Ultrafast dynamics in optimally doped YBa₂Cu₃O_7-δ observed with white light pump-probe spectroscopy

The quasiparticle relaxation dynamics in optimally doped (001) YBa ₂Cu ₃O _7-δ thin films were measured at various temperatures by white light pump-probe technique. The 2D ultrafast spectroscopy with broadband (∼200 nm) and high time-resolution (∼9 fs) was performed by the non-collinear optical parametric amplifier (NOPA). The relaxation time and the amplitude of the transient transmissivity changes (ΔT/T) are wavelength-dependent. The maximum ΔT/T appears at around 625 nm (∼1.98 eV) which corresponds to the transition between the Fermi level and the UHB (upper Hubbard band). Furthermore, the oscillations with ∼150, ∼320, ∼500 cm ^-1 have been clearly observed in the Fourier transformed graph of the 2D ultrafast spectroscopy, which are consistent with the phonon modes in Raman-scattering spectra.