Effects of Vanadium Doping on the Optical Response and Electronic Structure of WS_2 Monolayers
arxiv(2024)
摘要
Two-dimensional dilute magnetic semiconductors has been recently reported in
semiconducting transition metal dichalcogenides by the introduction of
spin-polarized transition metal atoms as dopants. This is the case of
vanadium-doped WS_2 and WSe_2 monolayers, which exhibits a ferromagnetic
ordering even above room temperature. However, a broadband characterization of
their electronic band structure and its dependence on vanadium concentration is
still lacking. Therefore, here we perform power-dependent photoluminescence,
resonant four-wave mixing, and differential reflectance spectroscopy to study
the optical transitions close to the A exciton energy of vanadium-doped WS_2
monolayers with distinct concentrations. Instead of a single A exciton peak,
vanadium-doped samples exhibit two photoluminescence peaks associated with
transitions to occupied and unoccupied bands. Moreover, resonant Raman
spectroscopy and resonant second-harmonic generation measurements revealed a
blueshift in the B exciton but no energy change in the C exciton as vanadium is
introduced in the monolayers. Density functional theory calculations showed
that the band structure is sensitive to the Hubbard U correction for
vanadium and several scenarios are proposed to explain the two
photoluminescence peaks around the A exciton energy region. Our work provides
the first broadband optical characterization of these two-dimensional dilute
magnetic semiconductors, shedding light on the novel electronic features of
WS_2 monolayers which are tunable by the vanadium concentration.
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