ZrTe$_3$中电荷密度波序的高度各向异性瞬态光学响应
Highly anisotropic transient optical response of charge density wave order in ZrTe$_3$
AI总结：
本研究通过偏振双色泵浦探测测量，揭示了准一维材料ZrTe$_3$中CDW态的高度面内各向异性瞬态光学响应，发现不同偏振方向对CDW能隙的敏感度及AM振荡的寿命与持续性存在显著差异。
摘要：
CDW系统中的低维性导致平衡和非平衡条件下的各向异性光学性质。我们在准一维材料ZrTe$_3$上进行了偏振双色泵浦探测测量，以研究CDW态中的各向异性瞬态光学响应。观察到了面内各向异性，其与探测光子的偏振有关。在$T_\mathrm{CDW}$以下，当$\mathbf{E}_\mathrm{pr}$近似平行于$a$轴（$\mathbf{E}_\mathrm{pr} \parallel a$）时，准粒子弛豫信号和振幅模式（AM）振荡信号均远大于$\mathbf{E}_\mathrm{pr}$平行于$b$轴（$\mathbf{E}_\mathrm{pr} \parallel b$）的情况。这表明$\mathbf{E}_\mathrm{pr} \parallel a$信号对CDW能隙的变化更为敏感。有趣的是，$\mathbf{E}_\mathrm{pr} \parallel b$下观察到的AM振荡寿命比$\mathbf{E}_\mathrm{pr} \parallel a$更长。此外，在高泵浦通量下，当$\mathbf{E}_\mathrm{pr} \parallel a$时电子序熔化且AM振荡消失，$\mathbf{E}_\mathrm{pr} \parallel b$的AM振荡响应仍然持续存在。我们讨论了导致这两种偏振之间异常差异的可能原因。
英文摘要：
Low dimensionality in CDW systems leads to anisotropic optical properties, in both equilibrium and non-equilibrium conditions. Here we perform polarized two-color pump probe measurements on a quasi-1D material ZrTe$_3$, in order to study the anisotropic transient optical response in the CDW state. Profound in-plane anisotropy is observed with respect to polarization of probe photons. Below $T_\mathrm{CDW}$ both the quasi-particle relaxation signal and amplitude mode (AM) oscillation signal are much larger with $\mathbf{E}_\mathrm{pr}$ nearly parallel to $a$ axis ($\mathbf{E}_\mathrm{pr} \parallel a$) than for $\mathbf{E}_\mathrm{pr}$ parallel to $b$ axis ($\mathbf{E}_\mathrm{pr} \parallel b$). This reveals that $\mathbf{E}_\mathrm{pr} \parallel a$ signal is much more sensitive to the variation of the CDW gap. Interestingly, the lifetime of the AM oscillations observed with $\mathbf{E}_\mathrm{pr} \parallel b$ is longer than $\mathbf{E}_\mathrm{pr} \parallel a$. Moreover, at high pump fluence where the electronic order melts and the AM oscillations vanish for $\mathbf{E}_\mathrm{pr} \parallel a$ , the AM oscillatory response still persists for $\mathbf{E}_\mathrm{pr} \parallel b$. We discuss possible origins that lead to such unusual discrepancy between the two polarizations.
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