Intrinsic efficiency of injection photocurrents in magnetic materials

TL;DR

This paper investigates the efficiency of injection photocurrents in magnetic materials, revealing that only ballistic magnetic injection currents can have finite efficiency at large relaxation times, and provides a band structure expression for their efficiency.

Contribution

It introduces a band structure expression for the efficiency of magnetic injection photocurrents and highlights their potential for energy harvesting in magnetic materials.

Findings

Ballistic photocurrents have finite efficiency only at large relaxation times.

Magnetic injection current is the only finite ballistic current at zero temperature for unpolarized light.

Efficiency scales as $( ext{hbar} \Omega - E_g)^2$ near the band edge.

Abstract

The generation of shift and ballistic photocurrents in non-centrosymmetric materials represents a promising alternative mechanism for light energy harvesting. Many studies have focused on finding the best suited materials by maximizing the photocurrent magnitude, but estimating the actual efficiency requires knowledge of the light-induced DC photoconductivity and is rarely considered. Using the recently proposed jerk current as photoconductivity, in this work we show that only ballistic photocurrents have finite efficiency in the limit of large relaxation times $\tau$. Moreover, at zero temperature the only ballistic current which is finite for unpolarized light is the magnetic injection current, only present in magnetic materials. We present a band structure expression for the efficiency of such photocurrent, showing that it scales as $(\hbar \Omega-E_g)^2$ near the band edge, and we present its frequency dependence for a simple tight-binding model. Our work provides a new tool to guide the search for efficient energy harvesting based on the magnetic injection current.