Stanford University / PULSE Institute

Recent inelastic neutron scattering measurements on lead telluride (PbTe) have rejuvenated interest in the fundamental phonon dynamics of the long-established and widely-used thermoelectric material. In particular, anomalous features in the TO phonon dispersion very near and moving away from zone center have led to speculation that effects such as strong anharmonic phonon coupling or local symmetry breaking might play a significant role in the phonon dynamics of PbTe and ultimately its naturally low thermal conductivity. We utilize a variety of ultrafast pump-probe techniques in order to investigate with fine time resolution the phonon dynamics of PbTe in a large region of reciprocal space. This includes work from a recent experiment using the XPP instrument at LCLS in which we employ an optical wavelength pump to excite phonons in the material and then probe with x-ray diffuse scattering captured by a large area detector in a technique called Fourier transform inelastic x-ray scattering (FT-IXS). The scheme provides us access to valuable time-domain data on the phonon activity of PbTe across several Brillouin zones simultaneously. As a result, we can extract dispersion curves with high momentum resolution and study in detail the shape and behavior of the curves. We discuss the potential implications of the collected data on both the electron-phonon and phonon-phonon interactions of PbTe and how this impacts the most recent discussion and understanding of PbTe phonon dynamics.