Polikristal Bi(1,7)Pb(0,3)Sr(2)Ca(2)Cu(3)O(x) üstün iletkenlerde tersinmez taşıma olayları

The aim of this study is to investigate the magnetic flux dynamics in a polycrystalline sample of superconducting Bi(1.7)Pb(0.3)Sr(2)Ca(2)Cu(3)O(x) (BSCCO) with a macroscopic cylindrical hole (CH) drilled through the sample. Current-voltage (I ? V curves), transport relaxation (V ? t curves), and magnetovoltage (V ? H curves) measurements were carried out as functions of transport current (I), temperature (T), and external magnetic field (H) on the BSCCO sample before drilling the CH. Then, similar measurements were carried out on the same BSCCO sample after drilling the CH. The results can be summarized as follows:(i)The hysteresis effects in the I ? V curves of the sample without CH disappear for all dI/dt values at H 0, and the I ? V curves exhibit approximately linear behavior. However, the hysteresis effects in the I ? V curves of sample with CH are still observed for the same magnetic field, temperature and dI/dt values. The results suggest that the CH behaves as a macroscopic flux pinning center for the flux lines, which reduces the measured voltage dissipation by preventing the flux motion.(ii)In order to investigate the penetration of the driving current into the samples, a maximum current (Imax) was applied to the samples and decreased to zero with a certain value of dI/dt. Then, the current was increased from zero to Imax with the same value of dI/dt. The voltage humps which indicate the existence of an obstruction due to the surface effects and also by the presence of CH were observed at low values of Imax.(iii)The V ? t measurements of the sample with CH showed some discontinuties which were attributed to the leaving of flux lines via the CH and surface effects. In addition, we observed a new type of non-linear dynamic response to bidirectional square wave (BSW) current applied to the sample reflects itself as regular sinusoidal-like voltage oscillations.(iv)The V ? H curves measured for the sample with CH depend on the field ramping rate (dH/dt) and exhibit prominent counter clockwise hysteresis effects which are unusual when compared to those for the sample without CH.