Multiphoton excitation and high-harmonics generation in topological insulator

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Nonlinear Optics

Background:

• Topological insulators (TIs) possess unique surface states with potential for novel electronic and optical phenomena.
• Understanding light-matter interactions in 2D systems is crucial for next-generation electronic and photonic devices.
• Multiphoton processes in confined electron systems are complex and require advanced theoretical frameworks.

Purpose of the Study:

• To develop a microscopic theory for multiphoton interactions between electromagnetic radiation and 2D metallic carriers on 3D TIs.
• To investigate the nonlinear optical response, including interband and intraband transitions, under strong THz fields.
• To explore the generation of high harmonics from the excited 2D electron system.

Main Methods:

• Development of a microscopic theory incorporating many-body Coulomb interactions.
• Numerical solution of a set of coupled integrodifferential equations for interband polarization and carrier occupation.
• Analysis of multiphoton excitation of a Fermi-Dirac sea of 2D massless carriers using a THz pump wave.

Main Results:

• The theory successfully describes the nonlinear interaction of strong electromagnetic waves with 2D metallic carriers.
• Numerical simulations reveal multiphoton interband and intraband transitions within the 2D system.
• Intense radiation of high harmonics is observed in moderately strong pump wave fields.

Conclusions:

• Multiphoton interactions drive significant electronic transitions in 2D metallic states on topological insulators.
• The study demonstrates the capability of generating high harmonics from these systems.
• Findings pave the way for exploring advanced nonlinear optical phenomena in topological materials.