Attoclocking delocalized Bloch electrons with multi-terahertz fields

We use multi-terahertz (THz) light fields to force electron–hole pairs in crystalline semiconductors onto closed trajectories and clock the delay between separation and recollision with a 300 as precision. This value corresponds to 0.7% of the driving field’s oscillation period. The strong Coulomb correlations emergent in atomically thin WSe
2
are found to shift the optimal timing of recollisions by up to 1.2 ± 0.3 fs compared to the bulk material. A quantitative analysis with quantum-dynamic many-body computations yields a direct and intuitive view on how the Coulomb interaction, non-classical aspects, the strength of the driving field, and the valley polarization influence the dynamics, opening unprecedented views of quantum many-body correlations and phase transitions.