Te) thin films prepared on Fe-buffered MgO (001) single crystalline substrates by pulsed laser deposition. Near Tc a steep slope of the upper critical field for H||ab was observed (74.1 T/K), leading to a very short out-of-plane coherence length, \xi c, of 0.2 nm, yielding 2\xi c(0) approximately 0.4 nm. This value is shorter than the interlayer distance (0.605 nm) between Fe-Se(Te) planes, indicative of modulation of the superconducting order parameter along the c-axis. An inverse correlation between the power law exponent N of the electric field-current density (E-J) curve and the critical current density, Jc, has been observed at 4 K, when the orientation of H was close to the ab-plane. These results prove the presence of intrinsic pinning in Fe(Se,Te). A successful scaling of the angular dependent Jc and the corresponding exponent N can be realized by the anisotropic Ginzburg Landau approach with appropriate \Gamma values 2~3.5. The temperature dependence of \Gamma behaves almost identically to that of the penetration depth anisotropy.
  03/2013;
• Article: Strong Competition of Superconducting and Magnetic Order Parameters in Ba1-xNaxFe2As2

  Hemke Maeter, Gwendolyne Pascua, Hubertus Luetkens, Johannes Knolle, Saicharan Aswartham, Sabine Wurmehl, Günter Behr, Bernd Büchner, Zurab Shermadini, Kamil Sedlak, Alex Amato, Roderich Moessner, Ilya Eremin, Hans-Henning Klauss
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  ABSTRACT: We study the interplay of magnetic and superconducting order in single crystalline hole doped Ba1-xNaxFe2As2 using muon spin relaxation. We find microscopic coexistence of magnetic order and superconductivity. In a strongly underdoped specimen the two forms of order coexist without any measurable reduction of the ordered magnetic moment by superconductivity, while in a nearly optimally doped sample the ordered magnetic moment is strongly suppressed below the superconducting transition temperature. This coupling can be well described within the framework of an effective two-band model incorporating inter- and intra-band interactions. In optimally doped Ba1-xNaxFe2As2 we observe no traces of static or dynamic magnetism and the temperature dependence of the superfluid density is consistent with two s-wave gaps without nodes.
  10/2012;
• Source

  Available from: Jens Hänisch

  Article: Generic Fe buffer layers for Fe-based superconductors: Epitaxial FeSe1-xTex thin films

  Kazumasa Iida, Jens Haenisch, Michael Schulze, Saicharan Aswartham, Sabine Wurmehl, Bernd Buechner, Ludwig Schultz, Bernhard Holzapfel
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  ABSTRACT: Biaxially textured FeSe1-xTex films have been realized on Fe-buffered MgO substrates by pulsed laser deposition. Similar to the Fe/BaFe2As2 bilayers, the crystalline quality of FeSe1-xTex films exhibit a sharp out-of-plane and in-plane texture less than 0.9{\deg}. The Fe/FeSe1-xTex bilayers showed high superconducting transition temperatures of over 17 K. The angular-dependent critical current densities exhibit peaks positioned at H // ab similar to other pnictide thin films. The volume pinning force of FeSe1-xTex in this direction is very strong compared with that of Co-doped BaFe2As2, due to a good matching between the interlayer distance in the c direction and the out-of-plane coherence length.
  11/2011;
• Source

  Available from: Jeroen van den Brink

  Article: 75As NMR-NQR study in superconducting LiFeAs

  Seung-Ho Baek, Hans-Joachim Grafe, Franziska Hammerath, Madeleine Fuchs, Christian Rudisch, Luminita Harnagea, Saicharan Aswartham, Sabine Wurmehl, Jeroen van den Brink, Bernd Büchner
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  ABSTRACT: We report results of 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments as well as 7Li NMR on different samples of self flux grown LiFeAs and 5 % Co doped LiFeAs single crystals, and a polycrystalline LiFeAs sample. We were able to distinguish the samples by their slightly different quadrupole frequencies, $\nu_Q$, which is a direct measure of the electric field gradient (EFG) at the As site. Interestingly, samples with a large quadrupole frequency appear to show a different Knight shift and spin lattice relaxation in the superconducting state from those with a lower $\nu_Q$, yet all the samples are clearly superconducting. For sample S1 which has the largest $\nu_Q$, we find constant Knight shift K across Tc for a certain direction of the magnetic field and a peculiar upturn of the NQR spin lattice relaxation rate 1/T1 below Tc. In contrast, samples with a lower $\nu_Q$ exhibit the expected behavior for a singlet superconductor: a drop of K and 1/T1 for both NMR and NQR below Tc. Our results show that already tiny changes in stoichiometry uncovered by slightly different NQR frequencies lead to very different behavior of the NMR parameters in the superconducting state of LiFeAs. Different possibilities will be discussed which may explain the contrasting behavior.
  08/2011;