Dynamics and mean-free path of electronic excitations in WSe_2

摘要

The anisotropy of the quasiparticle lifetime in the layered tungsten dichalcogenide WSe2is studied for energies up to 90 eV above the Fermi level. The inverse lifetime is calculated within theGWapproximation based on a full energy and momentum dependentab initiodielectric function of WSe2and wave functions calculated by the plane wave pseudopotential method. The relation between the energy loss function and the quasiparticle lifetime is analyzed. The electron mean free path for three propagation directions ΓA, ΓK, and ΓM was obtained by including the inverse lifetime as an absorbing potential into the Schrödinger equation and calculating the electron scattering by the surface. The inverse quasiparticle lifetime is found to grow steadily and smoothly with energy, and, in spite of the highly anisotropic geometry, to be very similar for the three directions. At the same time, the mean free path is found to vary non-monotonically with energy and to show significant anisotropy.