Employing high-pressure infrared spectroscopy we unveil the Weyl semimetal phase of elemental Te and its topological properties. The linear frequency dependence of the optical conductivity provides clear evidence for metallization of trigonal tellurium (Te-I) and the linear band dispersion above 3.0 GPa. This semimetallic Weyl phase can be tuned by increasing pressure further: a kink separates two linear regimes in the optical conductivity (at 3.7 GPa), a signature proposed for Type-II Weyl semimetals with tilted cones; this however reveals a different origin in trigonal tellurium. Our density-functional calculations do not reveal any significant tilting and suggest that Te-I remains in the Type-I Weyl phase, but with two valence bands in the vicinity of the Fermi level. Their interplay gives rise to the peculiar optical conductivity behavior with more than one linear regime. Pressure above 4.3 GPa stabilizes the more complex Te-II and Te-III polymorphs, which are robust metals.

中文翻译：

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I型Weyl半金属的电导率中的两个线性形式：元素碲。

利用高压红外光谱，我们揭示了元素Te的Weyl半金属相及其拓扑性质。光导率的线性频率依赖性为三角碲（Te-I）的金属化和3.0 GPa以上的线性带色散提供了清晰的证据。可以通过进一步增加压力来调节这种半金属Weyl相：纽结将光导率（在3.7 GPa处）的两个线性区分开，这是针对具有倾斜圆锥的II型Weyl半金属提出的特征。然而，这揭示了三角碲的不同来源。我们的密度泛函计算没有发现任何明显的倾斜，并且表明Te-I保持在I型Weyl相中，但在费米能级附近具有两个价带。它们的相互作用产生了不止一种线性状态的特殊光导行为。高于4.3 GPa的压力可稳定更复杂的Te-II和Te-III多晶型物，它们是坚固的金属。