Frequency renormalization and its effects in nonlinear phononics withQRQIR2-type coupling

Area of Science:

• Condensed matter physics
• Nonlinear optics
• Materials science

Background:

• Phonon-electron interactions are crucial for understanding material properties.
• Nonlinear optical phenomena offer pathways to control material behavior.
• Dynamical multiferroicity presents opportunities for novel device functionalities.

Purpose of the Study:

• Investigate a two-phonon system with specific coupling forms (QRQ²IR and QR(Q²IR,x-Q²IR,y)).
• Obtain analytic results for phonon displacements and frequencies using perturbation theory.
• Explore the potential for simultaneous Raman rectification and magnetization.

Main Methods:

• Perturbation method applied to a two-phonon system.
• Analysis of frequency renormalization in infrared (IR) active modes.
• Simulation of resonant pumping with elliptically or linearly polarized ultrashort mid-IR pulses.

Main Results:

• Frequency renormalization of IR active modes leads to saturation of Raman mode rectification at high pump fields.
• Degenerate IR modes with specific coupling exhibit frequency splitting under resonant pumping.
• Simultaneous Raman rectification and magnetization are achieved.

Conclusions:

• The study reveals a dynamical nonlinear phononics effect beyond first-principles calculations.
• Dynamical multiferroicity is extended to systems with QR(Q²IR,x-Q²IR,y) coupling.
• The developed method is applicable to higher-order couplings, with amplitude saturation suggesting future research directions.