Boson-fermion fluctuation dominated model of the superconducting transition in hole-underdoped cuprates

Reliable correlation of simultaneously measured resistively, susceptibility and specific heat critical parameters of hole-underdoped YBCO permitted to establish a phenomenological model of normal-superconductor transition. After the model, fluctuations of quasifree electrons drives at T* >> TC the appearance of paired charge carriers (pseudogap-PG) characterized by partial coherence of the order parameter's phase. The evolution of PG state from T* ∼ 140 K to the critical temperature TC ∼ 92 K is connected to the average increase of the statistically distributed partial coherence lifetime (from τ ∼ ps to ∞) and coherence length (from λ ∼ nm to ∞) of the fluctuating precursor islands. In this dynamic process the specific heat's maximum signals (at temperature TCC ∼ 93.6 K) the appearance of the first mesoscopic coherent islands. TC marks the percolation of these islands. We believe that the presented concept of dynamical evolution (in coherence time and space from 0 to ∞) of the paired charge structures is a promising scenario while describing the properties of hole doped high-TC superconductors between the temperatures T* and TC