Population pulsation resonances of excitons in monolayer MoSe2 with sub 1 {\mu}eV linewidth

TL;DR

This study reveals ultra-narrow population pulsation resonances in monolayer MoSe2, indicating exceptionally long-lived exciton states and providing new insights into exciton relaxation dynamics in 2D semiconductors.

Contribution

The paper demonstrates the observation of population pulsation resonances with linewidths below 1 { extmu}eV in monolayer MoSe2, revealing long-lived exciton states not previously characterized.

Findings

Linewidths of 1 { extmu}eV and <0.2 { extmu}eV observed

Long-lived exciton states exceeding 6 ns identified

Resonances are over three orders narrower than photoluminescence linewidths

Abstract

Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe2 using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 {\mu}eV and <0.2 {\mu}eV at low-temperature. These linewidths are more than three orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on timescales longer than 1 ns. The ultra-narrow resonance (<0.2 {\mu}eV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.