Valleytronics in Two-Dimensional Materials

Valleytronics exploits the valley degree of freedom, namely the occupation of discrete energy extrema (valleys) in momentum space, as a carrier of information in two-dimensional semiconductors and related heterostructures. Atomically thin transition-metal dichalcogenides, graphene derivatives and emerging Janus or magnetic monolayers each host inequivalent valleys at the corners of their Brillouin zone. Coupling between spin, layer or orbital pseudospins and valley index, often mediated by strong spin–orbit interaction or magnetic proximity, enables selective control of valley populations by optical, electric or magnetic means. Central concepts include valley polarisation, whereby an imbalance in valley occupation is achieved, and the valley Hall effect, in which Berry curvature deflects carriers of opposite valley flavour to opposite sample edges. Recent advances have demonstrated room-temperature valley polarisation, electric-field switchable anomalous valley transport and spontaneous valley ordering in otherwise inversion-symmetric lattices. The field now bridges fundamental studies of Berry‐phase physics with practical device paradigms for low-power logic, nonvolatile memory and quantum information. Integration of valley functionality with ferromagnetism, ferroelectricity or topological order further enriches the scope for multifunctional two-dimensional platforms.

Research from Nature Portfolio

Recent studies have demonstrated room-temperature valley polarisation in heterostructures of monolayer MoS₂ and chiral one-dimensional perovskites. When excited by linearly polarised light at near-resonance energies, these heterostructures exhibit measurable degrees of helicity-resolved photoluminescence polarisation, attributed to spin-selective charge transfer into the chiral perovskite acting as a spin filter. This approach provides a robust route to maintain valley polarisation against phonon-induced intervalley scattering at ambient temperature. A foundational framework introduced the concept of ferrovalley materials, exemplified by a 2H-VSe₂ monolayer in which intrinsic exchange coupling and strong spin–orbit interaction engender spontaneous valley polarisation. The same work predicted distinctive optical chirality dependence and an anomalous valley Hall effect, laying the groundwork for valley-based nonvolatile memories and filters. Further progress has been made in lifting valley degeneracy via magnetic proximity: monolayer WS₂ on a EuS substrate exhibits giant valley exciton splitting of order tens of meV per tesla, with a sign reversal in splitting for distinct surface terminations. First-principles analysis attributes this behaviour to competing ferromagnetic and antiferromagnetic exchange interactions, enabling tunable control of valley pseudospin for quantum-information applications.

Valleytronics in Two-Dimensional Materials publication trend

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

Technical terms

Valley: an energy extremum in the electronic band structure at discrete momentum-space points.

Valley polarisation: a population imbalance between inequivalent valleys of a crystal.

Berry curvature: a momentum-space property that acts like a magnetic field on electrons, giving rise to transverse anomalous velocities.

Valley Hall effect: the generation of a transverse valley current under an applied electric field, due to valley-dependent Berry curvature.

Ferrovalley material: a two-dimensional system possessing spontaneous valley polarisation in the absence of external fields.

References

1. Room temperature valley polarization via spin selective charge transfer. Nature Communications (2023).
2. Concepts of ferrovalley material and anomalous valley Hall effect. Nature Communications (2016).
3. Giant valley splitting in monolayer WS2 by magnetic proximity effect. Nature Communications (2019).
4. 2D spontaneous valley polarization from inversion symmetric single-layer lattices. npj Computational Materials (2022).
5. Anomalous valley Hall effect in antiferromagnetic monolayers. npj 2D Materials and Applications (2022).
6. Multifunctional two-dimensional van der Waals Janus magnet Cr-based dichalcogenide halides. npj Computational Materials (2022).