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

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.

Automated summary

The transition metal monopnictide family of Weyl semimetals has been found to possess strong second-order optical nonlinearity, which is attributed to the asymmetric polarization distribution induced by the polar structure. In this study, we experimentally demonstrated that the optical second harmonic generation (SHG) from TaAs decreases by more than 60% under pressure, despite the high-pressure structure remaining noncentrosymmetric. Our results indicate that the SHG yield is primarily controlled by a single element along the polar axis. This study confirms the connection between the polar axis and the giant optical nonlinearity of Weyl semimetals, and shows that pressure can be used to tune this effect.