RESUMO
Photo-control of material properties on femto- (10(-15)) and pico- (10(-12)) second timescales at room temperature has been a long-sought goal of materials science. Here we demonstrate a unique ultrafast conversion between the metallic and insulating state and the emergence of a hidden insulating state by tuning the carrier coherence in a wide temperature range in the two-leg ladder superconductor Sr(14-x)Ca(x)Cu24O41 through femtosecond time-resolved reflection spectroscopy. We also propose a theoretical scenario that can explain the experimental results. The calculations indicate that the holes injected by the ultrashort light reduce the coherence among the inherent hole pairs and result in suppression of conductivity, which is opposite to the conventional photocarrier-doping mechanism. By using trains of ultrashort laser pulses, we successively tune the carrier coherence to within 1 picosecond. Control of hole-pair coherence is shown to be a realistic strategy for tuning the electronic state on ultrafast timescales at room temperature.
RESUMO
Forward and backward stimulated Raman scattering (SRS) of OH stretching vibrations are measured when an intense 40 ps pulsed beam is focused into water. Characteristic features related to the interaction of OH groups with excess electrons generated by the strong laser irradiation are observed. The SRS spectra are indicative of the important role which excess electrons play in transient enhancement of the SRS at the initial stage of laser-induced plasma generation in water. The hydration structures around the excess electrons in water are also discussed.
