Coherence and density dynamics of excitons in a single-layer MoS${}_2$ reaching the homogeneous limit

Abstract

We measure the coherent nonlinear response of excitons in a single-layer of molybdenum disulphide embedded in hexagonal boron nitride, forming a $h$-BN/MoS${}_2$/$h$-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton homogeneous and inhomogeneous broadenings. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultra-fast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the $h$-BN and imperfections in the encapsulation process.

References in corpus (25)

• Atomically thin MoS2: A new direct-gap semiconductor
• Control of valley polarization in monolayer MoS2 by optical helicity
• Valley polarization in MoS2 monolayers by optical pumping
• MoS_2 as an ideal material for valleytronics: valley-selective circular dichroism and valley Hall effect
• The Valley Hall Effect in MoS2 Transistors
• Phonons in single and few-layer MoS2 and WS2
• Strong light-matter coupling in two-dimensional atomic crystals
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Low-temperature photocarrier dynamics in monolayer MoS2
• Excitonic linewidth approaching the homogeneous limit in MoS2 based van der Waals heterostructures : accessing spin-valley dynamics
• Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides
• Exciton Radiative Lifetime in Transition Metal Dichalcogenide Monolayers
• Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS${}_2$ and MoS${}_2$ to 65 Tesla
• Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
• Nonanalyticity, Valley Quantum Phases, and Light-like Exciton Dispersion in Monolayer TMDs: Theory and First-Principles Calculations
• Exciton Dynamics in Monolayer Transition Metal Dichalcogenides
• Evidence of giant oscillator strength in the exciton dephasing of CdSe nanoplatelets measured by resonant four-wave mixing
• Exciton and trion dynamics in atomically thin MoSe2 and WSe2: effect of localization
• Enabling valley selective exciton scattering in monolayer WSe${}_2$ through upconversion
• Observing imperfection in atomic interfaces for van der Waals heterostructures
• Magneto-excitons in large area CVD grown monolayer MoS${}_2$ and MoSe${}_2$ on sapphire
• Opto-valleytronic imaging of atomically thin semiconductors
• Weakly Trapped, Charged, and Free Excitons in Single-Layer MoS2 in the Presence of Defects, Strain, and Charged Impurities
• Resonantly excited exciton dynamics in two-dimensional MoSe${}_2$ monolayers
• Identifying optical signatures of momentum-dark excitons in transition metal dichalcogenide monolayers