Abstract
We show that ultrafast electron diffuse (inelastic) scattering provides a detailed, momentum-resolved view of electron-phonon and phonon-phonon coupling across the entire Brillouin zone. Ultrafast time-resolution and scattering selection rules can distinguish between phonon branches without energy-resolution.
Highlights
The nature of the couplings within and between lattice and charge degrees of freedom is central to condensed matter and materials physics
The dramatic changes reflect the non-equilibrium phonon populations and their time dependence. a) Raw diffraction pattern of graphite along the [001] zone axis. b) Differential scattering flat-field ∆I(q, τ) at a time before optical excitation. c) ∆I(q, 0.5 ps) provides a map of the relative strength of the q-dependent EPC coupling through the increased occupancy of strongly-coupled modes. d) Non-equilibrium phonon dynamics: relaxation of the transient population of strongly-coupled modes into mid-Brillouin zone acoustic modes e)
If only one mode contributes than its individual population dynamics can be observed directly even without energy resolution
Summary
The nature of the couplings within and between lattice and charge degrees of freedom is central to condensed matter and materials physics. Ultrafast electron diffuse scattering (UEDS) provides the answer. The information UEDS provides is analogous to time-resolved, angle resolved photoelectron spectroscopy (TR-ARPES) but for the phonon system rather than the electron system.
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