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Abstract
The emergence of valley selectivity in tin(ii) sulphide is explained with the use of density functional theory and the momentum operator matrix elements for the optical transitions. After application of electric stress, the polarization efficiency was found to decrease in the zigzag direction. Wannier functions are further used to derive an effective Tight Binding (TB) model. The velocity matrix elements of the Wannier functions reveal further details about how the p orbitals of Sn and S contribute to optical transitions. Using the TB model in the Wannier basis in a nanoribbon configuration, the bandgap shows an overall decrease as the width of the nanoribbon increases for both zigzag and armchair directions of the structure up to ≈42 Å further presenting opportunities for Optoelectronic applications.
Highlights
Valleytronics is an attractive alternative to future electronics due to the low power dissipation that they promise.[1]
Graphene and Transition Metal Dichalcogenides (TMD) MX2 (M 1⁄4 Mo, W, X 1⁄4 Se, S) have been extensively studied for the emergence of the relevant physical phenomena tied to the underlying crystal symmetries, including optical selection rules that allow pseudospin up, down and their superposition to be realized
We use rst principles methods and Wannier functions (WFs), to show how optical selection rules arise from the crystal symmetries, orbital analysis and the matrix elements of the momentum operator
Summary
Valleytronics is an attractive alternative to future electronics due to the low power dissipation that they promise.[1]. Due to the valleys that exist in the x and y directions of their BZ, linearly polarized light in each real space direction induces optical excitations in the equivalent reciprocal space direction.[8,9,10,11] It has been predicted that, if an electric eld is applied in one of these directions, a current with transverse component will be created that results from the absence of mirror symmetry of the valleys that exist in two sets of time-reversed images of one another at the axes of the BZ.[9] Selection of each valley in this case results from the chosen direction for the application of the electric eld and the current appears on the edges of the sample, equivalent to the valley hall effects in TMDs. We use rst principles methods and Wannier functions (WFs), to show how optical selection rules arise from the crystal symmetries, orbital analysis and the matrix elements of the momentum operator. Valley-selective linear dichroism has been reported for bulk[10] and SnS akes down to 50 nm.[11]
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