Seminar By Adrian E Feiguin, Northeastern University

Title: Beyond perturbation theory: multi-photon and non-radiative recombination effects in spectroscopies

Host: Kun Yang

Abstract: The conventional calculation of scattering cross sections relies on a treatment based on timedependent perturbation theory that provides formulation in terms of Green’s functions in the frequency domain. In equilibrium, it boils down to evaluating a simple spectral function equivalent to Fermi’s golden rule, which can be solved efficiently by a number of numerical methods. However, away from equilibrium, the resulting expressions require a full knowledge of the excitation spectrum and eigenvectors to account for all the possible allowed transitions and intermediate states, a seemingly unsurmountable complication. We have recently presented a new paradigm to overcome these hurdles[1-3]: we explicitly introduce the scattering particles (neutron, electron, photon, positron) and simulate the full scattering event by solving the time-dependent Schrödinger equation. The spectrum is recovered by measuring the momentum and energy lost by the scattered particles, akin an actual energy-loss experiment. I here show how these ideas can be generalized to study multi-photon processes such as coincidence ARPES, and the interplay between radiative and non-radiative recombination channels in X-ray spectroscopies.

References:

[1] Krissia Zawadzki, Luhang Yang, Adrian E. Feiguin; Phys. Rev. B 102, 235141 (2020).

[2] Krissia Zawadzki, Adrian Feiguin; Phys. Rev. B 100, 195124 (2019).

[3] Krissia Zawadski, Alberto Nocera, and Adrian E. Feiguin arXiv: 1905.08166