Polaronic features similar to those previously observed in the photoinducedspectra of cuprates have been detected in the reflectivity spectra ofchemically doped parent compounds of high-critical-temperature superconductors,both $n$-type and $p$-type. In Nd$_2$CuO$_{4-y}$ these features, whoseintensities depend both on doping and temperature, include local vibrationalmodes in the far infrared and a broad band centered at $\sim$ 1000 cm$^{-1}$.The latter band is produced by the overtones of two (or three) local modes andis well described in terms of a small-polaron model, with a binding energy ofabout 500 cm$^{-1}$. Most of the above infrared features are shown to survivein the metallic phase of Nd$_{2-x}$Ce$_x$Cu0$_{4-y}$, Bi$_2$Sr$_2$CuO$_6$, andYBa$_2$Cu$_3$O$_{7-y}$, where they appear as extra-Drude peaks. The occurrenceof polarons is attributed to local modes strongly coupled to carriers, as shownby a comparison with tunneling results.
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机译：在高临界温度超导体的化学掺杂母体化合物（n $型和$ p $型）的化学反射光谱中，已经检测到与先前在铜酸盐的光致光谱中观察到的极化特征相似的特征。在Nd $ _2 $ CuO $ _ {4-y} $中，这些特征的强度取决于掺杂和温度，包括远红外的局部振动模式和以$ \ sim $ 1000 cm $ ^ {-1}为中心的宽带后一个频带是由两个（或三个）局部模式的泛音产生的，并且根据小极化子模型进行了很好的描述，其结合能约为500 cm $ ^ {-1} $。以上大多数红外特征都显示在Nd $ _ {2-x- $ Ce $ _x $ Cu0 $ __ {4-y} $，Bi $ _2 $ Sr $ _2 $ CuO $ _6 $，和YBa $ _2 $ Cu $ _3 $ O $ _ {7-y} $，它们以德鲁德峰出现。极化子的出现归因于与载流子强耦合的局部模式，如与隧穿结果的比较所示。
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