Breakdown of Spin-to-Helicity Locking at the Nanoscale in Topological Photonic Crystal Edge States

Journal article (2022)

Authors

S. Arora Kavli institute of nanoscience Delft, QN/Kuipers Lab - AS
T.A. Bauer QN/Kuipers Lab - AS , Kavli institute of nanoscience Delft
L. Kuipers QN/Quantum Nanoscience
Research Group
QN/Kuipers Lab (AS) (TU Delft)
Copyright: © 2022 S. Arora, T.A. Bauer, N. Parappurath, R.T. Barczyk, E. Verhagen, L. Kuipers
DOI: https://doi.org/10.1103/PhysRevLett.128.203903
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Published Date

2022

Language

English

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Faculty

Applied Sciences

Department

QN/Quantum Nanoscience

Research Group

QN/Kuipers Lab

Abstract

We measure the local near-field spin in topological edge state waveguides that emulate the quantum spin Hall effect. We reveal a highly structured spin density distribution that is not linked to a unique pseudospin value. From experimental near-field real-space maps and numerical calculations, we confirm that this local structure is essential in understanding the properties of optical edge states and light-matter interactions. The global spin is reduced by a factor of 30 in the near field and, for certain frequencies, flipped compared to the pseudospin measured in the far field. We experimentally reveal the influence of higher-order Bloch harmonics in spin inhomogeneity, leading to a breakdown in the coupling between local helicity and global spin.

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