Investigation of the interface problem between high temperature superconductor and ionic conductors

The charge carriers transfer process across the interface between a superconductor and an ionic conductor, around T_c is investigated. Low temperature electrochemical measurements are carried out on the interfaces between different polycrystalline high-T_c superconductors (HTSC) and RbAg₄l₅ and Ag⁺ ion-conducting glass. The experiments cover a temperature range down to 10 K in the de-frequency range. Atransient technique in the time domain and electrochemical impedance spectroscopy (EIS) in the frequency domain are used to study the silver (Ag⁺) deposition as the Faradaic charge transfer process at that interface. The results show significant enhancement of the charge transfer observed around the critical temperature. This was indicated by either an admittance peak in the transient measurements or a corresponding decrease of the polarization resistance (R_p) in EIS measurements. This enhancement of the charge transfer is correlated to the formation of Cooper pairs at T ≤ T_c and interpreted on the basis of a band structure model as a quantumelectrochemical phenomenon with the tunnelling of Cooper pairs through the electrochemical double layer.