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- ItemFemtosecond spectroscopy in a nearly optimally doped Fe-based superconductors FeSe0.5Te0.5 and Ba(Fe 1-xCox)2As2/Fe thin film(Bristol : Institute of Physics Publishing, 2014) Bonavolontà, C.; Parlato, L.; De, Lisio, C.; Valentino, M.; Pepe, G.P.; Kazumasa, I.; Kurth, F.; Bellingeri, E.; Pallecchi, I.; Putti, M.; Ferdeghini, C.; Ummarino, G.A.; Laviano, F.Femtosecond spectroscopy has been used to investigate the quasi-particle relaxation times in nearly optimally doped Fe-based superconductors FeSe 0.5Te0.5 and optimally doped Ba-122 thin films growth on a Fe buffer layer. Experimental results concerning the temperature dependence of the relaxation time of such pnictides both in the superconducting state are now presented and discussed. Modelling the T-dependence of relaxation times an estimation of both electron-phonon constant and superconducting energy gap in the excitation spectrum of both Fe(Se,Te) and Ba-122 compounds is obtained.
- ItemJosephson and tunneling junctions with thin films of iron based superconductors(Amsterdam [u.a.] : Elsevier, 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.
- ItemA superconducting levitation transport model system for dynamical and didactical studies(Amsterdam [u.a.] : Elsevier, 2012) Rosenzweig, St.; Reich, E.; Neu, V.; Berger, D.; Peukert, K.; Holzapfel, B.; Schultz, L.; Pospiech, G.Superconducting levitation transport systems might become very attractive in the near future due to various reasons. The realisation of contactless systems allows e.g. extended maintenance-free operation with high efficiency since such a system only needs energy for cooling and propulsion. We established a small superconducting levitation transport model system called "SupraTrans Mini" consisting of permanent magnetic rails and a levitated vehicle including four YBCO-bulk samples in a cryostat. The rail system consists of an oval shaped loop (2.90 m x 1.44 m), which was build up from individual linear and curved track modules. Inside the vehicle position variations of the superconductors are possible. By means of velocity, acceleration and temperature measurements different dynamical aspects of our complex levitation system can be investigated. We also show the broad applicability of the experimental setup for didactical studies in physics.
- ItemSuperconductivity in multi-phase Mg-B-O compounds(Amsterdam [u.a.] : Elsevier, 2012) Prikhna, T.; Gawalek, W.; Eisterer, M.; Weber, H.W.; Noudem, J.; Sokolovsky, V.; Chaud, X.; Moshchil, V.; Karpets, M.; Kovylaev, V.; Borimskiy, A.; Tkach, V.; Kozyrev, A.; Kuznietsov, R.; Dellith, J.; Shmidt, C.; Basyuk, T.; Litzkendorf, D.; Karau, F.; Dittrich, U.; Tomsic, M.Structures of MgB2-based materials manufactured under pressure (up to 2 GPa) by different methods having high superconducting performance and connectivity are multiphase and contain different Mg-B-O compounds. Some oxygen can be incorporated into MgB2 and boron into MgO structures, MgBx (X=4-20) inclusions contain practically no oxygen. Regulating manufacturing temperature, pressure, introducing additions one can influence oxygen and boron distribution in the materials and thus, affect the formation, amount and sizes of Mg-B-O and MgBx inclusions and changing type of pinning, pinning force and so affect critical current density jc. The boron concentration increase in initial Mg and B mixture allows obtaining sample containing 88.5 wt% of MgB12 with Tc of 37.4 K (estimated magnetically).
- ItemPinning and trapped field in MgB2- and MT-YBaCuO bulk superconductors manufactured under pressure(Bristol : IOP Publ., 2016) Prikhna, T.; Eisterer, M.; Chaud, X.; Weber, H.W.; Habisreuther, T.; Moshchil, V.; Kozyrev, A.; Shapovalov, A.; Gawalek, W.; Wu, M.; Litzkendorf, D.; Goldacker, W.; Sokolovsky, V.; Shaternik, V.; Rabier, J.; Joulain, A.; Grechnev, G.; Boutko, V.; Gusev, A.; Shaternik, A.; Barvitskiy, P.The relevant pinning centers of Abrikosov vortices in MgB2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgBx (x>4) phases. The high critical current densities, jc, of 106 and 103A/cm2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB2 structure in small amounts (MgB1.5O0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The jc of melt textured YBa2Cu3O7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y2BaCuO5 (Y211) inclusions in Y123. At 77 K jc=8·104 A/cm2 in self-field and jc=103 A/cm2 at 10 T were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per µm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB2 to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.