Order and strain dynamics during electrical melting of charge density waves in TaS₂ 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.