<p>Pulsed laser technologies have been revealing ultrafast phenomena in pico- and femto-second ranges. Combining scanning tunneling microscopy (STM), atomic-scale dynamics has been extensively studied. Two types of time-resolved STM have been performed which utilizes non-linear optical supportively [1-3] and light-field-driven bias modulation [4-6]. The light-field-driven STM has an advantage to measure density of states of electrons in scanning tunneling spectroscopy (STS) [5]. Subcycle (less than monocycle) terahertz (THz) field has been used to modulate bias voltage so that the temporal resolution of around 1 pico-seconds. Here, we developed light-field-driven STM using subcycle mid-infrared (MIR) pulses with the center frequency of 30 THz to reveal photo-induced atomic-scale dynamics in femtosecond range.</p><p>A laser source of optical parametric chirped pulse amplifier (OPCPA) with the pulse duration of 8.2 fs was used to generate subcycle MIR pulses using a nonlinear crystal of GaSe. Time-resolved STM was conducted by using near-infrared (NIR) pump pulses as shown in Fig. 1(a) which induces interband transition in a layered compound of MoTe₂. Ultrafast modulation of the tunneling current as shown in Fig. 1(b) was succeeded to be measured with the scale of 29 fs which is considered to be contributed by hot-electrons. This technique will pave a new way for studying non-equilibrium electrons in atomic scale. Combining other pump conditions and detection schemes, unambiguous understanding of surface dynamics can be expected [2, 3, 8].</p><p></p><p>[1] S. Liu et al., Sci. Adv. 8, 5682 (2022). [2] H. Mogi et al., npj 2D Mat. Appl. 6,72 (2022). [3] H. Mogi, et al., Jpn. J. Appl. Phys. 61, SL1011 (2022). [4] T. L. Cocker, et al., Nat. Photon. 7, 620 (2013). [5] S. Yoshida et al., ACS Photon. 6, 1356 (2019). [6] S. Yoshida et al., ACS Photon. 8, 315 (2021). [7] Y. Arashida et al., ACS Photon. 9, 3156 (2022). [8] Y. Arashida et al., Appl. Phys. Exp. 15, 092006 (2022).</p>