Fano interference for large-amplitude coherent phonons in bismuth

We report femtosecond time-resolved measurements of lattice dynamics in bismuth made over a wide range of temperatures and excitation levels. We demonstrate that time-integrated Fourier transforms for both the fully symmetric A(1g) and doubly degenerate E-g coherent oscillations of large amplitude exhibit asymmetric line shapes described by the Fano formula. Measuring the real and imaginary part of the phonon self-energy, we attempt to identify the nature of the continuum responsible for the configuration mixing. Based on the measured pump and temperature dependences, we suggest that the continuum responsible for the interference includes both the electronic and lattice degrees of freedom.