Ultrafast charge dynamics in photoexcited Nd2CuO4 and La2CuO4 cuprate compounds investigated by femtosecond absorption spectroscopy

Charge and lattice dynamics caused by photocarrier doping of the undoped cuprates Nd2CuO4 and La2CuO4 were studied by femtosecond absorption spectroscopy. In both compounds, a metallic state is formed just after photoexcitation and decays within similar to 200 fs. Photogenerated electrons and holes are subsequently localized due to charge-spin coupling, producing midgap absorptions at different energies. Charge-phonon coupling also occurs in both compounds. This is more significant for La2CuO4 than for Nd2CuO4, and leads to higher midgap absorption energies, and slower recombination of polaronic carriers. The role of apical oxygen atoms in charge-phonon coupling in La2CuO4 is also discussed.