Electronic Structure and Spectroscopy of Two-Dimensional Materials

Two-dimensional materials, such as graphene and transition metal dichalcogenides, exhibit remarkable departures from bulk properties owing to reduced dimensionality and strong quantum confinement. Their electronic band structure evolves with layer number, stacking order and interlayer coupling, often undergoing an indirect-to-direct band gap transition in the monolayer limit. Strong spin–orbit coupling and broken inversion symmetry in certain semiconducting monolayers lead to valley-contrasting spin polarisation and coupled spin–valley degrees of freedom. Spectroscopic techniques, notably angle-resolved photoemission spectroscopy (ARPES) and its time-resolved variant, reveal the dispersion of electronic states, quasiparticle lifetimes and many-body renormalisations. Complementary methods, including scanning tunnelling microscopy and ultrafast optical spectroscopy, map local density of states, excitonic transitions and carrier dynamics. Theoretical approaches, spanning density functional theory to many-body perturbation theory, underpin the interpretation of experimental data and guide the design of heterostructures with tailored band alignments. This integrated knowledge of electronic structure and dynamics is central to the development of next-generation electronic, photonic and quantum technologies.

Research from Nature Portfolio

Recent studies have uncovered an interlayer plasmon polaron in graphene/WS2 heterostructures by employing micro-focused ARPES during in situ electron doping. A pronounced quasiparticle peak in the WS2 conduction band minimum was observed alongside multiple density-dependent shake-off replicas, signifying strong coupling between conduction electrons and an interlayer plasmon mode. This finding emphasises the impact of collective excitation coupling on the electronic landscape of van der Waals heterostructures.

Advances in spin- and angle-resolved ARPES of bulk MoS2 have revealed localised spin polarisation exceeding 65% in distinct valleys, despite global inversion symmetry. The observations attested to spin-layer locking and quasi-two-dimensional confinement of valence band states within individual trilayers, confirming that monolayer-like spin phenomena can be accessed without exfoliating to a single layer.

Electronic Structure and Spectroscopy of Two-Dimensional Materials publication trend

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

Technical terms

Angle-resolved photoemission spectroscopy (ARPES): direct probe of electronic band structure via measurement of kinetic energy and emission angle of photoelectrons.

Time- and angle-resolved photoemission spectroscopy (TR-ARPES): ultrafast variant of ARPES that captures carrier dynamics with femtosecond resolution.

Plasmon polaron: quasiparticle arising from strong coupling between charge carriers and collective plasmon modes.

Moiré pattern: periodic superlattice formed by rotational or lattice mismatch between stacked two-dimensional layers.

Type-II band alignment: band offset in heterostructures where conduction and valence band extrema reside in different layers, facilitating charge separation.

References

1. Observation of interlayer plasmon polaron in graphene/WS2 heterostructures. Nature Communications (2024).
2. Time- and angle-resolved photoemission spectroscopy (TR-ARPES) of TMDC monolayers and bilayers. Chemical Science (2023).
3. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals. Scientific Reports (2016).
4. Indirect to direct band gap crossover in two-dimensional WS2(1−x)Se2x alloys. npj 2D Materials and Applications (2021).
5. Strong interlayer hybridization in the aligned SnS2/WSe2 hetero-bilayer structure. npj 2D Materials and Applications (2019).