Conference Proceeding

Fabrication and characterization of electrospun superconducting Bi2Sr2CaCu2O8+x nanowires and nanowire networks

Dr. Michael R. Koblischka,
Saarland University, Germany

Dr. Michael R. Koblischka has studied Physics at Stuttgart University, and obtained his diploma and PhD from the Max-Planck Institute of Metal Research, Stuttgart. He had spent several years as a Postdoc at the Free University of Amsterdam (The Netherlands), the University of Geneva (Switzerland), the University of Oslo (Norway) and at Nordic Superconductors Technologies A/S in Denmark. Then, he had a two-years stay at the Superconductivity Research Laboratory (ISTEC), Division 3, in Tokyo, Japan. Since 2001, he has worked on his habilitation at Saarland University, Germany. Currently, he leads a research group on superconductivity in reduced dimensions.

Superconducting nanowires and nanowire networks of the high-Tc superconductor Bi2Sr2CaCu2O8+x (Bi-2212) were fabricated by means of electrospinning. Granular nanowires of considerable lengths of up to 100 µm and diameters between 100 and 250 nm result, forming a fabric-like structure with numerous interconnects between the individual nanowires. The resulting material has an extremely low density of only 0.05 g/cm3. These interconnects play an important role to enable the flow of transport currents through the entire network, so the samples were characterized by transmission electron microscopy. Resistance and U/I-measurements were performed in magnetic fields up to 10 T, and magnetization measurements were performed using a SQUID magnetometer. The resulting superconducting transition temperature, Tc, was found to be ~85 K, similar to bulk material. Due to influence of granularity, the field dependencies of the magnetization were analyzed using the extended critical state model. Single nanowires showed remarkably high values of the critical current density of 1.69 × 107 A/cm2 at 5 K. The resulting sample critical current density of 7.44 × 104 A/cm2 at 5 K is fine for this lightweight material. Individual nanowires were extracted from the nanowire networks by means of focused ion-beam milling and nanomanipulation to enable 4-point transport measurements. Several nanowires exhibited a semiconducting behavior before Tc is reached, and the onset temperature of superconductivity was found to be considerably lower than that of the network sample. The Tc showed, however, a clear current dependence, as the onset of superconductivity vanished at an applied current of 10 nA. This behavior is attributed to a spread of the superconducting properties within the nanowire network. Furthermore, we discuss possible applications of this new class of superconducting material.

Published: 27 April 2017