Dirac半金属Cd3As2的太赫兹辐射研究
Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission
摘要：
拓扑半金属材料是一种性能优良的热电材料，热电性是其重要的潜在应用之一，因此拓扑半金属材料的热电效应引起了人们极大的兴趣。本文通过研究Dirac半金属Cd_3As_2的瞬态光电流产生的太赫兹辐射，揭示了Dirac半金属Cd_3As_2的瞬态光电热响应，即光塞贝克效应和光能斯特效应。我们的激发偏振和功率依赖性证实了所观察到的太赫兹辐射是由于光电效应，而不是其他非线性光学效应。此外，当施加弱磁场（~0.4 T）时，响应清楚地表明与光塞贝克效应相比，瞬态光热电电流产生的数量级增强。这种增强支持的光能斯特电流产生在Cd 3As 2的双极运输性质。这些结果突出了基于能斯特效应的拓扑狄拉克半金属可以实现热电性能的增强，并且我们的瞬态研究为适用于非平衡态问题的高场环境的热电器件铺平了道路。由于高效的光电转换，大的THz发射通过光整流和光致伸缩效应与传统的半导体相媲美。
英文摘要：
The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd3As2, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd3As2. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.
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