As a newly emergent type-II Dirac semimetal, Platinum Telluride (PtTe2) stands out from other 2D noble-transition-metal dichalcogenides for the unique structure and novel physical properties, such as high carrier mobility, strong electron-phonon coupling and tunable bandgap, which make the PtTe2 a good candidate for applications in optoelectronics, valleytronics and far infrared detectors. Although the transport properties of PtTe2 have been studied extensively, the dynamics of the nonequilibrium carriers remain nearly uninvestigated. Herein we employ optical pump-terahertz (THz) probe spectroscopy (OPTP) to systematically study the photocarrier dynamics of PtTe2 thin films with varying pump fluence, temperature, and film thickness. Upon photoexcitation the THz photoconductivity (PC) of 5 nm PtTe2 film shows abrupt increase initially, while the THz PC changes into negative value in a subpicosecond time scale, followed by a prolonged recovery process that lasted hundreds of picoseconds (ps). This unusual THz PC response observed in the 5 nm PtTe2 film was found to be absent in a 2 nm PtTe2 film. We assign the unexpected negative THz PC as the small polaron formation due to the strong electron-Eg-mode phonon coupling, which is further substantiated by pump fluence- and temperature-dependent measurements as well as the Raman spectroscopy. Moreover, our investigations give a subpicosecond time scale of sequential carrier cooling and polaron formation. The present study provides deep insights into the underlying dynamics evolution mechanisms of photocarrier in type-II Dirac semimetal upon photoexcitation, which is fundamental importance for designing PtTe2-based optoelectronic devices.
Transient terahertz photoconductivity measurements of minority-carrier lifetime in tin sulfide thin films: Advanced metrology for an early-stage photovoltaic material
Thickness-Dependent Spintronic Terahertz Emission in MBE-Grown PtTe$_2$: From Semiconductor to Type-II Dirac Semimetal
Univ. Grenoble Alpes, CEA, CNRS, IRIG-SPINTEC（格勒诺布尔阿尔卑斯大学、法国原子能和替代能源委员会、法国国家科学研究中心、IRIG自旋技术中心）；Centre for Nanodiagnostics of Materials, Faculty of Materials Science and Technology, Slovak University of Technology（材料纳米诊断中心、材料与科技学院、斯洛伐克科技大学）
Temperature evolution of quasiparticle dispersion dynamics in semimetallic 1T-TiTe2 via high-resolution angle-resolved photoemission spectroscopy and ultrafast optical pump-probe spectroscopy
Ultrafast dynamics of the low frequency shear mode in $\mathrm{1T'-MoTe_2}$
本文报道了利用飞秒泵浦-探测光谱研究半金属1 T '-MoTe 2中相干声子的动力学。在室温下的超快亚皮秒时间尺度上，在0.39 THz处观察到低频和长寿命的剪切声子模式，这是以前报道的仅在低温Td-MoTe 2相中以特征声子的形式存在。与其他光学声子模不同，剪切声子模与光激发载流子强耦合。此外，剪切模式的振幅令人惊讶地随着激发密度的增加而降低，这种现象可以归因于激发后晶格温度升高的结果。这些结果提供了有用的物理信息之间的正常的半金属1 T '和晶格反转对称性破缺II型Weyl半金属Td相的超快晶格对称性切换。
Magnetoterahertz Response and Faraday Rotation from Massive Dirac Fermions in the Topological Crystalline Insulator Pb$_{0.5}$Sn$_{0.5}$Te
Pb $_{1-x}$ Sn $_x$ Te已被证明是一个有趣的可调拓扑晶体绝缘体系统。本文对Pb $_{0.5}$ Sn $_{0.5}$ Te薄膜的磁太赫兹光谱进行了研究。在没有任何附加假设的情况下，提取了圆基中的复法拉第旋转角和光学电导率。我们的太赫兹响应的定量测量使我们能够表明，所研究的样品包含两种类型的散装船。一种是$p$型，起源于三维狄拉克带。另一个是$n$型，似乎来自更传统的3D波段。这两种类型的载体显示不同的回旋共振色散。通过模拟空穴载流子的回旋共振，可以确定费米能级和费米速度。此外，$p$型和$n$型载流子的散射率表现出相反的场依赖性，这可能是由于它们在磁场下不同的朗道能级展宽行为。我们的工作为分离Dirac和Weyl半金属中体态的实拓扑特征提供了一种新的方法。
