Photoinduced changes in the cuprate electronic structure revealed by femtosecond time- and angle-resolved photoemission

The dressing of quasiparticles in solids is investigated by changes in the electronic structure E(k) driven by femtosecond laser pulses. Employing time-and angle-resolved photoemission on an optimally doped cuprate above T-c, we observe two effects with different characteristic temporal evolutions and, therefore, different microscopic origins. First, a marked change in the effective mass due to the 70-meV kink in E(k) is found to occur during the experiment's 100-fs temporal resolution and is assigned to laser-driven perturbation of an electronic interaction dressing the bare band. Second, a change in k(F) is explained by effective photodoping due to particle-hole asymmetry and offers opportunities for ultrafast optoelectronic switches based on an optically driven insulator-superconductor transition.