Atomic-scale ultrafast dynamics of local charge order in a THz-induced metastable state of 1T-TaS2

Abstract: Light-induced control of quantum materials enables manipulation of electronic and structural phases on ultrafast timescales. Probing their atomic-scale dynamics is essential to understand the role of defects and domain boundaries, but conventional time-resolved techniques lack the required spatial resolution. Here, we use terahertz (THz) scanning tunneling microscopy to investigate a THz-light-induced metastable state near a defect in 1T-TaS2, and follow its photoinduced dynamics in real space and time. THz excitation induces quasi-stationary changes in the insulating gap on angstrom scales, which we associate with interlayer stacking changes. Simultaneously, THz-lightwave-driven tunneling provides access to ultrafast dynamics of the metastable state, revealing 2.5 THz oscillations of the charge density wave amplitude mode and a 1.3 THz mode attributed to an interlayer shear vibration emerging near the defect. Our results demonstrate the dual role of tip-enhanced THz fields in driving metastability and ultrafast tunneling, opening new avenues for ultrafast atomic-scale control of quantum materials.