Experimental Probing of Canonical Electromagnetic Spin Angular Momentum Distribution via Valley-Polarized Photoluminescence

Donghyeong Kim and Min-Kyo Seo

Phys. Rev. Lett. 127, 223601 – Published 24 November 2021

Abstract

The canonical formulation of the spin angular momentum (SAM) of light has been suggested recently as an extension of the Abraham-Minkowski controversy. However, experimental substantiations of the canonical SAM for localized fields have not been reported yet. We directly probe the locally distributed canonical SAM tailored by a plasmonic nanostructure via the valley-polarized photoluminescence of the multilayer ${WS}_{2}$ . The spectrum-resolved measurement details the spin-selective Raman scattering and exciton emission beyond the conventional manner of employing circularly polarized paraxial waves.

Received 28 July 2021
Accepted 28 October 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.223601

Physics Subject Headings (PhySH)

Angular momentum of light Nanophotonics Near-field optics Plasmonics

Atomic, Molecular & Optical

Authors & Affiliations

Donghyeong Kim and Min-Kyo Seo ^*

Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea

^*Corresponding author. minkyo_seo@kaist.ac.kr

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Issue

Vol. 127, Iss. 22 — 24 November 2021

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Images

Figure 1
(a) Schematic of the local distribution of the canonical SAM generated by an optical nanostructure and probed by the valley-polarized PL of the multilayer ${WS}_{2}$ . (b) Typical valley-polarized PL spectrum of the employed multilayer ${WS}_{2}$ flake under the planewave 594-nm-laser excitation of the left-handed circular polarization. In the spectrum, the DoCP of the $A$ exciton emission is $\sim 0.8 3$ . (c,d) Measured distributions of the left- and right-handed circularly polarized PL (c) and the DoCP (d) over the multilayer ${WS}_{2}$ flake under the left-handed circularly polarized excitation. Scale bar, $10 μ m$ .
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Figure 2
(a) Calculated distribution of the vertical component ( $S_{z}$ ) of the canonical SAM density generated by the connected V-shape gold structure under the planewave incidence, linearly polarized along the $y$ axis; scale bar, 200 nm. (b) Calculated canonical SAM distribution over the nanostructure array (left) and expected valley-polarized PL distribution considering the diffraction by the objective lens (right). (c) Scanning electron microscope image of the fabricated connected V-shape gold nanostructure array; scale bar, $1 μ m$ . (d) Optical microscope image of the measured sample. The V-shape gold nanostructure array (the white box) entirely overlays the multilayer ${WS}_{2}$ flake (the area below the white dashed line); scale bar, $2.5 μ m$ . (e),(f) Measured PL intensity distributions with the left- (e) and right-handed (f) circular polarization states. The step size of scanning is 166.7 nm. The green dashed lines guide the positions of the nodes of PL for comparison; scale bar, $1 μ m$ . (g) Measured canonical SAM distribution; scale bar, $1 μ m$ . (h) Measured (black) and calculated (red) $C_{+} - C_{-}$ depending on the position along the $y$ axis.
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Figure 3
(a),(b) Measured PL spectra of the left- (a) and right-handed (b) circular polarization depending on the position along the white dashed lines in Figs. 2 and 2, respectively. (c) PL spectra at two different $y$ positions indicated by the white dashed lines in (a). (d) The stack plot of the PL intensities of the $A$ exciton and Raman scattering of the $A_{1 g}$ and $E_{2 g}^{1}$ modes depending on the position along the $y$ axis as the canonical SAM essentially changes. Stack offset is 30 counts.
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Figure 4
(a) Schematic of the response of the dye molecule layer (Texas red dye molecule) that washes out the canonical SAM distribution. (b),(c) Measured PL intensity distributions with the left- (b) and right-handed (c) circular polarization states; scale bar, $1 μ m$ . The green box indicates the area of the connected V-shape gold nanostructure array. (d). Difference between the PL intensity measured in (b) and (c).
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