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Data for Indirect to direct gap crossover in two-dimensional InSe revealed by angle resolved photoemission spectroscopy Matthew Hamer (5244485) Johanna Zultak (2588755) Anastasia V. Tyurnina (6269831) Viktor Zólyomi (17513655) Daniel Terry (3183927) Alexei Barinov (1352226) Alistair Garner (5608043) Jack Donoghue (6269834) Aidan P. Rooney (3073800) Viktor Kandyba (4723164) Alessio Giampietri (6269837) Abigail J. Graham (11777303) Natalie C. Teutsch (11777300) Xue Xia (124699) Maciej Koperski (6269846) Sarah J. Haigh (1299489) Vladimir I. Fal'ko (17506665) Roman Gorbachev (4319653) Neil R. Wilson (1300776) Photoelectron spectroscopy -- Research Photoemission Oxide minerals -- Synthesis Migrated from ePrints Atomically thin films of III–VI post-transition metal chalcogenides (InSe and GaSe) form an interesting class of two-dimensional semiconductors that feature a strong variation of their band gap as a function of the number of layers in the crystal and, specifically for InSe, an expected crossover from a direct gap in the bulk to a weakly indirect band gap in monolayers and bilayers. Here, we apply angle-resolved photoemission spectroscopy with submicrometer spatial resolution (μARPES) to visualize the layer-dependent valence band structure of mechanically exfoliated crystals of InSe. We show that for one-layer and two-layer InSe the valence band maxima are away from the Γ-point, forming an indirect gap, with the conduction band edge known to be at the Γ-point. In contrast, for six or more layers the band gap becomes direct, in good agreement with theoretical predictions. The high-quality monolayer and bilayer samples enable us to resolve, in the photoluminescence spectra, the band-edge exciton (A) from the exciton (B) involving holes in a pair of deeper valence bands, degenerate at Γ, with a splitting that agrees with both μARPES data and the results of DFT modeling. Due to the difference in symmetry between these two valence bands, light emitted by the A-exciton should be predominantly polarized perpendicular to the plane of the two-dimensional crystal, which we have verified for few-layer InSe crystals.<br><br>Data description for ‘Indirect to direct gap crossover in two-dimensional InSe revealed by ARPES’ The photoluminescence and DFT data and headings in the files are self-explanatory (contact the corresponding authors if in doubt). Further details are given in the accompanying readme for the ARPES data files. 2019-01-24T00:00:00Z Dataset Dataset 10.82444/warw.33772765.v1 https://figshare.com/articles/dataset/Data_for_Indirect_to_direct_gap_crossover_in_two-dimensional_InSe_revealed_by_angle_resolved_photoemission_spectroscopy/33772765 CC BY 4.0