Effect of pulsed UV laser irradiation on the properties of crystalline YBa₂Cu₃O_7-δ thin films

The influence of UV laser irradiation on the physical properties of epitaxial YBa₂Cu₃O_7-δ (YBCO) thin (<1νm) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities E_ir≤160mJcm^-2, i.e.2-3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature T_c was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentration.