Critical currents of thin films and their relation to inhomogeneities of superconductor parameters

The influence of implanting helium ions on the critical current of thin indium films in a perpendicular magnetic field is investigated. The critical current in a mixed state diminishes, as a rule, with an increase in the exposure dosage in the weak magnetic field range Hcr1≪H≪Hcr2. The dependences observed experimentally of the critical current on the temperature, magnetic field, and exposure dose are described well by the Larkin-Ovchinnikov theory which takes account of the influence of spatial inhomogeneities in the mean free path l and the interelectron interaction constant g on the critical current. It follows from a comparison with theory that a vortex lattice is realized in the films investigated, where the shear modulus C66 of the vortex lattice in the film changes with a reduction in temperature because of the change in sign of the inequality between the vortex lattice parameter and the effective penetration depth. A comparison between experimental results and theory also permits making the deduction that indium films become more homogeneous because of exposure.

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