Giant Magneto-refractive Effect in Second Harmonic Generation from Plasmonic Antennas in the Mid-infrared

TL;DR

This paper demonstrates a 20% magnetic field-induced modulation of second harmonic generation in plasmonic antennas, revealing a novel spin-dependent nonlinear susceptibility mechanism in mid-infrared nanostructures.

Contribution

It introduces a new magneto-refractive effect in nonlinear optics using spintronic multilayer antennas, with a mechanism based on spin-dependent electron mean free path.

Findings

Achieved 20% modulation of SHG with magnetic field

Identified spin-dependent electron mean free path as key mechanism

No resonance shift observed during modulation

Abstract

Metallic nanostructures exhibit strong nonlinear-optical response at surface plasmon resonances, where the light-matter coupling efficiency is enhanced. An active modulation of this response can be realized by means of an external magnetic field. Here we utilize a nonlinear magneto-refractive effect in spintronic multilayer antennas to achieve a resonant 20\% modulation in second harmonic generation (SHG) in the mid-infrared. We discuss mechanisms of this modulation and show that it cannot be explained by an unequal enhancement of the electromagnetic field in the two spin states of the multilayer. Instead, we propose a novel contribution to the nonlinear susceptibility, which relies on the spin-dependent electron mean free path in metals. In contrast to magneto-optics in ferromagnets, our approach results in no shift of the resonance and thus ensures that the largest SHG and its strongest modulation are simultaneously observed.