The pseudogap (PG) derived from the analysis of the excess conductivity σ ′ (T ) in superlattices and double-layer films of YBa2Cu3O 7−δ − PrBa2Cu3O 7−δ (YBCO-PrBCO), prepared by pulsed laser deposition, is studied for the first time. The σ ′ (T ) analysis has been performed within the local-pair (LP) model based on the assumption of the paired fermion (LPs) formation in the cuprate highTc superconductors (cuprates) below the representative temperature T * ≫ Tc resulting in the PG opening. Within the model, the temperature dependencies of the PG, ∆ * (T ), for the samples with different number of the PrBCO layers (NP r ) were analyzed in the whole temperature range from T * down to Tc. Near Tc, σ ′ (T ) was found to be perfectly described by the Aslamasov-Larkin (AL) and Hikami-Larkin (HL) [Maki-Thompson (MT) term] fluctuation theories, suggesting the presence of superconducting fluctuations in a relatively large (up to 15 K) temperature range above Tc. All sample parameters were found to change with increase of NP r , finally resulting in the appearance of the pronounced maximum of ∆ * (T ) at high temperatures. The result is most likely due to increasing influence of the intrinsic magnetism of PrBCO (µP r ≈ 4 µB) and suggests the possibility to search in that way the change of interplay between the superconductivity and magnetism in cuprates.

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The influence of hydrostatic pressure up to P=1.05 GPa on resistivity, excess conductivity σ ′ (T ) and pseudogap ∆ * (T ) is investigated in slightly doped single crystals of Y Ba2Cu3O 7−δ (Tc(P = 0) ≈49.2 K and δ ≈ 0.5). The critical temperature Tc is found to increase with increasing pressure at a rate dTc/dP = +5.1 KGP a −1 , while ρ(300) K decreases at a rate dlnρ/dP = (−19±0.2)% GP a −1 . Near Tc, independently on pressure, the σ ′ (T ) is well described by the Aslamasov-Larkin and HikamiLarkin fluctuation theories, demonstrating a 3D-2D crossover with increase of temperature. The crossover temperature T0 determines the coherence length along the c-axis ξc(0) ≃ (3.43 ± 0.01)Å at P=0, which is found to decrease with increasing P. At the same time, ∆ * and the BCS ratio 2∆ * /kB Tc both increase with increasing hydrostatic pressure at a rate dln∆ * /dP ≈ 0.36 GP a −1 , implying an increase of the coupling strength with increasing P. At low temperatures below Tpair, the shape of the ∆ * (T ) curve is found to be almost independent on pressure. At high temperatures, the shape of the ∆ * (T ) curve changes noticeably with increasing P, suggesting a strong influence of pressure on the lattice dynamics. This unusual behavior is observed for the first time.