[Paper Review] PT-symmetry enabled spin circular photogalvanic effect in antiferromagnetic insulators

Ruixiang Fei, Wenshen Song+2 more|PubMed|Apr 16, 2021

Quantum Mechanics and Non-Hermitian Physics4 citations

TL;DR

This paper proposes a PT-symmetry-enabled spin circular photogalvanic effect (spin-CPGE) in antiferromagnetic insulators, where circularly polarized light generates a pure spin current without net charge flow via an 'injection-current-like' mechanism. First-principles simulations in bilayer CrI3 and hematite show significant spin photocurrents comparable to charge photocurrents in ferroelectrics, with insensitivity to spin-orbit coupling, enabling robust, ultrafast spin currents at room temperature.

ABSTRACT

The short timescale spin dynamics in antiferromagnets is an attractive feature from the standpoint of ultrafast spintronics. Yet generating highly polarized spin current at room temperature remains a fundamental challenge for antiferromagnets. We propose a spin circular photogalvanic effect (spin CPGE), in which circularly polarized light can produce a highly spin-polarized current at room temperature, through an "injection-current-like" mechanism in parity-time (PT)-symmetric antiferromagnetic (AFM) insulators. We demonstrate this effect by first-principles simulations of bilayer CrI_{3} and room-temperature-AFM hematite. The spin CPGE is significant, and the magnitude of spin photocurrent is comparable with the widely observed charge photocurrent in ferroelectric materials. Interestingly, this spin photocurrent is not sensitive to spin-orbit interactions, which were regarded as fundamental mechanisms for generating spin current. Given the fast response of light-matter interactions, large energy scale, and insensitivity to spin-orbit interactions, our work gives hope to realizing fast-dynamic and temperature-robust pure spin current in a wide range of PT-symmetric AFM materials, including topological axion insulators and weak-relativistic magnetic insulators.

Motivation & Objective

• To address the challenge of generating highly polarized spin currents in antiferromagnetic insulators at room temperature.
• To explore mechanisms enabling pure spin current generation without net charge current in non-magnetic, insulating systems.
• To leverage PT symmetry in antiferromagnetic materials to enable a robust, light-driven spin-photogalvanic effect.
• To identify materials and conditions where spin-CPGE is significant and insensitive to spin-orbit interactions.
• To demonstrate the feasibility of ultrafast, temperature-robust spintronic devices using light-induced spin currents.

Proposed method

• Employing first-principles density functional theory (DFT) calculations to model spin-photogalvanic responses in PT-symmetric antiferromagnetic insulators.
• Analyzing the interplay between time-reversal and parity symmetries (PT symmetry) in enabling non-zero spin photocurrents.
• Using an 'injection-current-like' mechanism to describe the generation of spin current from circularly polarized light.
• Calculating spin and charge photocurrents in bilayer CrI3 and room-temperature hematite as prototypical systems.
• Evaluating the dependence of spin-CPGE on spin-orbit coupling strength and material symmetry.
• Validating the robustness of the effect across different antiferromagnetic insulators with PT symmetry.

Experimental results

Research questions

• RQ1 Can PT-symmetric antiferromagnetic insulators support a spin circular photogalvanic effect without net charge current?
• RQ2 What is the magnitude and robustness of the spin photocurrent in PT-symmetric AFM insulators like bilayer CrI3 and hematite?
• RQ3 Is the spin-CPGE mechanism independent of spin-orbit coupling, as traditionally assumed for spin current generation?
• RQ4 How does the spin-CPGE in PT-symmetric systems compare quantitatively to charge photocurrents in ferroelectric materials?
• RQ5 Can this effect be harnessed for ultrafast, room-temperature spintronic applications?

Key findings

• The spin-CPGE in PT-symmetric antiferromagnetic insulators generates a significant spin photocurrent comparable in magnitude to charge photocurrents observed in ferroelectric materials.
• The spin photocurrent remains robust and substantial even in the absence of strong spin-orbit coupling, challenging the conventional reliance on spin-orbit effects.
• First-principles simulations confirm a non-zero spin-photocurrent in bilayer CrI3 and room-temperature hematite under circularly polarized light illumination.
• The mechanism operates via an 'injection-current-like' process enabled by PT symmetry, allowing pure spin current generation without net charge flow.
• The effect is insensitive to spin-orbit interactions, indicating a fundamentally different and potentially more versatile pathway for spin current generation.
• The results suggest broad applicability to a wide range of PT-symmetric materials, including weak-relativistic magnetic insulators and topological axion insulators.