Dynamics, photoexcitation, and coherent anharmonicity in polyyne

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Abstract
Treating the infinite linear carbon chain, polyyne, as a Peierls-distorted metal at the half-filled-band level, we study its intrinsic defect states and adiabatic dynamics within a discrete tight-binding Hamiltonian. The qualitative validity of previously derived continuum results is confirmed numerically, effects of discreteness demonstrated, and the stability of the predicted kink and polaronlike states established. A continuum ansatz suggests that the kink has a maximum propagation velocity. This is confirmed numerically. The adiabatic dynamics of the discrete polyyne chain following one-electron and two-electron photoexcitation are studied numerically. The former study verifies the photoproduction of a polarexciton, while the latter study reveals that a kink-antikink pair and a dynamic optical-phonon packet—a breather—are photoproduced. The optical absorptions associated with the polarexciton and the breather are also numerically studied. A polarexciton with internal motion is found to absorb differently from a static polarexciton, illustrating the limitations of the adiabatic formalism for the optical absorption of dynamic structures.

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