Lightwave-driven terahertz scanning tunnelling microscopy (THz-STM) is capable of exploring ultrafast dynamics across a wide range of materials with ångström resolution (10⁻¹⁰ m). In contrast to scanning near-field optical microscopy, where photons scattered by the tip apex are analysed to access the local dielectric function on the nanoscale, THz-STM uses a strong-field single-cycle terahertz pulse to drive an ultrafast current across a tunnel junction, thereby probing the local density of electronic states. Yet, the terahertz field in a THz-STM junction may also be spectrally modified by the local electromagnetic response of the sample. Here we demonstrate atomic-scale terahertz time-domain spectroscopy by combining waveform sampling with terahertz scanning tunnelling spectroscopy to study a single gallium arsenide surface defect, which exhibits a strongly localized terahertz resonance and resembles the elusive DX centre. These results are based on a generally applicable and self-consistent approach for terahertz near-field waveform acquisition in a tunnel junction that can distinguish local sample properties from effects due to terahertz pulse coupling, enabling comprehensive near-field microscopy on the atomic scale.

光波驱动的太赫兹扫描隧道显微镜（THz-STM）能够以埃级分辨率（10 ⁻¹⁰ m）探索各种材料的超快动力学。扫描近场光学显微镜通过分析尖端散射的光子来获取纳米级的局部介电函数，与之相反，太赫兹-STM 使用强场单周期太赫兹脉冲来驱动超快电流穿过隧道结，从而探测电子态的局部密度。然而，太赫兹-STM 结中的太赫兹场也可能会因样品的局部电磁响应而发生光谱改变。在这里，我们通过将波形采样与太赫兹扫描隧道光谱相结合来研究单个砷化镓表面缺陷，展示了原子级太赫兹时域光谱，该缺陷表现出强烈的局部太赫兹共振，并且类似于难以捉摸的 DX 中心。这些结果基于一种普遍适用且自洽的隧道结太赫兹近场波形采集方法，该方法可以区分局部样品特性与太赫兹脉冲耦合造成的影响，从而实现原子尺度的全面近场显微镜。