FERMI GLASS CARRIER RELAXATION THROUGH THE ANDERSON TRANSITION IN YBA2CU3O7-DELTA INVESTIGATED BY ULTRAFAST RAMAN-SCATTERING

We report a microscopic investigation of carrier relaxation dynamics i n YBa2Cu3O7-delta. Electrons are excited out of equilibrium by 1.5 pic osecond laser pulses and their subsequent collisions with the lattice are investigated by counting - with the use of Stokes anti-Stokes Rama n scattering - the resulting non-equilibrium occupation numbers for di fferent lattice vibrations. The photoexcitation intensity is varied su ch that the system is driven through the Anderson transition. The elec tron-phonon scattering rate for both planar and out-of-plane phonons i s seen to decrease in the metallic state, the change being coincident with changes in dielectric constant and conductivity reported by Yu et al (Phys. Rev. B 45, 4964, (1691)). The temperature dependence of car rier-lattice interaction rather unambiguously implies Fermi-glass carr ier relaxation dynamics where carriers relax by hopping between locali zed states.