High-pressure control of optical nonlinearity in the polar Weyl semimetal TaAs

TL;DR

This study demonstrates that applying pressure to the polar Weyl semimetal TaAs significantly reduces its optical nonlinearity, confirming the link between polar structure and nonlinear optical response and showing pressure as a tuning method.

Contribution

It provides experimental evidence that pressure can modulate the optical nonlinearity in Weyl semimetals by affecting their polar axis, advancing understanding of nonlinear optical properties in these materials.

Findings

SHG yield decreases by over 60% at 20 GPa

Noncentrosymmetric structure persists under pressure

Optical nonlinearity is primarily controlled by the polar axis element

Abstract

The transition metal monopnictide family of Weyl semimetals recently has been shown to exhibit anomalously strong second-order optical nonlinearity, which is theoretically attributed to a highly asymmetric polarization distribution induced by their polar structure. We experimentally test this hypothesis by measuring optical second harmonic generation (SHG) from TaAs across a pressure-tuned polar-to-nonpolar structural phase transition. Despite the high-pressure structure remaining noncentrosymmetric, the SHG yield is reduced by more than 60 % by 20 GPa as compared to the ambient pressure value. By examining the pressure dependence of distinct groups of SHG susceptibility tensor elements, we find that the yield is primarily controlled by a single element that governs the response along the polar axis. Our results confirm a connection between the polar axis and the giant optical nonlinearity of Weyl semimetals and demonstrate pressure as a means to tune this effect $in$ $situ$.