温度驱动的层状错配化合物（LaS）$_{1.196}$ VS $_2$中的钒团簇化和带隙扩大
Temperature driven Vanadium clusterization and band gap enlargement in the layered misfit compound (LaS)$_{1.196}$VS$_2$
摘要：
通过输运、光学测量、角分辨光电子能谱（ARPES）和X射线衍射研究了错配层状硫族化合物（LaS）$_{1.196}$ VS $_2$晶体的有趣性质。虽然没有发现明显的异常，在运输性能作为温度的函数，一个大的光谱重量转移，至少1 eV，观察到的光学和光电子能谱。ARPES揭示了一个几乎充满的带负曲率，足够接近费米能级在300 K，以产生金属的行为，观察到的光学电导率谱。在低温下，能带结构被强烈地修改，产生具有120 meV的光学带隙的绝缘状态。一个准确的（3+1）D分析的X射线衍射数据表明，虽然没有发生相变，结构畸变增加，随着温度的降低，和钒簇化增强。我们发现电子性质的变化与结构的变化密切相关。这表明结构畸变在（LaS）$_{1.196}$ VS $_2$的绝缘性质中起主要作用，并且与先前的观点相反，电子相关性可能并不重要。这些结果为（LaS）$_{1.196}$ VS $_2$的非线性电性质的起源机制提供了新的线索。
英文摘要：
Intriguing properties of the misfit layered chalcogenide (LaS)$_{1.196}$VS$_2$ crystals were investigated by transport, optical measurements, angle-resolved photoemission (ARPES) and x-ray diffraction. Although no clear anomaly is found in transport properties as a function of temperature, a large spectral weight transfer, up to at least 1 eV, is observed by both optical and photoemission spectroscopies. ARPES reveals that a nearly filled band with negative curvature, close enough from the Fermi level at 300K to produce metallic-like behaviour as observed in optical conductivity spectra. At low temperature, the band structure is strongly modified, yielding to an insulating state with a optical gap of 120 meV. An accurate (3+1)D analysis of x-ray diffraction data shows that, although a phase transition does not occur, structural distortions increase as temperature is decreased, and vanadium clusterization is enhanced. We found that the changes of electronic properties and structure are intimately related. This indicates that structural distorsion play a major role in the insulating nature of (LaS)$_{1.196}$VS$_2$ and that electronic correlation may not be important, contrary to previous belief. These results shed a new light on the mechanism at the origin of non-linear electric properties observed in (LaS)$_{1.196}$VS$_2$.
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