Response of the Double Layer Capacitance of a High-Temperature Superconductor/Fluid Electrolyte Interface to the Onset of Superconductivity

Measurements of interfacial (double layer) capacitance, C_dl, and charge transfer resistance, R_ct, have been made as a function of temperature at fluid electrolyte interfaces with electrodes made from two different Tl-based high-temperature superconductor materials. Measurements spanning the 112-119 K superconducting transition temperatures, T_c, of the HTSC electrodes reveal a smooth decrease in C_dl with decreasing temperatures, except that an abrupt, ca. 1 deg wide change in the shape of the C_dl vs temperature curve occurs at the T_c of the electrode. These are the first data which show that the onset of superconductivity can be reflected in a chemical phenomenon at a molecular fluid/HTSC interface. Of the several contributors to interfacial capacitance, it is hypothesized that alteration in charge carrier distribution or polarizability over the outermost electrode lattice layer as electron pairs start to appear at T_c is the most likely origin of the T_c-correlated capacitance feature. Alterations in the charge transfer resistance for electrochemical solvent reduction appear over the same temperature interval as the capacitance feature, but not as consistently.