Effect of disorder on the exponent in the coherence region in high temperature superconductors

Effect of disorder on the electrical resistance near the superconducting transition temperature in the paracoherence region of high temperature YBa2Cu3O7−δ (YBCO) thin film superconductor is reported. For this, c-axis oriented YBa2Cu3O7−δ thin films having superconducting transition width varying between 0.27 K and 6 K were deposited using laser ablation and high pressure oxygen sputtering techniques. Disorder in these films was further created by using 100 MeV oxygen and 200 MeV silver ions with varying fluences. It is observed that the critical exponent in the paracoherence region for films with high transition temperature and small transition width is in agreement with the theoretically predicted value (γ = 1.33) and is not affected by disorder, while for films with lower transition temperature and larger transition width the value of exponent is much larger as compared to that theoretically predicted and it varies from sample to sample and usually changes with disorder induced by radiation. This difference in the behaviour of the exponent has been explained on the basis of differences in the strength of weak links and the transition between temperatures Tm and Tc is interpreted as a percolation like transition with disorder.