Origin of the quasiparticle dispersion kinks in Bi-2212 determined from angle-resolved inelastic electron scattering

The kink features in the low energy quasiparticle dispersion in cuprate superconductors have been extensively studied using angle-resolved photoemission spectroscopy (ARPES). The existence of these kinks is a signature of a renormalization of the fermionic quasiparticles due to coupling to some bosonic collective mode at a scale related to the kink energy. In this talk, I will present angle-resolved inelastic electron scattering studies of the bosonic collective excitations in optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. Performing a 2D momentum parameterization of these modes, we reconstruct the complete dynamical susceptibility, $\chi(q,\omega)$, which we use to perform a one-loop self energy correction to the quasiparticle dispersion. The result reproduces well the dispersion observed with ARPES, indicating that these excitations are the origin of the observed kinks. I will discuss the implications of our study for phonon vs.\ spin fluctuation interpretation of these effects.