Exciton Dynamics in Two-Dimensional Semiconductor Materials

Two-dimensional semiconductors, notably monolayer transition metal dichalcogenides and their heterostructures, host tightly bound electron–hole pairs known as excitons. Owing to reduced dielectric screening and enhanced Coulomb interactions, these quasiparticles display binding energies of hundreds of millielectronvolts and remain stable at room temperature. Exciton formation, energy relaxation and recombination proceed via a complex interplay of phonon scattering, many-body interactions and coupling to the electromagnetic field. Bright excitons radiatively recombine within picosecond to nanosecond timescales, while momentum-indirect or “dark” states introduce non-radiative channels that influence coherence lifetimes and emission linewidths. In engineered lateral and vertical heterostructures, interlayer and charge-transfer excitons exhibit long lifetimes and large dipole moments, offering routes for efficient exciton transport and dissociation. Moiré superlattices further enrich this landscape by confining excitons into periodic potentials, enabling tunable interactions and emergent correlated phases. Understanding these dynamics is crucial for advancing light-emitting devices, ultrafast photodetectors, exciton-based logic and quantum information technologies worldwide.

Research from Nature Portfolio

Recent studies have elucidated the microscopic mechanisms governing exciton behaviour in lateral and monolayer heterostructures. In hBN-encapsulated MoSe₂–WSe₂ junctions, bound charge-transfer excitons emerge for interfaces narrower than the Coulomb Bohr radius; theory and low-temperature photoluminescence reveal tunable binding energies of a few tens of millielectronvolts and strong dipole moments that facilitate rapid propagation and efficient dissociation. A fully quantum-mechanical treatment of monolayer MoSe₂ has mapped the momentum- and energy-resolved formation, radiative recombination and phonon-induced cascade relaxation of excitons, highlighting spectroscopic signatures of each stage in pump-probe experiments. Investigations into monolayer WS₂ and MoSe₂ have identified phonon-mediated intravalley and intervalley scattering into momentum-dark states, quantifying their impact on coherence lifetimes and homogeneous linewidths and establishing temperature-dependent dephasing pathways fundamental to coherent control schemes.

Research from all publishers

Hybrid photonic platforms combining WS₂ monolayers with dielectric nanoantennas have demonstrated suppression of exciton–exciton annihilation under high excitation densities, achieving over two orders of magnitude enhancement in photoluminescence and reduced annihilation coefficients through intermediate light–matter coupling. Femtosecond pump-push-probe spectroscopy of WS₂ monolayers has revealed an intrinsic carrier cooling rate of approximately 18 eV/ps, modulated by hot-phonon bottlenecks and carrier-carrier scattering, with subpicosecond trapping by lattice defects. In MoSe₂/WS₂ moiré heterostructures, nonlinear pump–probe measurements exploiting the ac Stark effect have probed interactions among confined excitons and polarons, uncovering density-dependent blueshifts and a breakdown of the Fermi-polaron description under strong moiré confinement.

Exciton Dynamics in Two-Dimensional Semiconductor Materials publication trend

The graph below shows the total number of articles in exciton dynamics in two-dimensional semiconductor materials across all publications each year (not limited to Nature Index journals).

Technical terms

Exciton: A bound state of an electron and a hole held together by Coulomb attraction in a semiconductor.

Dark exciton: An exciton with momentum or spin configuration that prevents direct radiative recombination, leading to non-radiative decay channels.

Charge-transfer exciton: An exciton in which the electron and hole reside in adjacent layers or distinct materials, resulting in large dipole moments.

Phonon: A quantised vibrational mode of the crystal lattice that mediates energy and momentum exchange with excitons.

Moiré potential: A spatially periodic potential arising from the lattice mismatch or twist angle between stacked two-dimensional layers, confining excitons in superlattice sites.

Exciton–exciton annihilation (EEA): A non-radiative process in which two excitons interact and one recombines, transferring energy to the other and reducing emission efficiency.

Coherence lifetime: The duration over which an exciton maintains a well-defined phase relationship, determining the homogeneous contribution to emission linewidth.

References

1. Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors. npj 2D Materials and Applications (2018).
2. Interface engineering of charge-transfer excitons in 2D lateral heterostructures. Nature Communications (2023).
3. Exciton Relaxation Cascade in two-dimensional Transition Metal Dichalcogenides. Scientific Reports (2018).
4. Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides. Nature Communications (2016).
5. Intrinsic homogeneous linewidth and broadening mechanisms of excitons in monolayer transition metal dichalcogenides. Nature Communications (2015).
6. Radiative suppression of exciton–exciton annihilation in a two-dimensional semiconductor. Light: Science & Applications (2023).
7. Hot Carrier Cooling and Trapping in Atomically Thin WS2 Probed by Three-Pulse Femtosecond Spectroscopy. ACS Nano (2023).
8. ac Stark Spectroscopy of Interactions between Moiré Excitons and Polarons. Physical Review X (2025).