Symmetrical broken and nonlinear response of Weyl semimetal TaAs influenced by the topological surface states and Weyl nodes

TL;DR

This study investigates the anisotropic linear and nonlinear optical responses of the Weyl semimetal TaAs, revealing the role of topological surface states and Weyl nodes in its unique photoelectric properties and ultrahigh mobility.

Contribution

It provides the first experimental analysis of the anisotropic optical responses in TaAs, linking surface states and Weyl nodes to its nonlinear behavior and high mobility.

Findings

Topological surface states cause anisotropic mobility.

Nonlinear response exhibits saturable behavior with high intensity.

Mobility reaches 10^4 cm^2V^-1s^-1 and is optically tunable.

Abstract

A Weyl semimetal (WSM) features Weyl fermions in its bulk and topological surface states on surfaces, and is novel material hosting Weyl fermions, a kind of fundamental particles. The WSM was regarded as a three-dimensional version of "graphene" under the illusion. In order to explore its promising photoelectric properties and applications in photonics and photoelectronics, here, we study the anisotropic linear and nonlinear optical responses of a WSM TaAs, which are determined by the relationship and balance between its topological surface states and Weyl nodes. We demonstrate that topological surface states which break the bulk symmetry are responsible for the anisotropy of the mobility, and the anisotropic nonlinear response shows saturable characteristic with extremely large saturable intensity. We also find that the mobility is anisotropic with the magnitude of 104 cm2V-1s-1 at room temperature and can be accelerated by the optical field. By analyzing the symmetry, the nonlinear response is mainly contributed by the fermions close to the Weyl nodes, and is related to the Pauli's blocking of fermions, electron-electron interaction. This work experimentally discovers the anisotropic ultrahigh mobility of WSMs in the optical field and may start the field for the applications of WSMs in photonics and photoelectronics.