Advances in light sources and time resolved spectroscopy have made it
possible to excite specific atomic vibrations in solids and to observe the
resulting changes in electronic properties. I argue that in narrow-band
systems the dominant symmetry-allowed coupling between electron density
and dipole active modes implies an electron density-dependent squeezing of
the phonon state which provides an attractive contribution to the electron-electron
interaction, independent of the sign of the bare electron-phonon
coupling and with a magnitude proportional to the degree of laser-induced
phonon excitation. Reasonable excitation amplitudes lead to non-negligible
attractive interactions that may cause significant transient changes in
electronic properties including superconductivity. The mechanism is
generically applicable to a wide range of systems, offering a promising route
to manipulating and controlling electronic phase behavior in novel materials.
