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S. Brazovskii (LPTMS-CNRS, University Paris-Sud)
Nonequilibrium coherent dynamics in Charge Density Waves from femto-second optical experiments and their modeling.
Jeudi 20 Janvier 2011, 14h15
par- 10 décembre 2010
Problems in temporal evolution of symmetry breaking phase transitions span subjects from high energy and cosmology, to condensed matter. The reported new approach  is the optical study of a far-from-equilibrium evolution of the electronic charge ordering after a quench caused by an intense laser pulse. Technique of multi-pulse spectroscopy with a femto-second resolution allowed to simultaneously monitor both bosonic and fermionic components, coherent aperiodic undulations of the order parameter, critical slowing down of the collective mode (akin to the Higgs boson), and evolution of the particle-hole gap which is due to the Peierls-BCS mechanism. The numerical modeling with no fitting parameters allowed reproducing the observations, particularly the spatio-temporal distortions : "Higgs waves" arising from "earthquakes" - annihilation events of topological defects in depth of the sample. The results give a rare access to the in-situ dynamics of phase transitions.
We shall discuss also other manifestation of strong amplitude perturbations. At a local microscopic scale accessed by the STM, the amplitude solitons play a role of neutral spin carriers - spinons. Their aggregation into solitonic lattices gives rise to modulated phases in spin-polarised superconductors or Charge Density Waves.
 In collaboration with D. Mihailovic group at the Jozef Stefan Institute, Ljubljana, Slovenia. R. Yusupov, et al, ìCoherent dynamics of macroscopic electronic order through a symmetry breaking transitionî, Nature Physics, 2010
Brazovskii - 126.2 ko