Effect of Self-Incandescent Heating on Superconducting NbN Nanowire Yarn

A flexible superconducting yarn composed of twisted niobium nitride (NbN) nanofibrils is developed and exhibited a superconducting transition temperature that met the reported record of ≈17 K. NbN is sputter-deposited onto a template of aligned single-layer carbon nanotube (CNT) sheets and subsequently processed by post-Joule heat annealing following the insertion of twists. Considering self-Joule heating approaches the level of incandescent light emission, the melting, reflow, and recrystallization of the NbN layer around each CNT template occurred, considerably enhancing the macroscopic superconducting properties of the NbN nanofibrillar yarn, including the critical current density and critical magnetic field. Furthermore, the superconducting performance, which degrades as a result of mechanical damage to the internal structure under excessive stress such as bending, can be restored by the reflow of the NbN during this process. Considering the melting point of NbN is higher than 2800 K, the proposed incandescent light-emission-driven Joule self-heating process is considered an effective method for improving the properties of CNT-templated metal hybrid yarns.