Vortex lattice matching effects and 1/ f-noise reduction in HTS films and devices equipped with regular arrays of artificial defects
In this contribution, we report (i) on the observation of commensurability effects between regular arrays of artificial defects and the vortex lattice in high-temperature superconductor (HTS) films and (ii) on the reduction of low-frequency 1/ f noise in high- Tc superconducting quantum interference devices (SQUIDs) caused by these regular arrays of artificial defects. Arrays of submicrometer holes (antidots) with periodicity down to 0.5 μm were patterned into YBCO thin films without deterioration of superconducting properties. Commensurability effects between the antidot and vortex lattice were observed via resistive and inductive measurements, which clearly prove the presence of an attractive interaction between vortices and antidots and the existence of multiquanta vortices. Consequently, the attractive interaction between antidots and vortices was used to reduce the vortex motion in superconducting devices, thus leading to a strong reduction of 1/ f noise. For a proof of the principle, YBCO films with antidot lattices (5 μm spacing) were mounted in flip-chip configuration onto bicrystal rf-SQUIDs. Commensurability between vortex lattice in film, fluxons in the bicrystal boundary and the antidot array was observed in the form of a strong reduction and increase of the 1/ f noise at discrete magnetic inductions, which are predicted by simple geometric considerations. The transfer of this very promising technology for 1/ f noise reduction to standard HTS SQUIDs used in applications (e.g., NDE, MGC) is presently under way.