Grain boundary engineering with gold nanoparticles

We investigated high-T C grain boundary Josephson junctions with and without incorporated gold nanoparticles. Pulsed laser deposition was used for the deposition of YBa 2 Cu 3 O 7−δ thin films on SrTiO 3 bicrystal substrates with different grain boundary angles. During the deposition process, single-crystalline nanoparticles self-assembled from a thin gold layer which was sputtered on the substrate before the YBCO deposition. The interaction between nanoparticles and thin film growth significantly influences the quality of the YBCO films [1]. The critical current density and the critical temperature of the superconducting films can be increased in a defined manner. Furthermore, the nanoparticles influence the growth conditions in the region of the grain boundary and thus the properties of the later patterned Josephson junctions. The comparison between Josephson junctions with and without nanoparticles on the same substrate shows a reduction of the critical current I C and an increase of the normal state resistance RN for all investigated types of grain boundaries in the areas with gold nanoparticles. In some cases we even found an increase of the resulting I C R N product. We present the influence of light irradiation on the properties of the Josephson junctions

Influence of the spreading resistance on the conductance spectrum of planar hybrid thin film SNS' junctions based on iron pnictides

To investigate the superconducting properties of iron pnictides we prepared planar hybrid SNS' junctions in thin film technology with a pnictide base electrode, a gold barrier layer and a lead counter electrode. Our design allows characterization of the electrodes and the junction independently in a 4-probe method. We show how both electrodes influence the measured spectra due to their spreading resistance. While the Pb electrode has a constant resistance above its $T_c$, the contribution of the pnictide electrode is clearly current-dependent and thus it needs a more advanced method to be corrected. We present an empirical method, which is simple to apply and allows to deal with the spreading resistance in our junctions to recalculate the actual conductance and voltage of one junction at given temperature

Josephson and tunneling junctions with thin films of iron based superconductors

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

Josephson and tunneling junctions with thin films of iron based superconductors

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

The Next Generation of Cryogenic Current Comparators for Beam Monitoring

A new Cryogenic Current Comparator with eXtendedDimensions (CCC-XD), compared to earlier versions builtfor GSI, is currently under development for a non-destructive,highly-sensitive monitoring of nA-intensities ofbeams for larger beamline diameters planned for the newFAIR accelerator facility at GSI. The CCC consists of a:1) flux concentrator,2) superconducting shield against external magneticfield and a3) superconducting toroidal coil of niobium which isread out by a4) Superconducting Quantum Interference Device(SQUID).The new flux concentrator (1) comprises a specially designedhighly-permeable core made of nano-crystallinematerial, in order to assure low-noise operation with highsystem bandwidth of up to 200 kHz. The superconductingshielding of niobium (2) is extended in its geometric dimensionscompared to the predecessor CCC and thus willsuppress (better -200 dB) disturbing magnetic fields of thebeamline environment more effectively. For the CCD-XDreadout, new SQUID sensors (4) with sub-μm Josephsonjunctions are used which enable the lowest possible noiselimitedcurrent resolution in combination with a good suppressionof external disturbances.The CCC-XD system, together with a new dedicated cryostat,will be ready for testing in the CRYRING at GSI inspring 2017. For the application of a CCC in the antiprotonstorage ring at CERN a pulse shape correction has been developedand tested in parallel. Results from electricalmeasurements of two components (1 and 4) of the newCCC-XD setup will be presented in this work