THz-driven scanning tunneling-induced luminescence: a brief review

Terahertz-lightwave-driven scanning tunneling microscopy (THz-STM) enables femtosecond control of tunneling currents by transiently gating the junction bias with single-cycle THz pulses. STM-induced luminescence (STML), on the other hand, provides spectrally resolved optical access to locally excited states and their radiative decay within the tunneling junction. Terahertz-driven STML (THz-STML) combines these approaches by uniting ultrafast bias modulation with photon detection, enabling probing of tunneling-induced excited states and their ultrafast dynamics with simultaneous atomic spatial and femtosecond temporal resolution. By correlating femtosecond tunneling-induced excitations and charge injection with light emission, THz-STML enables ultrafast control over excited-state formation in individual quantum systems and provides insight into their relaxation pathways and radiative decay under non-equilibrium conditions. In this concise review, we outline the fundamental physical principles and experimental challenges of THz-STML, summarize recent advances, and highlight emerging opportunities for ultrafast optical spectroscopy in STM junctions.