EFFECTS OF HIGHT HYDROSTATIC PRESSURE ON DIFFERENT TYPES OF CONDUCTIVITY OF YBaCuO SINGLE CRYSTALS WITH A GIVEN TOPOLOGY OF PLANAR DEFECTS

Abstract

The e ect of high hydrostatic pressures of up to 10 kbar on the basal ab-plane conductivity of YBa2Cu3O7−δ single crystals with unidirectional twin boundaries is investigated. We show that application of a high pressure leads to a substantial decrease of the pressure derivative of the coherence length dξc/dP while increasing dTc/dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the frames of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling. The excess conductivity Δσ (T) in YBa2Cu3O7−δ has been revealed to obey an exponential dependence in the wide temperature range Tc<T <T*. At this, the description of the excess conductivity by the expression Δσ ~ (1 − T/T*) exp(Δ*ab/T ) can be interpreted in terms of the mean-field theory, where T* is the mean-field superconducting transition temperature and the pseudogap temperature dependence is satisfactory described within the framework of the BCS-BEC crossover theory. An increase of the applied pressure leads to a narrowing of the temperature range of the realization of the pseudogap regime, thereby expanding the linear temperature dependence of the ab-plane resistivity ρ(T).