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Bicrystalline grain boundary junctions of Co-doped and P-doped Ba-122 thin films
2014, Schmidt, S., Döring, S., Schmidl, F., Kurth, F., Iida, K., Holzapfel, B., Kawaguchi, T., Mori, Y., Ikuta, H., Seidel, P.
We prepared GB junctions of Ba(Fe0.9Co0.1)2As2 thin films on bicrystalline [00 l]-tilt SrTiO3 substrates. The junctions show clear Josephson effects. Electrical characterization shows asymmetric I-V characteristics which can be described within the resistively shunted junction (RSJ) model. A large excess current is observed. Their formal ICRN product is 20.2 μV at 4.2 K, which is decreased to 6.5 μV when taking Iex into account. Fabrication methods to increase this value are discussed. Additionally, measurements on GB junctions of BaFe2(As0.66P0.34)2 thin films on LSAT bicrystalline substrates are shown. Their symmetric RSJ/flux flow-behavior exhibits a formal ICRN product of 45 μV, whereas the excess corrected value is ll μV.
Josephson and tunneling junctions with thin films of iron based superconductors
2012, Schmidt, S., Döring, S., Tympel, V., Schmidl, F., Haindl, S., Iida, K., Holzapfel, B., Seidel, P.
We produced planar hybrid Superconductor - Normal metal - Superconductor (SNS') junctions and interfaceengineered edge junctions (SN'S' or SIS' with normal metal (N') or insulating (I) barrier) with various areas using Co-doped Ba-122 as base electrode. Varying the thickness of the Normal metal (gold) barrier of the planar junctions, we can either observe Josephson behavior at thinner gold thicknesses or transport dominated by Andreev reflection. The edge junctions seem to form a SN'S'-contact.
Ultrafast structural changes in SrTiO3 due to a superconducting phase transition in a YBa2Cu3O7 top layer
2010, Lübcke, A., Zamponi, F., Loetzsch, R., Kämpfer, T., Uschmann, I., Große, V., Schmidl, F., Köttig, T., Thürk, M., Schwoerer, H., Förster, E., Seidel, P., Sauerbrey, R.
We investigate the structural response of SrTiO3 when Cooper pairs are broken in an epitaxially grown YBa2Cu3O 7 top layer due to both heating and optical excitation. The crystal structure is investigated by static, temperaturedependent and time-resolved x-ray diffraction. In the static case, a large strain field in SrTiO3 is formed in the proximity of the onset of the superconducting phase in the top layer, suggesting a relationship between both effects. For the time-dependent studies, we likewise find a large fraction of the probed volume of the SrTiO3 substrate strained if the top layer is superconducting. Upon optical breaking of Cooper pairs, the observed width of the rocking curve is reduced and its position is slightly shifted towards smaller angles. The dynamical theory of x-ray diffraction is used to model the measured rocking curves. We find that the thickness of the strained layer is reduced by about 200 nm on a sub-ps to ps timescale, but the strain value at the interface between SrTiO3 and YBa2Cu3O7 remains unaffected. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.