visualized by ultrafast electron microscopy*

Electrically induced transitions in charge density waves (CDWs) have proven valuable for understanding the underlying electron and lattice interactions as well as accessing novel transition pathways and non-equilibrium states. However, the transition mechanisms are often debated as electric field, current, carrier injection, heat, and strain can all contribute and play varying roles across length and time scales. I will present our recent experiments which visualize and disentangle these factors for transitions in the room temperature, nearly commensurate CDW state in 1T-TaS₂. We employed a unique, new ultrafast electron microscopy capability at the Center for Nanoscale Materials at Argonne National Laboratory to record atomic and mesoscopic structural dynamics during electrical pulse stimulation with nanosecond-nanometer spatiotemporal resolution. Recording the order parameter following voltage pulses down to 20 ns duration, we find the transition thresholds and dynamics are consistent with a self-heating mechanism, showing robustness to applied fields and injected currents. In addition, time-resolved imaging reveals heterogeneous strain dynamics, including emergence of coherent acoustic resonances for sub-100 ns pulses.