Evidence of Interface-Enhanced T$_{c}$ in Rare-Earth Doped Ca122

Nonbulk superconductivity with an onset-T$_{c}$ up to 49 K has been observed in single crystalline rare-earth doped CaFe$_{2}$As$_{2}$ [(Ca$_{1-x}$,RE$_{x})$122] recently. Such a T$_{c}$ is more than $\sim$ 20 K higher than any known compounds that consist of one or more of the Ca, RE, Fe and As elements at ambient or under high pressures. The unusually high onset-T$_{c}$ has therefore been attributed to interface effect. We have made systematic magnetic, transport, calorimetric and structural studies. They show: a chemically homogeneity of $\Delta $x \textless\ 0.005 over a 1$\mu$m; less than 5 {\%} of a bulk superconducting volume fraction; a doping-insensitive onset-T$_{c}$ in samples with or without the ``collapsed phase'', varying from $\sim$ 42 K for RE $=$ Nd to 49 K for RE $=$ Pr with a doping sensitive superconducting volume fraction, suggesting that the high onset-T$_{c}$ cannot be due to chemical doping or the effect of the ``collapsed phase''; an unusually high magnetic anisotropy up to 200, in contrast to the value of 4 from the sample geometric anisotropy, suggesting that the superconducting body has a very high aspect ratio; several steps in the magnetic susceptibilities along both the c- and ab-directions in the field range between 10$^{-3}$ to 10$^{+3}$ Oe, demonstrating the sample consisting of Josephson-Coupled superconducting islands imbedded with nano-scale interfaces; and the presence of superparamagnetic clusters associated with minute As-vacancies, consistent with theoretical calculations. The present studies therefore present the strongest evidence for interface-enhanced T$_{c}$ to date.