Revealing Excitonic Complexes in Monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>WS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> on Talc Dielectric
Gabriela Augusta Prando, Marion E. Severijnen, Ingrid D. Barcelos, U. Zeitler, Peter C. M. Christianen, Freddie Withers, Y. Galvão Gobato
Abstract
We report on a detailed study of low-temperature photoluminescence (PL) and magnetophotoluminescence under perpendicular magnetic fields (up to 30 T) and circularly polarized excitation on high-quality monolayer (ML) ${\mathrm{WS}}_{2}$ on a thick layer (120 nm) of talc dielectric. Remarkably, we obtained high-quality samples without any evidence of localized exciton emission at low temperature and a PL linewidth comparable to that of ${\mathrm{WS}}_{2}/h$-$\mathrm{BN}$ samples. As a consequence, we observe well-resolved emission peaks at low temperature due to the formation of excitonic complexes, including a dark-trion (DT) state and phonon replicas of the DT without the application of an in-plane magnetic field. The nature of the emission peaks, the magnetic field dependence of the degree of polarization, and g factors are discussed in detail and compared with the corresponding results obtained for $h$-$\mathrm{BN}$ encapsulated transition-metal dichalcogenide (TMD) samples. We observe that under ${\ensuremath{\sigma}}^{+}$-polarized excitation the sign of the circular polarization of biexcitons is reversed under higher magnetic fields. In addition, the dark-trion polarization increases considerably with increasing perpendicular magnetic field, demonstrating different behavior compared with previous studies of dark trions on monolayer ${\mathrm{WSe}}_{2}$. Our results suggest that talc is indeed a promising layered material for the surface protection of ML TMDs and to explore fundamental physics in view of applications in optoelectronic devices.