Characterization of THz-induced bias voltage modulation in an STM

To understand and characterize the transient bias voltage induced by single-cycle terahertz (THz) pulses coupled to a scanning tunneling microscope (STM), the Bardeen tunneling model is applied to a 3-dimensional geometry of the STM junction. The simulated THz-induced tunneling current at the junction agrees well with that observed by THz-STM on a Cu(111) surface, providing a benchmark to quantify the THz-induced bias voltage at the tip-sample interface.