单相1 VS $_2$中无电荷密度波时的电子局域化和可能的相分离
Electron localization and possible phase separation in the absence of a charge density wave in single-phase 1T-VS$_2$
摘要：
本文报道了在高压下制备的高纯1 T-VS $_2$粉末样品的结构、磁性和输运性质的系统研究。结果明显不同于先前通过从LiVS $_2$中脱嵌Li获得的结果。首先，在94 K以下，透射电子显微镜没有发现电荷密度波（CDW）.然而，\textit{ab initio}声子计算揭示了一个潜在的CDW不稳定性驱动的声学声子软化波矢量${\bf q}_{CDW} \approx$（0.21，0.21，0）先前报道的脱嵌样品。低温下V-S键距的反常膨胀进一步表明了潜在的晶格不稳定性。第二，红外光学吸收和电阻率测量给出了非金属性质的证据，与没有CDW相的观察一致。另一方面，磁化率和NMR数据表明，与\textit{ab initio}能带结构计算的本地化的时刻与金属载体的共存。这种差异是调和的无序或电子相关性导致的纳米尺度的金属和非金属域的相分离引起的电子本地化的图片。我们得出结论，1 T-VS $_2$是在边缘的CDW转变，并建议在Li脱层样品中的残留电子掺杂稳定了均匀的CDW相的金属属性。
英文摘要：
We report on a systematic study of the structural, magnetic and transport properties of high-purity 1T-VS$_2$ powder samples prepared under high pressure. The results differ notably from those previously obtained by de-intercalating Li from LiVS$_2$. First, no Charge Density Wave (CDW) is found by transmission electron microscopy down to 94 K. Though, \textit{ab initio} phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector ${\bf q}_{CDW} \approx$ (0.21,0.21,0) previously reported in de-intercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature. Second, infrared optical absorption and electrical resistivity measurements give evidence of non metallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with \textit{ab initio} band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and non-metallic domains in the nm scale. We conclude that 1T-VS$_2$ is at the verge of a CDW transition and suggest that residual electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase with metallic properties.
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