Charge-Density-Wave-Induced Modifications to the Quasiparticle Self-Energy in 2H-TaSe2

The self-energy of the photohole in $2\mathrm{H}-{\mathrm{TaSe}}_2$ is measured by angle-resolved photoemission spectroscopy as a function of binding energy and temperature. In the charge-density wave (CDW) state, a structure in the self-energy is detected at $\sim 65\mathrm{meV}$ that cannot be explained by electron-phonon scattering. A reduction in the scattering rates below this energy indicates the collapse of a major scattering channel with the formation of the CDW state accompanying the appearance of a bosonic “mode” in the excitation spectrum of the system.