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Photoinduced insulator-metal transition from the charge-density wave (CDW) ground state in a onedimensional electron system is studied within the nonadiabatic theory of electron-phonon coupling. Ultrafast melting and partial recovery of the CDW and its critical slowing down are found to accompany the cooperative lattice response by an electron-phonon energy transfer on the subpicosecond time scale, which is read out by the nonadiabatic depopulation and repopulation of coherent phonons. Further, electron correlation is described in a self-consistent mean-field theory. In the strong electron correlation, the spin-density wave competes with the CDW and the photoinduced responses of the lattice is found to undergo the nonadiabatic-adiabatic transition.

We study the photoinduced nonequilibrium dynamics of a one-dimensional quarter-filled organic salt. Cooperative onsets of charge-order melting and coherent phonon generation are found in the early stage to ϳ ex ͑where ex : the pulse length of the pumping laser͒, which signifies that they are mutually driven. Later, at տ ex , there is nonadiabatic decoupling of the charge-order melting and coherent phonon generation. Calculation of optical conductivity and time-resolved photoemission spectra at տ ex is consistent with the recent experimental observations, which confirms a nonadiabatic charge-phonon interaction in the ultrafast time span.

The low-energy quasiparticle (QP) dynamics of graphite are governed by a coupling with the E(2g) longitudinal optical phonon of omega(LO) approximately 200 meV, which is found to dramatically depend on the electronic band dispersion epsilon(k). A discontinuity of the QP linewidth develops near omega(LO) for a linear band with a quadratic band top [near the Brillouin zone (BZ) K point], while it disappears for a pure linear band (near the BZ H point). It is also found that the effective electron-phonon coupling near the K point is stronger than near the H point by more than 50%. This finding makes possible a consistent understanding of recent angle-resolved photoemission observations near the K point.