Excitonic effects in the photocarriers dynamics of two-dimensional materials

Abstract

We investigate the role of excitonic correlations in shaping the ultrafast dynamics of photoexcited carriers in semiconductors. Conventional approaches describe relaxation within single-particle frameworks, where electron-electron and electron-phonon scattering drive thermalization toward Fermi-Dirac distributions, neglecting electron-hole correlations that dominate near band edges. We introduce a two-particle framework based on excitonic Bloch equations (XBE) that captures carrier-phonon scattering and explicitly accounts for exciton formation. Applying this approach to non-resonantly photoexcited WSe${}_2$ monolayers, we reveal qualitatively different carrier relaxation pathways: in contrast to state-of-the-art methods, XBE predict enhanced intervalley scattering and dominant carrier population in Q valleys over K valleys, in agreement with time-resolved ARPES experiments. Moreover, the momentum distribution of thermalized carriers is shaped by exciton wavefunctions rather than by Fermi-Dirac statistics, signaling the formation of a correlated nonequilibrium state. These results establish excitonic correlations as a key mechanism governing photocarrier dynamics in excitonic materials.

14 pages, 5 figures

References in corpus (15)

• Intervalley scattering in MoS${}_2$ imaged by two-photon photoemission with a high-harmonic probe
• Ultrafast dynamics of electrons and phonons: from the two-temperature model to the time-dependent Boltzmann equation
• Witnessing the formation and relaxation of massive quasi-particles in a strongly correlated electron system
• Nonequilibrium Lattice Dynamics in Monolayer MoS2
• Real-time GW: Toward an ab initio description of the ultrafast carrier and exciton dynamics in two-dimensional materials
• Time-linear scaling NEGF methods for real-time simulations of interacting electrons and bosons. I. Formalism
• Strong Coupling of Coherent Phonons to Excitons in Semiconducting Monolayer MoTe${}_2$
• Time-linear scaling NEGF methods for real-time simulations of interacting electrons and bosons. II. Dynamics of polarons and doublons
• Ultrafast photoluminescence in metals: Theory and its application to silver
• Exciton-phonon interaction calls for a revision of the "exciton" concept
• Complete collisions approximation to the Kadanoff-Baym equation: a first--principles implementation
• Excitonic Bloch equations from first principles
• Advancing Simulations of Coupled Electron and Phonon Nonequilibrium Dynamics Using Adaptive and Multirate Time Integration
• Measuring the ultrafast screening of $U$ in photo-excited charge-transfer insulators with time-resolved X-ray absorption spectroscopy
• Nonequilibrium Photocarrier and Phonon Dynamics from First Principles: a Unified Treatment of Carrier-Carrier, Carrier-Phonon, and Phonon-Phonon Scattering