Far-infrared transmission study onNd1.85Ce0.15CuO4−ythin films

Far-infrared transmission of ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4-y}$ thin films ($T_c=19\mathrm{}$ K) has been measured in the frequency range of 15∼150 ${\mathrm{cm}}^{-1\mathrm{}}$. An energy-gap-like peak is observed in $\frac{T_s}{T_n}$ at 40 ${\mathrm{cm}}^{-1\mathrm{}}$ ($\equiv E_p$), corresponding to ${\mathrm{E}}_p\sim 3.0k{T}_c$, which is reminiscent of the BCS-type superconductors. On the other hand, both the temperature and magnetic-field dependence of the peak show a non-BCS-like behavior. Also, reducing $T_c$ to 12 K by oxygen depletion does not affect the peak energy, for which $E_p=4.8k{T}_c$ is extracted. The similarities of these observations to the case of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ are discussed.