Resonance-enhanced excitation and relaxation dynamics of coherent phonons in FeTe.

Lattice dynamics plays a significant role in manipulating the unique physical properties of materials. In this work, femtosecond transient optical spectroscopy is used to investigate the generation mechanism and relaxation dynamics of coherent phonons in FeTe-a parent compound of chalcogenide superconductors. The reflectivity time series consist of the exponential decay component due to hot carriers and damped oscillations caused by the A phonon vibration. The vibrational frequency and dephasing time of the A phonons are obtained as a function of temperature. With increasing temperature, the phonon frequency decreases and can be well described with the anharmonicity model. Dephasing time is independent of temperature, indicating that the phonon dephasing is dominated by phonon-defect scattering. The impulsive stimulated Raman scattering mechanism is responsible for the coherent phonon generation. Owing to the resonance Raman effect, the maximum photosusceptibility of the A phonons occurs at 1.590 eV, corresponding to an electronic transition in FeTe.