AI 中文总结
研究Na$_{0.5}$CoO$_2$中钠离子晶格动力学，采用偏振分辨拉曼光谱与第一性原理计算结合，首次检测到两种钠声子模式，发现其在特定温度下有异常，解释为动态到静态转变，为CoO$_2$层电子和磁有序奠定基础。
AI 中文摘要
我们采用偏振分辨拉曼光谱结合第一性原理计算，研究了钠之字形有序钴酸盐化合物Na$_{{0.5}}$CoO$_2$中的钠离子晶格动力学。首次检测到两种钠声子模式，其模式频率与基于正交晶胞的第一性原理声子计算结果一致。发现它们在$T^*\sim300\pm50$K以下出现，线宽大幅展宽，远低于钠之字形有序温度$T_\text{S}\sim460$K，然后在较低温度下变窄。我们将在$T^*$处出现的钠声子异常解释为主要涉及钠离子运动的动态到静态转变。结果表明，钠离子的逐渐冻结以及在$T^*$以下明确的静态钠之字形有序为Na$_{0.5}$CoO$_2$的CoO$_2$层中出现的电子和磁有序奠定了基础。
英文摘要
We employ polarization-resolved Raman spectroscopy combined with first-principles calculations to study the sodium-ion lattice dynamics in a sodium zig-zag ordered cobaltate compound Na$_{0.5}$CoO$_2$. We detect two sodium phonon modes for the first time, and their mode frequencies are consistent with first-principles phonon calculations based on an orthorhombic unit cell. We find that they appear below around $T^*\sim300\pm50$K with large linewidth broadening, much lower than the sodium zig-zag ordering temperature $T_\text{S}\sim460$K, and then narrow at lower temperatures. We interpret the sodium-phonon anomalies occurring at $T^*$ as a dynamical-to-static crossover involving mainly the motion of sodium ions. Our results suggest that the gradual freezing of the sodium ions and the well-defined static sodium-zigzag order below $T^*$ set the stage for the emergent electronic and magnetic orders in the CoO$_2$ layer of Na$_{0.5}$CoO$_2$.
Comments17 pages, 12 figures, to appear in Physical Review B
Journal refPhys. Rev. B 114, 105102 (2026)
