Illustration: Alan Stonebraker

Figure 1: To observe the dynamics of electrons and phonons in a high-$Tc$ superconductor, Pashkin et al. used a pump-probe technique. (Top) The first laser pulse excites an electron above the superconducting gap, while a second pulse in the $THz$ range, reflected from the sample at variable delay $τ$, probes the gap. As time progresses, the superconducting gap closes and then opens again as indicated in the $THz$ reflectivity. (Bottom) Simultaneously with the electron excitation, lattice vibrations of oxygen atoms in the YBCO are probed by watching how the center frequency and asymmetry of the line shape of the reflected light changes with time. Surprisingly, the electrons and photons are excited and decay on the same time scale, suggesting that the dynamics of the two species are to some degree independent.