Momentum alignment and the optical valley Hall effect in low-dimensional Dirac materials

Abstract

We study the momentum alignment of photoexcited carriers and the optical control of valley population in gapless and gapped two-dimensional Dirac materials. The trigonal warping effect leads to the spatial separation of charge carriers belonging to different valleys upon linearly polarized high-frequency photoexcitation. Valley separation in gapped materials can be detected by measuring the degree of circular polarization of band-edge photoluminescence at different sides of the sample or light spot (optical valley Hall effect). We demonstrate that the celebrated Rashba effect, caused by substrate-induced system asymmetry, leads to a strong anisotropy in the low-energy part of the spectrum. This results in optical valley separation by a linearly polarized excitation at much lower frequencies compared to the high-energy trigonal warping regime. We also show that the momentum alignment phenomenon explains the giant enhancement of near-band-edge interband optical transitions in narrow-gap carbon nanotubes and graphene nanoribbons independent of the mechanism of the gap formation. These enhanced transitions can be used in terahertz emitters based on low-dimensional Dirac materials.

37 pages, 11 figures, published in the special issue of Journal of Experimental and Theoretical Physics dedicated to the 95th birthday of E.I. Rashba

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Cited by in corpus (6)

• Optical absorption in two-dimensional materials with tilted Dirac cones
• Bipolar electron waveguides in graphene
• Optical valley separation in two-dimensional semimetals with tilted Dirac cones
• Optically induced persistent current in carbon nanotubes
• Designer gapped and tilted Dirac cones in lateral graphene superlattices
• Electric and spin-valley currents induced by structured light in 2D Dirac materials