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 <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics> <mrow><msubsup><mi>χ</mi> <mrow><mi>o</mi> <mi>n</mi> <mi>e</mi> <mo>-</mo> <mi>l</mi> <mi>a</mi> <mi>y</mi> <mi>e</mi> <mi>r</mi></mrow> <mrow><mo>(</mo> <mn>3</mn> <mo>)</mo></mrow> </msubsup> </mrow> <annotation>\[{\bm{\chi }}_{{\bf one}{\bm{ - }}{\bf layer}}^{{\bf (3)}}\]</annotation></semantics> </math> = 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.