Periodic Reporting for period 1 - ASTRAL (Antiferromagnetic Spin Transport With Relativistic Waves)
Période du rapport: 2023-01-01 au 2025-06-30
The rapid expansion of digital technologies is driving an increasing demand for faster and more energy-efficient computing. While electronic and optical approaches have pushed data transfer and processing speeds to new limits, they still face significant power dissipation and scalability constraints. Magnonics, which processes information using spin waves (SWs) instead of electric currents, offers a promising alternative with lower energy losses and high-speed operation.
So far, most magnonic systems rely on ferromagnets (FMs)—materials where atomic spins (tiny magnetic moments) all align in the same direction. While this allows for efficient SW generation and control, FMs operate in the GHz range, limiting their speed. In contrast, antiferromagnets (AFMs) have spins that alternate in opposite directions, cancelling their overall magnetization while enabling much higher-frequency terahertz (THz) spin waves. AFMs also switch 1,000 times faster than FMs, making them ideal for ultrafast computing. Recent breakthroughs have demonstrated THz SW generation and control in AFMs, but a key missing piece remains—THz magnetic nonlinearities. These nonlinearities, essential for SW interaction, amplification, and information processing, require fast and large-amplitude spin perturbations, which have yet to be realized.
ASTRAL aims to enter the nonlinear regime of THz magnonics by generating a new physical object—ultrashort, large-amplitude SW pulses. Similar to femtosecond laser pulses in optics, these pulses can propagate over long distances while unlocking nonlinear interactions between pulses, other SWs, and even macroscopic spin textures. AFMs provide an ideal medium for this approach, as their intrinsically high SW frequencies naturally reach the THz range and, like light waves in vacuum, follow a linear (relativistic) dispersion relation. This allows a broadband wavepacket of coherent SWs to be compressed into an ultrashort SW pulse, consisting of few-cycle, large-amplitude spin oscillations.
To achieve this, ASTRAL will leverage ultrafast laser pulses to initiate and control spin dynamics, aiming to convert femtosecond laser pulses into large-amplitude ultrashort SW pulses.
ASTRAL addresses four key objectives:
• Developing new experimental protocols for generating SW pulses with sub-1 ps durations and long propagation lengths (>1 µm).
• Designing advanced imaging techniques to visualize SW pulses in real space and track their evolution with high temporal and spatial resolution.
• Entering the nonlinear SW regime by demonstrating magnon-magnon interactions and energy redistribution mechanisms in AFMs.
• Using SW pulses to manipulate AFM domains and spin textures, paving the way for ultrafast spintronic devices.
By achieving these objectives, ASTRAL will establish the foundation for revolutionary new computing technologies, bringing THz magnonics closer to real-world applications in energy-efficient, high-speed information processing.
So far, most magnonic systems rely on ferromagnets (FMs)—materials where atomic spins (tiny magnetic moments) all align in the same direction. While this allows for efficient SW generation and control, FMs operate in the GHz range, limiting their speed. In contrast, antiferromagnets (AFMs) have spins that alternate in opposite directions, cancelling their overall magnetization while enabling much higher-frequency terahertz (THz) spin waves. AFMs also switch 1,000 times faster than FMs, making them ideal for ultrafast computing. Recent breakthroughs have demonstrated THz SW generation and control in AFMs, but a key missing piece remains—THz magnetic nonlinearities. These nonlinearities, essential for SW interaction, amplification, and information processing, require fast and large-amplitude spin perturbations, which have yet to be realized.
ASTRAL aims to enter the nonlinear regime of THz magnonics by generating a new physical object—ultrashort, large-amplitude SW pulses. Similar to femtosecond laser pulses in optics, these pulses can propagate over long distances while unlocking nonlinear interactions between pulses, other SWs, and even macroscopic spin textures. AFMs provide an ideal medium for this approach, as their intrinsically high SW frequencies naturally reach the THz range and, like light waves in vacuum, follow a linear (relativistic) dispersion relation. This allows a broadband wavepacket of coherent SWs to be compressed into an ultrashort SW pulse, consisting of few-cycle, large-amplitude spin oscillations.
To achieve this, ASTRAL will leverage ultrafast laser pulses to initiate and control spin dynamics, aiming to convert femtosecond laser pulses into large-amplitude ultrashort SW pulses.
ASTRAL addresses four key objectives:
• Developing new experimental protocols for generating SW pulses with sub-1 ps durations and long propagation lengths (>1 µm).
• Designing advanced imaging techniques to visualize SW pulses in real space and track their evolution with high temporal and spatial resolution.
• Entering the nonlinear SW regime by demonstrating magnon-magnon interactions and energy redistribution mechanisms in AFMs.
• Using SW pulses to manipulate AFM domains and spin textures, paving the way for ultrafast spintronic devices.
By achieving these objectives, ASTRAL will establish the foundation for revolutionary new computing technologies, bringing THz magnonics closer to real-world applications in energy-efficient, high-speed information processing.
In its first two years, ASTRAL has successfully established the necessary infrastructure for studying spin-wave pulses.
A key achievement is the desing, comissioning and installation of a unique laser source capable of operating at different wavelengths and variable repetition rates, allowing optimization between per-pulse power and pulse statitstics. This flexibility enables unprecedented flexibility necessary to identify the best material systems for observing the spin-wave pulse.
ASTRAL has also assembled a dedicated research team, consisting of one PhD student and a postdoctoral researcher, who have already made significant progress toward the project's goals. Together, we confirmed that optical pumping of intense charge-transfer rabove-bandgap transitions in insulating antiferromagnets serves as a universal mechanism for ultrabroadband spin-wave packet generation across a wide range of oxides. Previously, this mechanism was known only for a single antiferromagnetic material system. Additionally, we identified materials where the spin-wave coherence length—and consequently, the spin-wave pulse length—can reach up to 10 µm, making them highly promising for our research.
Using electron-beam lithography, we also successfully nanopatterned the surfaces of antiferromagnets to create grating couplers for sub-wavelength localization of optical excitation. The further research will focus on detecting THz spin waves with precisely engineered wave properties.
Finally, we employed a novel double-pump technique to demonstrate that a uniform spin precession can be upconverted into propagating, nonuniform spin waves through the intrinsic nonlinearity of the antiferromagnetic state—a phenomenon that had not been identified before.
These achievements mark significant progress toward unlocking the nonlinear regime of THz magnonics, bringing ASTRAL closer to its goal of revolutionizing energy-efficient, ultrafast spin-wave computing.
A key achievement is the desing, comissioning and installation of a unique laser source capable of operating at different wavelengths and variable repetition rates, allowing optimization between per-pulse power and pulse statitstics. This flexibility enables unprecedented flexibility necessary to identify the best material systems for observing the spin-wave pulse.
ASTRAL has also assembled a dedicated research team, consisting of one PhD student and a postdoctoral researcher, who have already made significant progress toward the project's goals. Together, we confirmed that optical pumping of intense charge-transfer rabove-bandgap transitions in insulating antiferromagnets serves as a universal mechanism for ultrabroadband spin-wave packet generation across a wide range of oxides. Previously, this mechanism was known only for a single antiferromagnetic material system. Additionally, we identified materials where the spin-wave coherence length—and consequently, the spin-wave pulse length—can reach up to 10 µm, making them highly promising for our research.
Using electron-beam lithography, we also successfully nanopatterned the surfaces of antiferromagnets to create grating couplers for sub-wavelength localization of optical excitation. The further research will focus on detecting THz spin waves with precisely engineered wave properties.
Finally, we employed a novel double-pump technique to demonstrate that a uniform spin precession can be upconverted into propagating, nonuniform spin waves through the intrinsic nonlinearity of the antiferromagnetic state—a phenomenon that had not been identified before.
These achievements mark significant progress toward unlocking the nonlinear regime of THz magnonics, bringing ASTRAL closer to its goal of revolutionizing energy-efficient, ultrafast spin-wave computing.
The implementation of the double-pump excitation technique, using a time-delayed sequence of femtosecond UV pulses, has proven to be a game changer, delivering results in magnonics that go beyond the state of the art. This approach effectively excites broadband spin-wave packets and has revealed that canted antiferromagnetic spin configurations enable a previously unknown mechanism for converting a magnon at the center of the Brillouin zone into propagating finite-k magnons. This conversion occurs through nonlinear magnon-magnon interactions activated by an ultrafast laser pulse. The discovery provides fundamental insights into nonlinear spin-wave dynamics and opens new pathways for controlling magnons in antiferromagnetic materials.