Preparation And Transport Investigations Of The Flexible FeSe And Nb Superconducting Films

After the discovery of superconductivity 100 years ago,various superconducting systems have emerged and researches on physics and applications of superconductors have also been conducted steadily.In this paper,FeSe and Nb superconducting films were prepared on flexible substrates in view of the practical application of flexible superconductivity,such as low-temperature flexible superconducting circuits and radio-frequency applications,and the influence of bending on the superconductivity and vortex motion of superconducting films was investigated.This work provides a new gating method and research paradigm for the study of superconductivity.The main contents include:(1)FeSe thin films were deposited on KMg3Al(Si3O10)F2(F-mica)substrates by the pulsed laser deposition technology,and the deposition parameters have been explored carefully.After the substrate was cleaved into about 20μm by mechanical exfoliation method,the FeSe/F-mica sample exhibits good flexibility.We applied compressive(ε<0)and tensile(ε>0)strains to the film by bending the flexible FeSe/F-mica sample.It is found that the tensile strain is unfavorable to the superconductivity of FeSe films,the sample Tc0 decreases from 5.3 K to 5.0 K for ε=0.40%.Besides,the compressive strain is conductive to the superconductivity of FeSe films,the sample Tc0 increases from 5.3 K to 6.5 K forε=-0.41%.What’s more,the rate of superconducting transition temperature change is 28%.The experimental results are consistent with the physical image of superconductivity and nematic order competing.(2)In order to efficiently measure the electrical transport properties of the flexible superconducting thin films,we built a high-throughput test system based on PPMS.The core component of the system is the Keithley 7001 switching controller which can simultaneously measure electrical signals of 20 channels by a set of source tables.This system was utilized to characterize the flexible Nb/PI superconducting thin films,which has been patterned into multiple transport channels and glued on a quarter circular curved surface.The results show that the Tc of Nb film increases with the increase of the angle between the film normal and the magnetic field,i.e.,the surface of Nb film and the magnetic field tend to be parallel.Obviously,the weakening of the superconductivity compression in the film is due to a decrease in its vertical component,which reflects the anisotropy of the critical magnetic field of the superconducting film.(3)We studied and compared the electrical transport properties of the flexible Nb/PI and the rigid Nb/Al2O3 thin films under different angles and applied currents.When the angle is large,a series of resistivity plateaus appeared on the resistivity versus temperature(ρ-T)curves of the bending Nb/PI film for larger applied currents(I≥700 μA).The phenomenon may be caused by the gradient distribution of magnetic vortices in the bending films.Since the vortex density directly affects the interaction force between vortices,the high-density region will preferentially move due to a fixed current.In other words,the resistance platform arises from the piecewise motion of gradient-distributed vortices.