We present femtosecond time-resolved measurements of the dielectric tensor of tellurium following intense photoexcitation. Strong impulsive photoexcitation of crystalline tellurium weakens the covalent bonds between atoms, which undergo coherent oscillations (at $>3\mathrm{}$ THz) as they relax to new equilibrium positions. As this photoexcitation drives the lattice toward a band-crossing transition, we track the decrease and oscillation of the bonding-antibonding splitting. The reduction of the bonding-antibonding splitting exceeds the band gap for 100 fs, indicating a transient state with crossed bands.

• Received 30 April 2003

DOI:https://doi.org/10.1103/PhysRevB.68.012301