Observation of second-harmonic generation induced by pure spin currents

TL;DR

This paper demonstrates a novel second-order nonlinear optical effect induced by pure spin currents, enabling real-time, non-invasive imaging of spin currents across various materials, advancing spintronics research and applications.

Contribution

It introduces the first observation of a nonlinear optical effect caused by pure spin currents, providing a new method for their detection and imaging.

Findings

First demonstration of second-harmonic generation by pure spin currents

Enables real-time, non-destructive imaging of spin currents

Applicable to a wide range of materials without optical resonance dependence

Abstract

Extensive efforts are currently being devoted to developing a new electronic technology, called spintronics, where the spin of electrons is explored to carry information. [1,2] Several techniques have been developed to generate pure spin currents in many materials and structures. [3-10] However, there is still no method available that can be used to directly detect pure spin currents, which carry no net charge current and no net magnetization. Currently, studies of pure spin currents rely on measuring the induced spin accumulation with optical techniques [5, 11-13] or spin-valve configurations. [14-17] However, the spin accumulation does not directly reflect the spatial distribution or temporal dynamics of the pure spin current, and therefore cannot monitor the pure spin current in a real-time and real-space fashion. This imposes severe constraints on research in this field. Here we demonstrate a second-order nonlinear optical effect of the pure spin current. We show that such a nonlinear optical effect, which has never been explored before, can be used for the non-invasive, non-destructive, and real-time imaging of pure spin currents. Since this detection scheme does not rely on optical resonances, it can be generally applied in a wide range of materials with different electronic bandstructures. Furthermore, the control of nonlinear optical properties of materials with pure spin currents may have potential applications in photonics integrated with spintronics.