Breakdown of the static dielectric screening approximation of Coulomb interactions in atomically thin semiconductors

TL;DR

This paper reveals that static dielectric screening models are insufficient for atomically thin semiconductors, showing that dynamical effects cause unexpected exciton blueshifts, which impacts the control of quantum states in layered materials.

Contribution

It demonstrates the breakdown of static dielectric screening approximation and introduces a dynamical screening model to better understand exciton behavior in 2D materials.

Findings

Exciton resonance blueshift exceeds 30 meV in high dielectric environments.

Static dielectric response mainly controls exciton binding energy.

High-frequency response dominates exciton self-energy effects.

Abstract

Coulomb interactions in atomically thin materials are uniquely sensitive to variations in the dielectric screening of the environment, which can be used to control quasiparticles and exotic quantum many-body phases. A static approximation of the dielectric response, where increased dielectric screening is predicted to cause an energy redshift of the exciton resonance, has been until now sufficient. Here, we use charge-tunable exciton resonances to study screening effects in transition metal dichalcogenide monolayers embedded in materials with dielectric constants ranging from 4 to more than 1000. In contrast to expectations, we observe a blueshift of the exciton resonance exceeding 30 meV for larger dielectric constant environments. By employing a dynamical screening model, we find that while the exciton binding energy remains mostly controlled by the static dielectric response, the exciton self-energy is dominated by the high-frequency response. Dielectrics with markedly different static and high-frequency screening enable the selective addressing of distinct many-body effects in layered materials and their heterostructures, expanding the tunability range and offering new routes to detect and control correlated quantum many-body states and to design optoelectronic and quantum devices.