Optical sensing of charge and spin current fluctuations in centrosymmetric semiconductors

TL;DR

This paper proposes a non-invasive, all-optical method to detect transient charge and spin currents in centrosymmetric semiconductors using second harmonic generation and homodyne amplification, enabling fluctuation analysis without electrical contact.

Contribution

It introduces a novel optical measurement scheme leveraging third-order nonlinear processes to sample current fluctuations in bulk semiconductors without electrical contacts.

Findings

Detects charge current in GaAs at room temperature

Uses homodyne amplification to enhance weak signals

Enables non-invasive fluctuation measurements

Abstract

We propose a time-resolved optical measurement scheme for sampling transient charge and spin currents in a bulk centrosymmetric semiconductor. The technique relies on emission of second harmonic light triggered by a pulsed below-gap optical excitation and a spontaneous intraband polarization arising from spin or charge motion, mediated by a $\chi^(3)$-based nonlinear optical process. Our proposal uses homodyne amplification to boost the weak second harmonic signal, making it detectable with conventional electronics, calculated for charge current in a room temperature GaAs semiconductor. This all-optical technique requires neither electrical contact nor bias fields and the signal is estimated at a few percent relative to the shot noise of the probe. This proposal motivates a novel method for exploring thermal and quantum fluctuations in the solid state in a non-invasive manner.