Pseudogap state in slightly doped by aluminium and praseodymium   YBa$_2$Cu$_3$O$_{7-\delta}$ single crystals with a given topology of plane   defects
  In present work the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries has been investigated. The excess conductivity for the analyzed samples shows dependence like $\Delta\sigma\sim(1-T/T^*)\exp(\Delta_{ab}^*/T)$ in wide temperature range $T_f<T<T^*$, where $T^*$ can be represents as mean field temperature of superconducting transition. The temperature dependence of pseudogap can be satisfactory described in terms of the BCS-BEC crossover theoretical model. 
R. V. Vovk, M. A. Obolenskii, A. A. Zavgorodniy, D. A. Lotnyk, K. A.   Kotvitskaya