Fermi liquid study on femtosecond scale

The investigation of Fermi surface (FS) and Fermi liquid (FL) versus non-Fe rmi liquid (NFL) behavior in strongly correlated electron systems by femtos econd laser spectroscopy is presented. The method of the FS investigation i s based on the determination of the spectral dependence of nonequilibrium c harge carriers relaxation rate gamma((h) over bar omega(probe)) by femtosec ond pump-supercontinuum probe technique in a wide spectral region of probin g (h) over bar omega(probe) = 1.6-3.2 eV. The usefulness of this method is demonstrated on weakly correlated electron systems in Au and Cu and strongl y correlated electron system in high-T-c oxide-superconductor YBa2CU3O7-del ta. It is shown that the relaxation rate sharply slows down in the spectral region, related to the optical transitions into the vicinity of the Fermi level and the position of rate minimum gives the location of the FS. The ra te energy dependence around minimum gives a unique information on the quasi particles damping rate near the FS and thus on the FL vs. NFL behavior.