Ultrafast Electron Diffuse Scattering And Its Application To 2d Materials

"The nature of the couplings within and between lattice and charge degrees of freedom is central to condensed matter and materials physics. Despite their fundamental role, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon couplings across all momenta has proved elusive. Ultrafast electron diffuse scattering provides the answer by measuring momentum-dependent phonon population dynamics similar to how time and angle resolved photoemission spectroscopy views the momentum-dependent occupation dynamics of electronic states. This method proves particularly effective in the study of 2D materials. A sophisticated analysis applied to ultrafast electron scattering measurements of graphite, follows the cascade of electron-phonon and phonon-phonon couplings after pulsed laser excitation in this well studied benchmark system. In a similar experiment on titanium diselenide, electronphonon coupling is measured by observing the effect of photoexcitation on the renormalized phonon frequencies with the characteristic momentum of titanium diselenide's charge density wave transition. Through its sensitivity to transient phonon occupancies and frequencies, ultrafast electron diffuse scattering is a novel and powerful method to unravel the physics of complex phases and properties determined through interplay between the electron and lattice systems." --