Second-harmonic generation and linear electro-optical coefficients of BN nanotubes

TL;DR

This study uses ab initio methods to analyze the second-order nonlinear optical properties of BN nanotubes, revealing they have significantly larger nonlinear coefficients than bulk BN, making them promising for optical applications.

Contribution

It provides the first comprehensive ab initio calculations of second-harmonic generation and electro-optical coefficients for various BN nanotubes, including single- and double-walled structures.

Findings

BN nanotubes exhibit large second-order nonlinear optical coefficients.

Double-walled BN nanotubes show reduced nonlinear coefficients due to interwall interactions.

Spectral features of nonlinear response are correlated with linear dielectric functions.

Abstract

A systematic {\it ab initio} study of the second-order nonlinear optical properties of BN nanotubes within density functional theory in the local density approximation has been performed. Highly accurate full-potential projector augmented-wave method was used. Specifically, the second-harmonic generation ($\chi_{abc}^{(2)}$) and linear electro-optical ($r_{abc}$) coefficients of a large number of the single-walled zigzag, armchair and chiral BN nanotubes (BN-NT) as well as the double-walled zigzag (12,0)@(20,0) BN nanotube and the single-walled zigzag (12,0) BN-NT bundle have been calculated. Importantly, unlike carbon nanotubes, both the zigzag and chiral BN-NTs are found to exhibit large second-order nonlinear optical behavior with the $\chi_{abc}^{(2)}$ and $r_{abc}$ coefficients being up to thirty times larger than that of bulk BN in both zinc-blende and wurtzite structures, indicating that BN-NTs are promising materials for nonlinear optical and opto-electric applications. Though the interwall interaction in the double-walled BN-NTs is found to reduce the second-order nonlinear optical coefficients significantly, the interwall interaction in the single-walled BN-NT bundle has essentially no effect on the nonlinear optical properties. The prominant features in the spectra of $\chi_{abc}^{(2)}(-2\omega,\omega,\omega)$ of the BN-NTs are suscessfully correlated with the features in the linear optical dielectric function $\epsilon (\omega)$ in terms of single-photon and two-photon resonances.