报告题目：Nonequilibrium coherent dynamics in Charge Density Waves from femto-second optical experiments and their modeling

报 告 人：Serguei Brazovskii, Laboratoire de Physique Théorique et des Modèles Statistiques, CNRS,University Paris-Sud, Orsay, France

报告时间：11月24日下午2：30

报告地点：物理系三楼报告厅

报告摘要：Problems in temporal evolution of symmetry breaking phase transitions span subjects from high energy and cosmology, to condensed matter. The reported new approach [1] 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 in electronic systems. 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.

[1] R. Yusupov, et al, “Coherent dynamics of macroscopic electronic order through a symmetry breaking transition”, Nature Physics, 2010.