Ultrafast relaxation in YBa2Cu3O7−δ on the femtosecond scale: Luttinger or two-dimensional Fermi liquid picture?

A method for probing Fermi liquid (FL) versus non-Fermi liquid (NFL) behavior in the normal state of high Tc oxide-superconductors YBa2Cu3O7−δ by femtosecond pump-supercontinuum probe spectroscopy is presented. The method is based on the determination of the spectral dependence of non-equilibrium charge carriers relaxation rate γ(ωprobe) in a wide spectral range of probing, ℏωprobe=1.6–3.2 eV. It is shown that the relaxation rate decreases sharply for the optical transitions in the vicinity of the Fermi level EF, the position of the rate minimum pointing to the location of EF. The probe energy dependence of the relaxation rate around the minimum gives unique information on the damping rate of quasi-particles near the Fermi level and hence can resolve the FL versus NFL behavior. Deviations from the FL behavior in YBa2Cu3O7−δ are observed and discussed.