A. L. Solovjov, L. V. Omelchenko, V. B. Stepanov, R. V. Vovk, H.-U. Habermeier, H. Lochmajer, P. Przysłupski, and K. Rogacki

Phys. Rev. B 94, 224505 (2016)94, 224505 (2016)

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 high-Tc superconductors (cuprates) below the representative temperature T^∗ >>Tc resulting in the PG opening. Within the model, the temperature dependencies of the PG, Δ^∗(T), for the samples with different number of the PrBCO layers (NPr) were analyzed in the whole temperature range from T^∗ down to Tc. Near Tc, σ(T ) was found to be perfectly described by the Aslamazov–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 NPr, finally resulting in the appearance of the pronounced maximum of Δ^∗(T) at high temperatures. The result is most likely due to increasing influence of the intrinsic magnetism of PrBCO (μPr ≈ 4μB) and suggests the possibility to search in that way the change of interplay between the superconductivity and magnetism in cuprates. 

Fig.1. Δ^∗(T)/Δmax as a function of T/T^∗ for studied YBCOPrBCO superlattice SL3 and sandwich SD2 compared with reference Fe-pnictide samples SmFeAsO_0.85 (Tc ≈ 55 K)  and EuFeAsO_0.85F₁₅ (Tc ≈ 11 K).