Critical field anomalies of thin superconducting films with implanted helium particles

The influence of helium ion implantation on the parallel critical field Hc∥ and the angular dependence of Hc in In films has been investigated. It has been observed that the dependence of Hc∥ on the temperature, the film thickness d, and the mean free path l agrees satisfactorily with the predictions of theory for low doses of irradiation (N ≤7⋅1017 ion/cm1). For high irradiation doses a number of anomalies is observed in the behavior of Hc∥ and the angular dependence of Hc: The value of the critical thickness at which a vortex stale occurs in a film in a parallel magnetic field turns out to be substantially smaller than predicted by the Abrikosov–Kulik theory; a deviation from the angular dependence of Hc computed by Tinkham is detected in the temperature range T ∼ Tc, where ξ (t) ≫ d for high irradiation doses Hc∥ diminishes with a decrease in l. It is shown that the first two anomalies in the behavior of Hc∥ and HC(θ) can be explained by anisotropies of the transport properties, and therefore, in the coherence lengths in indium films with helium implantation. The last anomaly is associated with the effect of film swelling because of the formation of volume defects in the form of gas-filled pores therein. The possibility of an analogy between In films with helium implantation and laminar superconductors is examined.

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