Quantized exciton-exciton annihilation in monolayer WS2 on SrTiO3 substrates with atomically flat terraces

TL;DR

This study investigates how substrate surface flatness influences exciton-exciton annihilation in monolayer WS2, revealing that atomically flat substrates require a quantum model for accurate description, aligning with encapsulated samples.

Contribution

The paper introduces a quantized EEA model to accurately describe exciton dynamics on atomically flat substrates, improving understanding of substrate effects on monolayer WS2.

Findings

Flat-terrace substrates show reduced EEA rates.

Conventional models are insufficient for flat substrates.

Quantized EEA model aligns with encapsulated WS2 results.

Abstract

Monolayer materials are strongly affected by their potential fluctuations, which are induced by an intrinsic corrugation or the surface roughness of the substrate. We compare the effective exciton-exciton annihilation (EEA) rate constants of monolayer WS2 on substrates with different surface topographies. We show that monolayer WS2 on the substrate with atomically flat terraces displays small effective EEA rate constant deviating from the overall tendency and multiple exciton decay components, which cannot be accounted for by a conventional EEA model. To obtain a correct description, we use a quantized EEA model. The intrinsic EEA rate constant for the flat-terrace substrates determined by this new model is comparable to that of hBN-encapsulated monolayer WS2.