Excitonic Properties in Two-Dimensional Semiconductor Materials

Atomically thin semiconductors such as transition-metal dichalcogenides exhibit exceptionally strong Coulomb interactions and reduced dielectric screening, leading to tightly bound electron–hole pairs known as excitons. These excitons display binding energies of hundreds of millielectronvolts, radii of the order of a nanometre and a rich Rydberg series of excited states. Reduced dimensionality also gives rise to spin-valley coupling, optical selection rules and dark exciton manifolds, while environmental factors such as substrate choice, encapsulation and interlayer twist angle allow precise tuning of bandgaps and exciton dynamics. More complex quasiparticles including charged excitons (trions), biexcitons and Fermi polarons emerge under electrostatic doping or at high excitation densities. Studies of excitonic linewidths, valley Zeeman effects and diamagnetic shifts provide fundamental parameters—effective masses, radii, binding energies—essential for the rational design of optoelectronic and quantum devices based on van der Waals heterostructures. Advances in photoluminescence upconversion, cavity coupling and heterostructure engineering are paving the way for next-generation lasers, optical cooling platforms and valleytronic applications.

Research from Nature Portfolio

Recent studies have demonstrated dramatic enhancement of anti-Stokes photoluminescence in monolayer WSe₂ by harnessing plasmonic nano-cavities to resonantly excite dark exciton transitions at room temperature. A near-hundred-fold increase in upconverted emission intensity is achieved by optimising nanoparticle geometry, with reversible electrochemical gating enabling on-demand switching. High-field magneto-optical spectroscopy of several monolayer dichalcogenides has mapped the diamagnetic shifts and valley Zeeman splittings of ground and excited exciton states up to Rydberg levels, yielding direct measurements of reduced masses, binding energies and free-particle bandgaps—parameters critical for heterostructure design. Encapsulation of WSe₂ in hexagonal boron nitride has allowed unambiguous identification and electrical control of neutral and charged biexciton complexes, resolving their binding energies and fine-structure splittings and offering routes to electrically switch multi-exciton states for quantum light sources.

Research from all publishers

Phonon-assisted photon upconversion in twisted bilayers of WSe₂ reveals a four-fold enhancement in anti-Stokes emission at specific twist angles, linked to lattice relaxation and spectral redshift effects. This work highlights the role of moiré engineering in tuning interlayer exciton conversion and light–matter interaction for stacked van der Waals devices. Investigations of doped MoSe₂ monolayers have observed both attractive and repulsive Fermi polarons, confirming theoretical predictions of energy splitting and quantum dephasing behaviour as a function of carrier density; insights from these measurements inform understanding of pairing mechanisms and magnetic instabilities in two dimensions. Encapsulation of MoS₂ in hexagonal boron nitride has suppressed inhomogeneous broadening to yield excitonic linewidths approaching the homogeneous limit at cryogenic temperatures, enabling precise studies of phonon-induced broadening and valley coherence dynamics and emphasising the importance of surface protection for high-quality samples.

Excitonic Properties in Two-Dimensional Semiconductor Materials publication trend

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

Technical terms

Exciton: A bound electron–hole pair held together by Coulomb attraction in a semiconductor.

Trion: A charged exciton formed by an exciton binding with an additional free electron or hole.

Biexciton: A four-particle complex comprising two electrons and two holes bound by Coulomb interactions.

Fermi polaron: A quasiparticle arising when an impurity interacts with a Fermi sea of charge carriers.

Dielectric screening: Reduction of Coulomb interaction strength due to the surrounding medium’s polarisation.

Dark exciton: An exciton with an optically forbidden transition dipole, requiring alternative channels for excitation or emission.

References

1. Phonon-assisted upconversion in twisted two-dimensional semiconductors. Light: Science & Applications (2023).
2. Photoluminescence upconversion in monolayer WSe2 activated by plasmonic cavities through resonant excitation of dark excitons. Nature Communications (2023).
3. Quantum Dynamics of Attractive and Repulsive Polarons in a Doped MoSe2 Monolayer. Physical Review X (2023).
4. Excitonic Linewidth Approaching the Homogeneous Limit in MoS2-Based van der Waals Heterostructures. Physical Review X (2017).
5. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nature Communications (2017).
6. Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields. Nature Communications (2019).
7. Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2. Nature Communications (2018).
8. Charge-tuneable biexciton complexes in monolayer WSe2. Nature Communications (2018).