Mid-Infrared Optical Spin Injection and Coherent Control

TL;DR

This study explores how adding Sn to Ge semiconductors enables mid-infrared optical spin injection and coherent control, with enhanced spin polarization and response tensors, useful for quantum sensing applications.

Contribution

It provides a detailed analysis of spin injection and coherent control in Ge$_{1-x}$Sn$_{x}$, revealing how Sn incorporation enhances spin polarization and response tensors, advancing quantum manipulation techniques.

Findings

Sn increases one-photon spin polarization at E1 resonance.

Response tensors exponentially grow with Sn content near the band edge.

Two-photon DSP exceeds 60% at Sn content above 14%.

Abstract

The optical injection of charge and spin currents are investigated in Ge$_{1-x}$Sn$_{x}$ semiconductors as a function of Sn content. These emerging silicon-compatible materials enable the modulation of these processes across the entire mid-infrared range. Under the independent particle approximation, the one- and two-photon interband absorption processes are elucidated, and the evolution of the coherent control is discussed for three different polarization configurations. To evaluate the contribution of high-energy transitions, a full-zone 30-band k$\cdot$p is employed in the calculations. It was found that, besides the anticipated narrowing of the direct gap and the associated shift of the absorption to longer wavelengths, incorporating Sn in Ge also increases the one-photon degree of spin polarization (DSP) at the $E_1$ resonance. Moreover, as the Sn content increases, the magnitude of the response tensors near the band edge exhibits an exponential enhancement. This behavior can be attributed to the Sn incorporation-induced decrease in the carrier effective masses. This trend appears to hold also at the $E_1$ resonance for pure spin current injection, at least at low Sn compositions. The two-photon DSP at the band edge exceeds the value in Ge to reach 60 % at a Sn content above 14 %. These results demonstrate that Ge$_{1-x}$Sn$_{x}$ semiconductors can be exploited to achieve the quantum coherent manipulation in the molecular fingerprint region relevant to quantum sensing.