Exciton g factors of van der Waals heterostructures from first-principles calculations

Abstract

External fields are a powerful tool to probe optical excitations in a material. The linear energy shift of an excitation in a magnetic field is quantified by its effective g factor. Here we show how exciton g factors and their sign can be determined by converged first-principles calculations. We apply the method to monolayer excitons in semiconducting transition metal dichalcogenides and to interlayer excitons in MoSe 2 /WSe 2 heterobilayers and obtain good agreement with recent experimental data. The precision of our method allows us to assign measured g factors of optical peaks to specific transitions in the band structure and also to specific regions of the samples. This revealed the nature of various, previously measured interlayer exciton peaks. We further show that, due to specific optical selection rules, g factors in van der Waals heterostructures are strongly spinand stacking-dependent. The calculation of orbital angular momenta requires the summation over hundreds of bands, indicating that for the considered two-dimensional materials the basis set size is a critical numerical issue. The presented approach can potentially be applied to a wide variety of semiconductors.

Anisotropic optical properties of GeS investigated by optical absorption and photoreflectance

“…It is worth noting that the matrix elements calculated with the present methods have been shown to properly reproduce the relative PL intensity of TMDCs. 64 Hence, these values are expected to describe well the anisotropic properties of GeS. From the table, excellent agreement is found between the theoretical and experimental polarization directions and polarization degree, which further supports the assignation proposed here.…”

Highly energy-tunable quantum light from moiré-trapped excitons

“…Figure 1B shows an optical micrograph of the fabricated device. As determined by the cleaved edges of MoSe 2 and WSe 2 , the bright IX intensity, and Landé g-factors described below, the twist angles for the heterobilayer samples that we investigate are close to 60° (30). Graphite layers, which form the top and bottom gates of the heterobilayer, were connected to prepatterned Au electrodes.…”

Exciton g-factors in monolayer and bilayer WSe2 from experiment and theory

“…Note: During the submission of our manuscript, we became aware of three related works on the theory of exciton g-factors in TMD MLs and heterostructures from first principles [48][49][50] .…”