New method of non-Fermi liquid study by pump-supercontinuum probe femtosecond spectroscopy

A new method of investigation for the Fermi surface and Fermi liquid (FL) versus non-Fermi liquid (NFL) behavior in strongly correlated electron systems by femtosecond laser spectroscopy is proposed. The method consists in the study of the spectral dependence of the nonequilibrium charge carrier relaxation time by the pump-supercontinuum probe technique. This method is demonstrated on the high Tc oxide-superconductor YBa2Cu3O7−δ by studying the temporary changes of the optical density of a YBa2Cu3O7−δ thin film in a wide spectral region of probing h̷ωprobe = 1.6–3.0 eV. The relaxation time sharply grows in the spectral area, related to optical transitions in the vicinity of the Fermi level (or its shadow). The position of this peak gives the location of the Fermi surface (FS). The form of the peak gives unique information on the damping rate near the FS and thus on the FL versus NFL behavior.