Direct observation of photonic spin Hall shift in Mie scattering

The photonic spin Hall shift is an optical equivalent of the celebrated electron transport phenomenon in solid-state physics. Although the latter results in the lateral separation of electrons with opposite spins within a current flow, the former refers to a splitting of circularly polarized photons of opposite handedness upon reflection or refraction at material interfaces. Intriguingly, due to the conservation of total angular momentum intrinsically, the photonic spin Hall shift must persist upon transition from an interface to a stand-alone particle, where it would manifest itself via Mie scattering as a seeming shift of the particle’s location. Such a peculiar phenomenon is extremely challenging to observe and has remained elusive because its magnitude is inversely related to measurable light intensity, and the fundamental trade-off is particularly severe for scattering off sub-wavelength particles. We overcame this longstanding challenge by combining the regime of enhanced superscattering due to inter-multipolar energy exchange with strong near-field spin-orbit interaction, which enabled boosting the scattering efficiency by nearly two orders of magnitude and allowed its post selection-free detection at experimentally convenient angles in the microwave regime.ToC. The photonic spin Hall shift is difficult to observe because its magnitude is inversely related to measurable intensity. We overcome this limitation by combining strong near-field spin-orbit coupling with superscattering due to inter-multipolar energy exchange. This approach boosts scattering intensity at the maximum shift by nearly two orders of magnitude, enabling direct observation without weak or indirect measurements.