Atomically resolved terahertz scanning tunneling spectroscopy as a tool for exploring new materials*

Lightwave-driven scanning tunnelling microscopy achieves exquisite spatio-temporal resolution through coherent control of tunnel currents with the oscillating field of a single-cycle light pulse. It was first demonstrated at terahertz frequencies [1], which are particularly well suited to such strong-field control [2,3]. Terahertz scanning tunnelling microscopy (THz-STM) has subsequently been used to resolve the picosecond motion of single molecules [4-6] and extreme tunnel currents through single silicon atoms [7], among other exciting recent results [3]. Thanks to its combination of ultrafast temporal resolution with atomic spatial resolution, THz-STM promises further breakthroughs, especially as a tool for exploring new materials. Yet, its unique view also necessitates a deep understanding of how THz-STM measurements relate to the underlying physics of the system, as the phenomena in question may not be visible to any other experimental technique. Here, we establish an experimental [8] and theoretical [9] framework for atomically resolved terahertz scanning tunnelling spectroscopy, which we believe will be a key modality for future studies.

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