Unusual behavior of pseudogap in high-temperature superconductors under the influence of external factors. Part II (Review article)

Within the framework of the developed theoretical approach, the temperature dependences of the resistivity ρ(T), excess conductivity σ′(T), and pseudogap (PG) Δ*(T) in YBa2Cu3O7–δ and Y1–xPrxBa2Cu3O7–δ (x = 0.05) single crystals under effect of high-energy electron irradiation and hydrostatic pressure up to 1.7 GPa were analyzed. It is shown that the effect of the external factors is rather specific. This specificity can be detected by analyzing the properties of the fluctuation conductivity and PG, which turned out to be much more sensitive to changes in the internal electronic subsystems caused by induced defects than the specific resistance. The unusual behavior of high-temperature superconductor single crystals under the influence of external factors is examined in detail.