Mott transition in Cr-doped V₂O₃ studied by ultrafast reflectivity: Electron correlation effects on the transient response

¹ Laboratoire de Physique des Solides, CNRS-UMR 8502, Université Paris-Sud - F-91405 Orsay, France, EU
² Laboratoire d'Optique Appliquée, ENSTA, CNRS, Ecole Polytechnique - F-91761 Palaiseau, France, EU
³ Institut d'Electronique Fondamentale, CNRS-UMR 8622, Université Paris-Sud - F-91405 Orsay, France, EU

Received: 13 August 2010
Accepted: 22 October 2010

Abstract

The ultrafast response of the prototype Mott-Hubbard system (V_1−xCr_x)₂O₃ was systematically studied with fs pump-probe reflectivity, allowing us to clearly identify the effects of the metal-insulator transition on the transient response. The isostructural nature of the phase transition in this material made it possible to follow across the phase diagram the behaviour of the detected coherent acoustic wave, whose average value and lifetime depend on the thermodynamic phase and on the correlated electron density of states. It is also shown how coherent lattice oscillations can play an important role in some changes affecting the ultrafast electronic peak relaxation at the phase transition, changes which should not be mistakenly attributed to genuine electronic effects. These results clearly show that a thorough understanding of the ultrafast response of the material over several tenths of ps is necessary to correctly interpret its sub-ps excitation and relaxation regime, and appear to be of general interest also for other strongly correlated materials.