Transient Bose-Einstein condensation of phonons

We report on the first observation of non-equilibrium quantum condensate for the A1g coherent phonons in a single crystal of bismuth. The condensation was achieved at 7 K by employing the high intensity ultrashort pulses. The similarities to Bose-Einstein condensation include the degenerate macroscopically occupied phonon state, the emergence, above critical laser fluence, of collapse and revival, and the spectrum renormalization. (C) 2004 Elsevier B.V. All rights reserved.