Thickness dependence of flux-line-lattice melting in high-Tc superconducting films.

Civale et al. have recently measured the irreversibility line of YBa2Cu307 „(YBCO)films in the magnetic field-temperature plane, B;„(T),as a function of film thickness. We are able to reproduce the observed shift of B;„(T) to lower temperatures as the film thickness is reduced within a model of Aux-linelattice melting without pinning. While pinning must be important, this suggests B;„(T) is at least partly 0 an intrinsic property. The onset of the shift of B;„(T)begins for films thinner than 1000—1500 A in 0 YBCO. The present model predicts that the onset will begin for films thinner than 100—150 A in