Observation of unusual irreversible/reversible effects in a macroscopic cylindrical hole drilled in superconducting Bi–Sr–Ca–Cu–O

Abstract

Current–voltage ( I– V) measurements were carried out for different current sweep rates (d I/d t) of transport current at zero magnetic field ( H = 0) and H ≠ 0 in a polycrystalline sample of Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O x (BSCCO) with a macroscopic cylindrical hole (CH) drilled. Similar measurements were also performed in the same BSCCO sample without CH for a comparison before drilling CH. For the same values of H, T, and d I/d t taken for both samples, it was observed that hysteresis effects appear in I– V curves upon cycling of transport current in upward and downward directions which contain the increasing and decreasing current values, respectively. However these effects which are seen in I– V curves of BSCCO sample with CH is more prominent than that of the BSCCO sample without CH. Further, the irreversibility effects in I– V curves of the BSCCO sample without CH disappears for H ≠ 0 exhibiting nearly a linear behaviour, whereas the hysteretic behaviour in I– V curves of the BSCCO sample with CH is still observed. This interesting behaviour could be evaluated that macroscopic cylindrical hole improves pinning properties of sample acting as a macroscopic flux pinning center for flux lines.