Electronic bandstructure of ReS2 by high resolution angle resolved photoemission spectroscopy

Abstract

The rhenium-based transition metal dichalcogenides (TMDs) are atypical of the TMD family due to their highly anisotropic crystalline structure and are recognized as promising materials for two dimensional heterostructure devices. The nature of the band gap (direct or indirect) for bulk, few and single layer forms of ReS${}_2$ is of particular interest, due to its comparatively weak inter-planar interaction. However, the degree of inter-layer interaction and the question of whether a transition from indirect to direct gap is observed on reducing thickness (as in other TMDs) are controversial. We present a direct determination of the valence band structure of bulk ReS${}_2$ using high resolution angle resolved photoemission spectroscopy (ARPES). We find a clear in-plane anisotropy due to the presence of chains of Re atoms, with a strongly directional effective mass which is larger in the direction orthogonal to the Re chains (2.2 $m_e$) than along them (1.6 $m_e$), in good agreement with density functional theory calculations. An appreciable inter-plane interaction results in an experimentally-measured difference of ~100-200 meV between the valence band maxima at the Z point (0,0,1/2) and the $\Gamma$ point (0,0,0) of the three-dimensional Brillouin zone. This leads to a direct gap at Z and a close-lying but larger gap at $\Gamma$, implying that bulk ReS2 is marginally indirect. This may account for recent conflicting transport and photoluminescence measurements and the resulting uncertainty about the direct or indirect gap nature of this material.

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• Additional excitonic features and momentum-dark states in ReS2
• Non equilibrium anisotropic excitons in atomically thin ReS${}_2$
• Electronic band structure of rhenium dichalcogenides
• Giant Transport Anisotropy in ReS${}_2$ Revealed via Nanoscale Conducting Path Control
• Two-dimensional ReS2: Solution to the Unresolved Queries on Its Structure and Inter-layer Coupling Leading to Potential Optical Applications
• Prevalence of oxygen defects in an in-plane anisotropic transition metal dichalcogenide
• Vibrational and dielectric properties of monolayer transition metal dichalcogenides
• Interplay of crystal thickness and in-plane anisotropy and evolution of quasi-one dimensional electronic character in ReSe${}_2$
• Using in-plane anisotropy to engineer Janus monolayers of rhenium dichalcogenides
• Electronic band structure in pristine and Sulfur-doped Ta${}_2$NiSe${}_5$
• Local electric field induced spin photocurrent in ReS2