22 June 2022 Wed 4 pm

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Atomically thin transition metal dichalcogenides (TMDs) have attracted great interest as a novel two-dimensional platform exhibiting exotic optoelectronic properties. However, a photocurrent generation without an external field is not allowed by the C3v rotational symmetry of TMDs. Recently, the spontaneous photocurrent has been realized by breaking the symmetry in one-dimensional WS2 nanotubes [Zhang et al., Nature 570, 349 (2019)]. In this talk, we reveal the underlying mechanism of the shift current generation in reduced dimension and suggest a new type of giant photovoltaic effect in response to visible light in WS2 double-walled nanotubes. We find that a significant shift current is induced by d-d transition with the aid of the axial polarization in single-walled nanotubes and it is extremely enhanced by the wall-to-wall charge shift in doubled-walled nanotubes. Furthermore, we propose that the symmetry breaking perpendicular to the tubular direction by substitution of one chalcogen layer (Janus type of TMDs nanotube) can produce 2.5 times larger shift current than the pristine WS2 nanotube. To assess the nonlinear effect of a strong field and the nonadiabatic effect of atomic motion, we carry out direct real-time integration of the photoinduced current using time-dependent density functional theory. Our findings provide a solid basis for a complete quantum mechanical understanding of the unique light–matter interaction hidden in the geometric characteristics of the reduced dimension.

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