We study the temperature dependence of the low energy phonons in the \((H,0,L)\) reciprocal plane of the highly ordered ortho-II YBa₂Cu₃O_6.55 cuprate high temperature superconductor by means of high-resolution inelastic x-ray scattering. Anomalies associated with the emergence of long-range charge density wave (CDW) fluctuations are observed, and are qualitatively similar to those previously observed in the \((0,K,L)\) plane. This confirms the unconventional nature of this bi-dimensional CDW, which is not soft-phonon driven. With the support of first principles calculations, the symmetry of the anomalous phonon is identified and is found to match that of the charge modulation. This suggests in turn that these anomalies originate from a direct coupling between the phonons and the collective CDW excitations.

中文翻译：

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YBa2Cu3O6+x 中低能声子异常的面内各向同性

我们研究了低能声子的温度依赖性 \((H,0,L)\)通过高分辨率非弹性 X 射线散射，高度有序的 ortho-II YBa ₂ Cu ₃ O _6.55铜酸盐高温超导体的倒易平面。观察到与出现长程电荷密度波 (CDW) 波动相关的异常，并且在性质上与先前在\((0,K,L)\)飞机。这证实了这种非软声子驱动的二维 CDW 的非常规性质。在第一性原理计算的支持下，异常声子的对称性被识别并发现与电荷调制的对称性相匹配。这反过来表明这些异常源于声子和集体 CDW 激发之间的直接耦合。