Andrea Cavalleri

Abstract:

An ultrafast electronic phase transition, associated with melting of orbital order, is driven in La1/2Sr3/2MnO4 by selectively exciting the Mn-O stretching mode with femtosecond pulses at 16 microm wavelength. The energy coupled into this vibration is less than 1% of that necessary to induce the transition thermally. Nonthermal melting of this electronic phase originates from coherent lattice displacements comparable to the static Jahn-Teller distortion.

Abstract:

The initial dynamics of photo-induced phase transition in (EDO-TTF) 2PF6 was investigated using 10-fs laser pulses. We observed sub-20-fs gigantic photo-responses (|ΔR/R|>100%) and a clear signature of a structural bottleneck (∼60 fs) for the first time. © 2008 Optical Society of America.

Abstract:

We show that selective excitation of a phonon mode induces an insulator-metal phase transition in a magnetoresistive manganite. The dynamics of such phase transformation are studied by optical pump-probe, transport and X-ray absorption measurements. © 2008 Optical Society of America.

Abstract:

The transient nanoscale dynamics of materials on femtosecond to picosecond timescales is of great interest in the study of condensed phase dynamics such as crack formation, phase separation and nucleation, and rapid fluctuations in the liquid state or in biologically relevant environments. The ability to take images in a single shot is the key to studying non-repetitive behaviour mechanisms, a capability that is of great importance in many of these problems. Using coherent diffraction imaging with femtosecond X-ray free-electron-laser pulses we capture time-series snapshots of a solid as it evolves on the ultrafast timescale. Artificial structures imprinted on a Si 3 N 4 window are excited with an optical laser and undergo laser ablation, which is imaged with a spatial resolution of 50nm and a temporal resolution of 10ps. By using the shortest available free-electron-laser wavelengths and proven synchronization methods this technique could be extended to spatial resolutions of a few nanometres and temporal resolutions of a few tens of femtoseconds. This experiment opens the door to a new regime of time-resolved experiments in mesoscopic dynamics. © 2008 Macmillan Publishers Limited. All rights reserved.