Dynamic separation of electron excitation and lattice heating during the photoinduced melting of the periodic lattice distortion in 2H-TaSe2

Abstract

The photoinduced structural dynamics in 2H-TaSe2 in the charge-density wave (CDW) state is investigated using MeV ultrafast electron diffraction. By simultaneously tracking both the melting of the periodic lattice distortion (PLD) associated with the CDW and the lattice heating, following an impulsive photoexcitation, the separate contributions of electronic excitation and lattice thermalization to the melting process are disentangled in the time domain. Two distinct time-constants, reflecting the corresponding individual dynamics of the subsystems, are observed. Our experimental results demonstrate that the PLD in 2H-TaSe2 is first suppressed promptly by the electronic excitation and scattering, and then subsequently by lattice thermalization through electron-phonon interaction, on a much longer time scale. This latter leads to the final, full melting of the PLD.