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O: Fachverband Oberflächenphysik

O 42: Focus Session: Frontiers of Electronic-Structure Theory – Advances in Time-Dependent and Nonequilibrium Ab Initio Methods III

O 42.2: Talk

Wednesday, March 20, 2024, 10:45–11:00, HE 101

Photoemission tomography of excitons in periodic systems through Wannier interpolation — •Christian Simon Kern and Peter Puschnig — Institute of Physics, NAWI Graz, University of Graz, Austria

Excitons, bound optical excitations below the band gap of a material, are theoretically described as correlated electron-hole states. Their wave functions can be obtained by many-body perturbation theory in the framework of the Bethe-Salpeter equation or within time-dependent density functional theory. Experimentally, time- and angular-resolved photoemission spectroscopy (t-ARPES) is arguably the most direct method to measure the excitons' momentum-space signatures, which is also boosted by the recent developments in ultra-fast laser physics.

For molecules in the gas-phase, a formal connection of the theoretical exciton wave function with measured t-ARPES momentum maps in the spirit of photoemission orbital tomography was recently established [1] and has lead to interesting consequences for t-ARPES: the photoemission signature of an exciton is measured at all kinetic energies that are in accordance with the energy conservation from its hole contributions, while the respective momentum maps result from a coherent sum over all electronic contributions. Here, we extend this formalism to periodic systems and momentum-dark excitons, which allows for the simulation of photoemission from excitons in crystals, van der Waals hetero-structures or metal-organic interfaces.

[1] C. S. Kern et. al., Phys. Rev. B 108, 085132 (2023).

Keywords: Excitons; time-dependent density functional theory; Bethe-Salpeter equation; Wannier functions; time-resolved photoemission spectroscopy