外尔半金属PtBi$_2$三维布里渊区的超快载流子动力学
Ultrafast carrier dynamics throughout the three-dimensional Brillouin zone of the Weyl semimetal PtBi$_2$
AI总结：
本研究利用时间分辨角分辨光电子能谱结合k-means机器学习，表征了I型外尔半金属PtBi$_2$三维布里渊区的超快载流子动力学，发现体费米面区域动力学快于外尔点附近。
摘要：
我们利用时间分辨和角分辨光电子能谱，研究了I型外尔半金属PtBi$_2$的未占据电子结构与电子动力学。借助宽范围调节探测光子能量的能力，我们在未占据三维能带结构中识别出了理论预言的外尔点，并讨论了通常未占据态中$k_\bot$展宽的效应。我们采用无监督机器学习技术k-means，表征了外尔点附近及三维布里渊区其他区域的电子动力学。结果揭示出显著差异：尤其是布里渊区中承载大部分体费米面的区域，其动力学过程比外尔点附近区域更快。
英文摘要：
Using time- and angle-resolved photoemission spectroscopy, we examine the unoccupied electronic structure and electron dynamics of the type-I Weyl semimetal PtBi$_2$. Using the ability to change the probe photon energy over a wide range, we identify the predicted Weyl points in the unoccupied three-dimensional band structure and we discuss the effect of $k_\perp$ broadening in the normally unoccupied states. We characterise the electron dynamics close to the Weyl point and in other parts of three-dimensional Brillouin zone using $k$-means, an unsupervised machine learning technique. This reveals distinct differences -- in particular, dynamics that are faster in the parts of the Brillouin zone that host most of the bulk Fermi surface than in parts close to the Weyl points.
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