[论文解读] Berry Curvature Enhanced Nonlinear Photogalvanic Response of Type-II Weyl Cone

Junchao Ma, Qiangqiang Gu+8 more|arXiv (Cornell University)|Jun 22, 2018

Topological Materials and Phenomena参考文献 35被引用 73

一句话总结

本文证明 TaIrTe4 中 Type-II Weyl 节点处的 Berry 曲率奇点会增强非线性光伏效应，产生由三阶非线性光学驱动的室温高光响应。

ABSTRACT

The experimental manifestation of topological effects in bulk materials under ambient conditions, especially those with practical applications, has attracted enormous research interest. Recent discovery of Weyl semimetal provides an ideal material platform for such endeavors. The Berry curvature in a Weyl semimetal becomes singular at the Weyl node, creating an effective magnetic monopole in the k-space. A pair of Weyl nodes carry quantized effective magnetic charges with opposite signs, and therefore, opposite chirality. Although Weyl-point-related signatures such as chiral anomaly and non-closing surface Fermi arcs have been detected through transport and ARPES measurements, direct experimental evidence of the effective k-space monopole of the Weyl nodes has so far been lacking. In this work, signatures of the singular topology in a type-II Weyl semimetal TaIrTe4 is revealed in the photo responses, which are shown to be directly related to the divergence of Berry curvature. As a result of the divergence of Berry curvature at the Weyl nodes, TaIrTe4 exhibits unusually large photo responsivity of 130.2 mA/W with 4-μm excitation in an unbiased field effect transistor at room temperature arising from the third-order nonlinear optical response. The room temperature mid-IR responsivity is approaching the performance of commercial HgCdTe detector operating at low temperature, making Type-II Weyl semimetal TaIrTe4 of practical importance in terms of photo sensing and solar energy harvesting. Furthermore, the high shift photocurrent response at the Weyl cones is found to enhance the circularly polarized galvanic response from Weyl cones with opposite chirality, which opens new experimental possibilities for studying and controlling the chiral polarization of Weyl Fermions through an in-plane DC electric field in addition to the optical helicities.

研究动机与目标

• 在常温条件下激励在体材料中寻找拓扑特征。
• 研究 Weyl 节点处的 Berry 曲率奇点如何影响非线性光学响应。
• 量化光响应并评估用于传感与太阳能的潜在器件应用。
• 展示 Weyl 节点手性与 Berry 曲率在光激发下如何影响电流产生。

提出的方法

• 将 TaIrTe4 分析为在 Weyl 节点具有奇异 Berry 曲率的 Type-II Weyl 半金属。
• 在无偏场的场效应晶体管中测量中红外、4-μm 激发下的光响应。
• 将观测到的响应归因于 Weyl 节点附近 Berry 曲率的发散。
• 将三阶非线性光学贡献确认为响应机制。
• 评估与 Weyl 锥手性相关的圆偏振光致电流响应。

实验结果

研究问题

• RQ1 Weyl 节点处 Berry 曲率的发散如何影响 Type-II Weyl 半金属中的非线性光伏效应？
• RQ2 TaIrTe4 是否能展现由三阶非线性过程驱动的室温大光响应？
• RQ3 Weyl 节点手性是否在平面电场下增强圆偏振光致电流？
• RQ4 在中红外波段，TaIrTe4 用于光探测和太阳能收集的实用性如何？

主要发现

• 在无偏 FET 中，4-μm 激发下室温出现异常高的光响应度 130.2 mA/W。
• 响应来源于三阶非线性光学响应。
• 观测到的响应反映了 Weyl 节点处 Berry 曲率的发散。
• Weyl 的扭曲处的高迁移光电流在相反手性之间增强圆偏振光致电流响应。
• 中红外室温性能接近低温 HgCdTe 探测器的水平，意味着实际传感潜力。