A femtosecond multi-terahertz view of the phonon and quasiparticle dynamics in superconducting YBa2Cu3O7-δ

We probe the mid-infrared conductivity of YBa₂Cu₃O_7-δ parallel and perpendicular to the CuO₂ planes after 12-fs optical excitation. Quasiparticle excitations and specific lattice modes are traced simultaneously during the photoinduced non-thermal transition to the normal state. The condensate is completely destroyed within 150 fs, while characteristic phonon resonances undergo a blue-shift on distinctly slower times of up to 0.9 ps. The results indicate selective electron-phonon coupling and strong lattice anharmonicities.