Barbara Mansart, LPEM

Jeudi 02 Octobre 2014, 14h
Amphi Holweck, Esc C, 1ème etage

Ultrafast studies and coherent oscillations in the Mott compound V2O3 and the
high-Tc superconductor La2-xSrxCuO4.

Barbara Mansart

Time-resolved spectroscopies allow the coherent excitation and real-time observation of atomic motions and elementary electronic excitations, which are important fingerprints of the excited system physical properties and can be used for shining new light on the phase diagram of strongly correlated materials.
In the prototype Mott compound V2O3, where the metal-insulator transition occurs due to the presence of strong electronic repulsion, ultrafast light pulses photoinduce a strong transient hardening revealed by a 14% blue-shift of the coherent A1g phonon mode. The effect is controlled by a transfer of electrons to the bonding a1g orbital, and produces a lattice configuration which is in stark contrast with the thermally accessible ones. These results unveil new opportunities for the ultrafast control of material parameters, and are of particular relevance for the optical manipulation of strongly correlated materials [1].
In the high-Tc superconductor La2-xSrxCuO4 (x=0.15), the coherent oscillations of the
Cooper pairs condensate has been detected via delayed supercontinuum pulses for the first time. Using coherent charge fluctuation spectroscopy, the electronic excitations that couple to the superconducting quasiparticles is distinguished. These results reveal strong resonance effects between the oscillating condensate and high energy electronic transitions attributed to the Cu-O charge transfer excitation, suggesting the importance of non-retarded interactions in the superconductivity mechanism of cuprates [2].

[1] B. Mansart, D. Grieger, D. Boschetto, G. Lantz, V. Balédent, N. Moisan, E. Papalazarou, A. Savoia, M. Fabrizio and M. Marsi, "Ultrafast photo-induced non-thermal phonon hardening in the Mott compound V2O3", submitted.

[2] B. Mansart, J. Lorenzana, A. Mann, A. Odeh, M. Scarongella, M. Chergui and F. Carbone, "Coupling of a high-energy excitation to superconducting quasiparticles in a cuprate from coherent charge fluctuation spectroscopy.", Proc. Natl. Acad. Sci. USA 110, 4539 (2013).

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