Effects of hole doping and chemical pressure on the average superconducting kinetic energy of YBa₂Cu₃O_7-δ single crystals

We reported on M_ZFC(T) and M_FCC(T) reversible dc magnetizations of YBa₂Cu₃O_7-δ, Y_0.99Ca_0.01Ba₂Cu₃O_7-δ and YBa_1.75Sra_0.25Cu₃O_7-δ single crystals with a strong focus on the effects of Ca and Sr doping on the average superconducting kinetic energy density, k(T) of the YBa₂Cu₃O_7-δ The k(T) is used as a relevant tool to provide physical information about the HTSC paring mechanism. The determination of the k(T) from M_ZFC(T) and M_FCC(T) data is supported by virial theorem of superconductivity [k(T) = – MB]. The M_ZFC(T) and M_FCC(T) measurements were performed with a SQUID magnetometer to H ≤ 50kOe applied parallel to the c axis of the samples. The results show that the samples present a common k(T) behavior that is characterized by a maximum value for T ≤ T_c that gradually decreases as the temperature rises towards to the T_c, becoming null to T ≤ T_c. The magnetic field affects smoothly the k(T) data behavior. The k(T) results contrasting of our samples shows that the Ca and Sr doping promotes a reduction of its amplitude. A possible explanation to this feature could be associated to the fact that the hole doping character promoted by Ca doping and the chemical pressure effect motivated by Sr doping affects considerably the superconducting paring mechanism of the YBa₂Cu₃O_7-δ