Tracking the photoinduced dynamics of a dark excitonic state in single-layer WS$_2$ via resonant Autler-Townes splitting
Angela Montanaro, Francesco Valiera, Francesca Giusti, Francesca Fassioli, Chiara Trovatello, Giacomo Jarc, Enrico Maria Rigoni, Fang Liu, Xiaoyang Zhu, Stefano Dal Conte, Giulio Cerullo, Martin Eckstein, Daniele Fausti
Published: 2025/3/24
Abstract
Excitons in a monolayer transition metal dichalcogenide (1L-TMD) are highly bound states characterized by a Rydberg-like spectrum of discrete energy levels. Among these, states with odd-parity are known as dark excitons due to selection rules, which make their stationary and transient characterization challenging using linear optical techniques. Here, we demonstrate that the dynamics of a 2p dark excitonic state in 1L-WS$_2$ can be directly retrieved by measuring the Autler-Townes splitting of bright states in a three-pulse experiment. The splitting of the bright 1s excitonic state, observed by detuning a mid-infrared control field across the 1s-2p transition, provides an accurate characterization of the 2p state. Following carrier photoinjection, we observe a qualitatively different dynamics of the 1s and 2p levels, which is indicative of symmetry-dependent screening and exciton-exciton interactions. These findings provide new insights into many-body effects in TMDs, offering potential avenues for advancing the next generation optoelectronics.