Solid-state Nonlinear Terahertz Magnon-Polaritonics
Abstract
The primary research objectives in this project are the development and use of a solid-state platform for nonlinear spectroscopy and signal processing involving collective spin waves, i.e. magnons, that interact with light to form coupled terahertz-frequency excitations called magnon-polaritons. Magnon-polaritons combine the magnetization properties of magnons with the propagation speed of light, offering unique possibilities for ultrahigh-speed magnonic signal processing. Such prospects would require methods for facile signal generation, guidance, and readout, and also nonlinear functionalities through which input signals could interact to generate new output signals. We have developed a solid-state planar waveguide platform for generation, propagation, and readout of terahertz-frequency polaritonic signals, and we have shown that magnon-polaritons can be included as signal components. We have separately demonstrated nonlinear interactions among magnons, outside of any polaritonic platform and without strong coupling between the magnons and light. In this project we will extend our THz polaritonics platform to include nonlinear interactions of magnon-polaritons. Fundamental research will be conducted to elaborate the extent and types of magnon-polariton nonlinearities. The results will indicate the most promising prospects for nonlinear magnonic signal processing applications. The main technical approach will be to use slabs of ferroelectric (FE) lithium niobate or lithium tantalate crystals, typically 30-50 microns thick, as THz waveguides in which the signals are admixtures of light and highly polar lattice vibrations, i.e. phonon-polaritons. These can be attached to similar slabs of antiferromagnetic (AFM) crystals such as erbium or yttrium orthoferrite to make hybrid FE/AFM planar waveguides that support magnon-polaritons. We will conduct nonlinear THz spectroscopy, in particular two-dimensional THz spectroscopy in which signals due to nonlinear interactions appear at unique frequency combinations that reveal the nature of the nonlinearities. For example, signals mightarise at the excitation frequency of one magnon-polariton mode and the detection frequency of another magnon-polariton mode, showing that magnon-polaritons of the second mode were generated from those of the first. Sum-frequency signals may also appear, showing that excitations of two different magnon-polariton modes can interact to produce a correlated double-excitation state. These and other nonlinear signals will reveal the mechanisms of nonlinear magnon-polariton interactions and will indicate the most promising nonlinear signal processing functionalities. Nonlinearities may be optimized through fabrication of THz elements in the polaritonics platform, mainly through femtosecond laser machining or deposition of features onto waveguide surfaces. For example, THz resonant cavities can be constructed to enhance the magnon interactions with light, resulting in formation of cavity magnon-polariton modes with distinct frequencies. Deposition of semiconductors with nonlinear electronic responses may confer enhanced nonlinearity to magnon-polaritons. Acoustic strain may be used to modulate magnon-polariton properties and nonlinearities. Finally, multiferroics or other material classes that support magnon modes may be substituted for antiferromagnetic materials in order to broaden the range of nonlinearinteractions involving magnon-polaritons. Magnonic signal processing is expected to operate with extremely low power and at extremely high speeds, i.e. terahertz bandwidths. These are capabilities of great interest to the Navy and more broadly throughout the DoD and beyond. Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 13, 2025
- Source ID
- N000142512089
Entities
People
- Keith A. Nelson
Organizations
- Massachusetts Institute of Technology
- Office of Naval Research
- United States Navy