Nonlinear effects in topological materials.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nonlinear Optics

Background:

• Materials with linear energy dispersion typically show strong nonlinear optical responses, especially in the terahertz frequency range.
• Topological materials, such as Weyl semimetals (WSMs) and α-T₃ systems, are candidates for exhibiting unique charge transport and nonlinear optical phenomena.

Purpose of the Study:

• To theoretically and numerically investigate charge transport and nonlinear optical effects, including high harmonic generation, in topological materials.
• To explore the dependence of nonlinear optical conductivity on temperature and topological parameters like Weyl point separation and Berry phase.
• To understand how a finite spectral gap influences nonlinear optical effects in these materials.

Main Methods:

• Theoretical modeling and numerical simulations of charge transport.
• Calculation of nonlinear optical conductivity using both semi-classical (velocity operator) and quantum mechanical (density matrix) approaches.
• Analysis of high harmonic generation in Weyl semimetals and α-T₃ systems.

Main Results:

• The nonlinear optical response is shown to be strongly dependent on temperature and topological parameters (Weyl point separation 'b', Berry phase 'ϕ_B').
• A finite spectral gap can significantly modify the nonlinear optical effects.
• Universal behaviors in both linear and nonlinear responses are observed under specific parameter regimes.
• Experimentally accessible critical field values range from 10⁴-10⁵ V/m.

Conclusions:

• The study provides a comprehensive understanding of nonlinear optical phenomena in topological materials.
• Results offer valuable insights for the development of novel nonlinear optoelectronic devices utilizing topological materials.
• The tunability of nonlinear response via temperature and topological parameters highlights their potential for device applications.