Dose effect of heavy-ion irradiation on the critical exponents in YBa 2Cu 3O 7− x thin films

Abstract

We investigated the influence of densities of columnar defects on the critical exponents estimated from the critical scaling analysis of current–voltage characteristics in YBa 2C 3O 7− x thin films. To avoid the difference of background pinning between samples, the densities of columnar defects were controlled in one sample successively. The dynamic critical exponent z increased with increasing the densities of columnar defects from B φ=0.5–1.0 T. It was also found that the installed defects led to the appearance of peak in the magnetic field dependence of z, while such peak did not appear before irradiation. These results are explained by the percolation model considering the statistical distribution of the pinning strength rather than the vortex glass–liquid transition model. The various changes of z due to the heavy-ion irradiation are related to the change of the pinning strength distribution due to the introduction of columnar defects, which act as the strong pinning centers.