Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI₂

Abstract

Two-dimensional (2D) NbOI 2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI 2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The straindriven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

Tailoring Dispersion Property and Anisotropy of Second-Harmonic Generation by Strain Engineering in Monolayer GeSe

“…Moreover, the uniaxial strain along the b direction appears to have a more substantial impact than that along the a direction. Tailoring the bandgap and electronic transitions within 2D materials allows for controlled absorption and emission of photons, as well as the harmonics generation and other nonlinear processes, ,,, thus enabling a range of applications from photodetection to frequency multiplication.…”

“…In contrast, monolayer group IV monochalcogenides MX (M = Ge, Sn; X = Se, S) with an orthogonal lattice structure demonstrate ferroelectricity-driven valley polarization, independent of magnetism, resulting in linearly polarized light-selective absorption . Additionally, due to symmetry breaking, ferroic materials possess a strong second-order nonlinear optical susceptibility, which endows them with significant potential in the field of nonlinear optics. ,,,,,,− …”

“…For instance, in TMDs/SiP with broken heterointerface symmetry, , a valley-spin-polarized circularly polarized spin photocurrent phenomenon was observed normal to the heterointerface, which could be tuned by gate voltage, demonstrating the triple locking of Berry curvature dipole-spin-valley properties at the heterointerface. Second-order nonlinear optical effects are fundamental in the study of nonlinear physical properties within media, ,,,,,,,,,,− encompassing phenomena such as the photon drag effect, optical rectification, bulk photovoltaic effect, and SHG. ,, As a fundamental second-order nonlinear optical effect, SHG provides a technological platform for characterizing material nonlinear response capabilities, sample uniformity, and crystal symmetry through its spectral, imaging, and anisotropic. ,,,,,,, The current popular methods for controlling SHG can be broadly categorized into external field manipulation , and material structure regulation. ,, …”

Theoretical insight on structure, electronic, and optical properties of two d 0–d 10 electron transition-metal oxyhalides SHG materials

“…Nonlinear optical (NLO) materials have triggered enormous interest, especially using the second harmonic generation (SHG) response to achieve cascaded laser frequency conversion for tunable wavelength laser output [1]. It has a wide range of applications in advanced optical technology of civilian and military equipment such as optical communications and medical surgery [2][3][4].…”