发表机构
The Institute for Solid State Physics, The University of Tokyo; Department of Electronic Science and Engineering, Kyoto University（东京大学固体物理研究所; 京都大学电子科学与工程系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过太赫兹偏振测量在氮化镓中非接触观测逆轨道霍尔效应，揭示空穴OAM-电荷转换及其亚皮秒弛豫，为轨道电子学提供关键见解。
AI 中文摘要
轨道电子学（Orbitronics）作为一种利用电子轨道角动量（OAM）而无需自旋-轨道耦合的信息存储与处理平台，已引起广泛关注。然而，OAM-电荷相互转换的实验评估仍是一个挑战，且由于体相与界面贡献的共存以及样品结构的复杂性，结果往往存在争议。在此，我们利用圆偏振光脉冲和太赫兹（THz）偏振测量，开发了一种非接触方法，在单一材料内将逆轨道霍尔效应作为体响应进行观测，而无需采用异质结构样品。在半导体GaN中，我们直接捕获了太赫兹频率范围内空穴的OAM到电荷电流的转换。通过分析霍尔电导率的尖锐频率依赖性，我们厘清了相互竞争的微观机制，并揭示了在直流极限下外在贡献对轨道霍尔效应的主导作用。相比之下，高于杂质散射率的太赫兹频率下的霍尔电导率则归因于内在的Berry曲率机制，从而能够与微观理论进行定量比较。此外，逆轨道霍尔信号的超快动力学直接揭示了空穴亚皮秒级的OAM弛豫，其时间尺度与声子介导的热化过程相当。基于理论计算的定量论证表明，由于声学声子引起的动量重新分布，存在一个更快的衰减通道，暗示OAM弛豫长度在亚纳米量级。我们的结果为OAM输运提供了全面而关键的见解，并建立了一种用于研究OAM到电荷转换的超快、非接触方法。
英文摘要
Orbitronics has attracted significant attention as a platform for information storage and processing that exploits the orbital angular momentum (OAM) of electrons without the need for spin-orbit coupling. However, experimental evaluation of OAM-charge interconversion remains a challenge and the results are often controversial due to the coexistence of bulk and interfacial contributions and the complexity in sample structures. Here, using circularly polarized light pulses and terahertz (THz) polarimetry, we developed a non-contact method to observe the inverse orbital Hall effect as a bulk response within a single material without employing heterostructure samples. In a semiconductor GaN, we directly captured the OAM-to-charge current conversion of holes in the THz frequency range. By analyzing the sharp frequency dependence of the Hall conductivity, we disentangled the competing microscopic mechanisms and revealed the dominant role of extrinsic contributions to the orbital Hall effect in the dc limit. By contrast, the Hall conductivity at THz frequencies above the impurity scattering rate is attributed to the intrinsic Berry-curvature mechanism,allowing a quantitative comparison with the microscopic theory. Furthermore, the ultrafast dynamics of the inverse orbital Hall signal directly revealed sub-picosecond OAM relaxation of holes, comparable to that of phonon-mediated thermalization. The quantitative argument based on theoretical calculations suggested the existence of an even faster decay channel due to momentum redistribution by acoustic phonons, suggesting a sub-nanometer-scale OAM relaxation length. Our results provide comprehensive and crucial insights into OAM transport and establish an ultrafast, contact-free approach for investigating OAM-to-charge conversion.
Comments28 pages, 5 figures
