C-axis tunneling in YBa2Cu3O7-delta trilayer junctions with PrBa2Cu3O7-delta barrier

This paper reports c-axis tunneling spectroscopy investigations of high-quality junctions fabricated from YBa2Cu3O7-delta/PrBa2Cu3O7-delta/YBa2Cu3O7-delta (YBCO/PBCO/YBCO) trilayers deposited by off-axis laser ablation. We observe a temperature-dependent BCS-like gap giving 2 Delta/k(B)T(C) = 1.3 and a finite subgap structure. The conductance spectra display parabolic behaviour at higher bias. These results indicate that even by using a 60 nm thick PBCO barrier it is possible to obtain SIS-like junctions in c-axis oriented YBCO. We obtain high I(C)R(N) values and an almost exponential dependence of junction resistance with temperature indicating that we are not observing transport through the PBCO via shorts. We show that quasiparticle transport in these junctions can be described by the Glazman-Matveev theory for hopping transport via localised states.