Ultrafast Exciton Formation in a Molecule by Terahertz-field-driven Electron Tunneling

We reported ultrafast exciton formation in a single molecule induced by terahertz (THz) field–driven electron tunneling in a scanning tunneling microscope (STM). By combining THz-STM with scanning tunneling luminescence spectroscopy (THz-STL), we directly probed that the exciton was formed by sequential and state-selective electron tunneling within a single-cycle THz pulse. Furthermore, by employing THz pulse pairs with controlled delay, we achieved ultrafast control of exciton formation on the picosecond timescale. These results established THz-STL as a powerful platform for investigating and controlling ultrafast charge and exciton dynamics at the single-molecule level.