Temperature-dependent Optical and Polaritonic Properties of hBN-encapsulated Monolayer TMDs

TL;DR

This study comprehensively examines how temperature affects the optical and polaritonic properties of hBN-encapsulated monolayer TMDs, revealing material-specific responses and potential for optoelectronic applications.

Contribution

It provides the first detailed comparison of temperature-dependent optical and polaritonic behaviors of four high-quality monolayer TMDs encapsulated in hBN.

Findings

MoSe2 shows the strongest optical and polaritonic response.

All TMDs exhibit temperature-dependent negative permittivity supporting surface polaritons.

MoSe2 has enhanced polaritonic properties with narrower linewidths at low temperatures.

Abstract

Monolayer transition metal dichalcogenides (TMDs) support robust excitons in the visible to near-infrared spectral range. Their reduced dielectric screening results in large binding energies, and combined with a direct bandgap in monolayer form, these excitons dominate the optical response of TMDs. In this work, we present a comprehensive investigation of the temperature-dependent optical and polaritonic properties of high-quality, flux-grown $\mathrm{WS_2}$, $\mathrm{MoS_2}$, $\mathrm{WSe_2}$, and $\mathrm{MoSe_2}$ monolayers, encapsulated by hBN, in the full temperature range between $5-300 \mathrm{K}$. Using reflection spectroscopy measurements, we evaluate and compare the optical and polaritonic constituents of the TMD excitons in terms of oscillator strength, linewidth and negative permittivity. We find that it is $\mathrm{MoSe_2}$ that exhibits the most pronounced optical and polaritonic response, stemming from its rapid linewidth narrowing at low temperatures, as compared to the temperature-dependent response of the other TMDs. In addition, we find that all four TMDs exhibits a temperature-dependent negative real part permittivity, thus supporting surface-exciton-polaritons. We derive their dispersion relation, confinement factors and losses, similarly revealing that $\mathrm{MoSe_2}$ exhibit enhanced polaritonic properties. These findings establish a comparative framework for understanding the optical and polaritonic properties of monolayer TMDs, with implications on their utilization in optoelectronic devices based on 2D semiconductors.