Antiferromagnetism-induced second-order nonlinear optical responses of centrosymmetric bilayer CrI$_3$

TL;DR

This study predicts large, switchable second-order nonlinear optical responses in antiferromagnetic bilayer CrI3, revealing potential for advanced optoelectronic and photovoltaic applications due to its unique magnetic and nonlinear properties.

Contribution

It demonstrates, through first-principles calculations, that antiferromagnetic bilayer CrI3 exhibits giant, nonreciprocal second-order nonlinear optical responses, a novel finding for centrosymmetric 2D magnetic materials.

Findings

Magnetic SHG, LEO, and photocurrent are comparable or larger than nonmagnetic 2D semiconductors.

NLO responses are nonreciprocal and switchable by magnetization direction.

Predicted NLO coefficients are among the largest for known BPVE materials.

Abstract

Antiferromagnetism (AF) in AB'-stacked centrosymmetric bilayer (BL) CrI$_3$ breaks both spatial inversion ($P$) and time-reversal ($T$) symmetries but maintains the combined $PT$ symmetry, thus inducing novel second-order nonlinear optical (NLO) responses such as second-harmonic generation (SHG), linear electric-optic effect (LEO) and bulk photovoltaic effect (BPVE). In this work, we calculate AF-induced NLO responses of the BL CrI$_3$ based on the density functional theory with the generalized gradient approximation (GGA) plus onsite Coulomb correlation (U), i.e., the GGA+U method. Interestingly, we find that the magnetic SHG, LEO and photocurrent in the AF BL CrI$_3$ are huge, being comparable or even larger than that of the well-known nonmagnetic noncentrosymmetric semiconductors. For example, the calculated SHG coefficients are in the same order of magnitude as that of MoS$_2$ monolayer (ML), the most promising 2D material for NLO devices. The calculated LEO coefficients are almost three times larger than that of MoS$_2$ ML. The calculated NLO photocurrent in the CrI$_3$ BL is among the largest values predicted so far for the BPVE materials. On the other hand, unlike nonmagnetic semiconductors, the NLO responses in the AF BL CrI$_3$ are nonreciprocal and also switchable by rotating magnetization direction. Therefore, our interesting findings indicate that the AF BL CrI$_3$ will not only provide a valuable platform for exploring new physics of low-dimensional magnetism but also have promising applications in magnetic NLO and LEO devices such as frequency conversion, electro-optical switches, and light signal modulators as well as high energy conversion efficiency photovoltaic solar cells.