Layer and orbital interference effects in photoemission from transition metal dichalcogenides

TL;DR

This paper develops an effective model to analyze interference effects in photoemission from monolayer and bilayer transition metal dichalcogenides, revealing how orbital and layer interactions influence photoemission intensity and optical excitation.

Contribution

It introduces a $oldsymbol{k} oldsymbol{ullet} oldsymbol{p}$ Hamiltonian-based approach to quantify interference effects in photoemission and optical responses of MoS$_2$ layers, highlighting layer and orbital interference phenomena.

Findings

Interference effects cause significant masking of photoemission intensity outside the first Brillouin zone.

Inter-layer interference modulates photoemission intensity with photon energy in bilayer MoS$_2$.

Optical excitation induces momentum-dependent conduction band populations, leading to observable dichroism.

Abstract

In this work, we provide an effective model to evaluate the one-electron dipole matrix elements governing optical excitations and the photoemission process of single-layer (SL) and bilayer (BL) transition metal dichalcogenides. By utilizing a $\vec{k} \cdot \vec{p}$ Hamiltonian, we calculate the photoemission intensity as observed in angle-resolved photoemission from the valence bands around the $\bar{K}$-valley of MoS$_2$. In SL MoS$_2$ we find a significant masking of intensity outside the first Brillouin zone, which originates from an in-plane interference effect between photoelectrons emitted from the Mo $d$ orbitals. In BL MoS$_2$ an additional inter-layer interference effect leads to a distinctive modulation of intensity with photon energy. Finally, we use the semiconductor Bloch equations to model the optical excitation in a time- and angle-resolved pump-probe photoemission experiment. We find that the momentum dependence of an optically excited population in the conduction band leads to an observable dichroism in both SL and BL MoS$_2$.