We measure the dispersion of the Cu-O bond-stretching phonon mode in the high-temperature superconducting parent compound ${\mathrm{Ca}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$. Our density functional theory calculations predict a cosine-shaped bending of the dispersion along both the $(\xi 00$) and $(\xi \xi 0$) directions, while comparison with previous results on ${\mathrm{Ca}}_{1.84}{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ show it only along $(\xi 00$), suggesting an anisotropic effect which is not reproduced in calculation. Comparison with isostructural ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_4$ and literature suggests that these calculations reproduce well the dispersion in the overdoped regime.

中文翻译：

---

Ca2-xCuO2Cl2化合物中掺杂引起的键拉伸声子软化的面内各向异性

我们测量了Cu-O键拉伸声子模式在高温超导母体化合物中的分散度 ${钙}_2{\mathrm{氧化铜}}_2{氯}_2$。我们的密度泛函理论计算预测了色散沿两个方向的余弦形弯曲$（\xi 00$）和 $（\xi \xi 0$）方向，并与之前的结果进行比较 ${钙}_{1.84}{\mathrm{氧化铜}}_2{氯}_2$ 只显示 $（\xi 00$），表明各向异性效应在计算中未重现。与同构比较${\text{啦}}_{2-X}{\text{r}}_X{\text{氧化铜}}_4$ 和文献表明，这些计算很好地再现了超掺杂状态下的色散。