Photoinduced Changes of the In-Plane and Out-Of-Plane Electronic Properties in YBa₂Cu₃O_x

We report on the photoinduced changes of the electronic properties of YBa₂Cu₃O_x (x ≈ 6.6) thin films, focussing on the electrical anisotropy in the normal and the superconducting state. The latter was determined from magnetoconductivity measurements, performed before and after light excitation, and fitting the experimental results to the Aslamazov–Larkin theory of superconducting order-parameter fluctuations. The normal-state anisotropy σab/σc was calculated from resistance measurements carried out on samples grown on vicinal substrates. We observed that the photodoping process enhanced superconducting coherence lengths ξc(0) and ξab(0), but reduced the superconducting anisotropy ξab(0)/ξc(0) at all studied temperatures. In contrast, σab/σc was enhanced by photodoping at low temperatures, but reduced at high temperature. Our results strongly suggest that two different mechanisms contribute to the photodoping process, with one affecting only the normal-state properties.