Abstract

Detailed investigations of coherent phonons in high temperature superconductors are presented. They are synchronously launched in YBa₂CU₃O₇-films by excitation with 50 fs laser pulses at 2 eV and detected at the same photon energy through periodic modulation of the reflectivity signature. As shown in fig. 1 the positive reflectivity change at room temperature decays with at least two time constants. The positive dR/R_O change indicates that the Fermi level of YBa₂Cu₃O₇ lies above the excited states. Below the transition temperature the dynamics and sign of the reflectivity change indicate the excitation and relaxation of quasiparticles.

© 1992 The Author(s)