Logo der Physikalisch-Technischen Bundesanstalt

Time Resolved Studies of Ultrafast Phenomena in Cooperative Condensed-Matter Systems

Kolloquium der Abteilung 2

Time resolved measurements provide a detailed insight into the dynamical properties of matter. The basic experimental concept of such measurements, the so-called pump-probe scheme, involves exciting a material with the pump pulse and observing the subsequent dynamical properties of a material with a second pulse, the probe, as a function of the variable time delay between pump and probe. The first part of the talk reports on time-resolved terahertz (THz) time-domain spectroscopy in high temperature (high-Tc) superconductors. Here, THz pump and THz probe pulses were used to explore the nonlinearity of the Josephson plasma in the high-Tc superconductor La1.84Sr0.16CuO4. The experimental results demonstrate that large amplitude THz pump field renders the superconductor transparent over a narrow frequency range, an effect similar to the light-induced transparency in nonlinear optics, even though the physical mechanism is substantially different. The second part of the talk presents results of time resolved x-ray diffraction experiments in the laser excited diluted magnetic semiconductor Ga0.91Mn0.09As. X-ray diffraction can directly observe small shifts in interatomic distance associated with lattice vibrations. These measurements show that in diluted magnetic semiconductors with randomly distributed magnetic impurities, spin-phonon interaction affects significantly the long wavelength acoustic vibrational modes by destroying their harmonic displacement pattern and quasilocalizing them in real space.