Lüders bands in coated conductors: an in situ strain and transport magneto-optical investigation

The superconducting properties of coated conductors (CCs) have been investigated by magneto-optical (MO) imaging. The main originality of our MO set-up is its capability to combine both strain and transport measurements in the range 6-300 K with magneto-optical observations. Luders band formation under strain in the Hastelloy(R) substrate is revealed in MO experiments by the field penetration inside cracks in the DyBCO and MgO layers. A correlation between the damaging morphology, the critical current and the residual resistivity at 78 K versus strain has been established. The critical temperature variation is attributed to a degradation of the grain boundaries with mechanical deformation.