Laser-Induced Hole Coherence and Spatial Self-Phase Modulation in the Anisotropic 3D Weyl Semimetal TaAs.

ABSTRACT

Laser-induced electron coherence is a fascinating topic in manipulating quantum materials. Recently, it has been shown that laser-induced electron coherence in 2D materials can produce a third-order nonlinear optical response spatial self-phase modulation (SSPM), which has been used to develop a novel all-optical switching scheme. However, such investigations have mainly focused on electron coherence, whereas laser-induced hole coherence is rarely explored. Here, the observation of the optical Kerr effect in 3D Weyl semimetal TaAs flakes is reported. The nonlinear susceptibility (χ(3) ) is obtained, which exhibits a surprisingly high value (with χ o n e - l a y e r ( 3 ) \[{\bm{\chi }}_{{\bf one}{\bm{ - }}{\bf layer}}^{{\bf (3)}}\] = 9.9 × 10-9 e.s.u. or 1.4 × 10-16  m2  V-2 at 532 nm). This cannot be explained by the conventional electron mobility, but can be well understood by the unique high anisotropic hole mobility of TaAs. The wind-chime model and χ(3) carrier mobility correlation adequately explain the results, suggesting the crucial role of laser-induced nonlocal ac hole coherence. These observations extend the understanding of SSPM from 2D to 3D quantum materials with anisotropic carrier mobility and from electron coherence to hole coherence.