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.

Negative refraction, which reverses many fundamental aspects of classical optics, can be obtained in systems with negative magnetic permeability and negative dielectric permittivity. This Letter documents an experimental realization of negative refraction at millimeter waves, finite magnetic fields, and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and superconducting thin films. In the present case the superconducting YBa2Cu3O7 layers provide negative permittivity while negative permeability is achieved via ferromagnetic (La:Sr)MnO3 layers for frequencies and magnetic fields close to the ferromagnetic resonance. In these superlattices the refractive index can be switched between positive and negative regions using external magnetic field as tuning parameter.

No abstract