Systematic modification of electrical and superconducting properties of YBCO and nano-patterning of high-T_C superconducting thin films by light-ion irradiation

Irradiation of high-temperature superconducting (HTS) YBa₂Cu₃O_7-δ (YBCO) thin films with 75 keV He⁺ ions leads to a quasi-exponential increase of the in-plane (ρ_ab) and the out-of-plane (ρ_c) resistivity in the normal state and to a non-linear decrease of the critical temperature T_c with ion dose. In situ electrical measurements at room temperature reveal an irradiation-induced reduction of resistivity anisotropy ρ_c/ρ_ab and a slight relaxation of film resistivity after the ion irradiation is stopped. Ex situ measurements show a stretched-exponential relaxation of T_c and normal state resistivity that continues for several weeks after the ion irradiation. Irradiation of YBCO thin films by low-energy He⁺ ions through stencil masks results in local modification of the electrical and superconducting properties of the HTS material. We demonstrate that masked ion-beam lithography enables to produce structures smaller than 100 nm in size that have potential for applications in future superconducting nano-electronics.