Searching for a fundamental constituent of the universe

Although no one has visually detected axions, researchers have theorized their existence as a way to address significant queries within particle physics, particularly regarding dark matter, an enigmatic substance that constitutes the majority of the universe’s mass. Validating axions could yield profound insights into the universe’s historical context and composition.

Recently, in a pioneering experiment, a collaboration of scientists spearheaded by Harvard and King’s College London has taken a substantial stride toward utilizing quasiparticles for the search of axions, which are theorized to constitute dark matter. Their results, published in Nature, pave the way for harnessing quasiparticles in the quest for dark matter and advancing new quantum technologies.

“Axion quasiparticles can serve as simulations of axion particles, potentially acting as detectors for the actual particles,” stated senior co-author Suyang Xu, assistant professor of chemistry. “When a dark matter axion interacts with our material, it energizes the quasiparticle, and by identifying this reaction, we can validate the presence of the dark matter axion.”

Frank Wilczek, the Nobel laureate who initially introduced axions, acknowledges these discoveries as a critical leap forward in the exploration of these particles.

“The existence of axions as fundamental particles that enhance physics’ primary equations and embody cosmological dark matter is still debated,” Wilczek remarked. “However, owing to these ingenious new experiments, we can now confirm that nature employs the fundamental concepts. Axions now join the ranks of holes, phonons, plasmons, and other ‘quasiparticles’ that emerge as fundamental components of matter, ripe for new scientific and technological innovations.”

The experimental efforts were led by Jian-Xiang Qiu, a student in the Harvard Griffin Graduate School of Arts and Sciences’s Xu lab. Collaborators on the research included Yu-Fei Liu, Anyuan Gao, Christian Tzschaschel, Houchen Li, Damien Berube, Thao Dinh, Tianye Huang, along with an international cohort from King’s College, UC Berkeley, Northeastern University, among other institutions.

The researchers employed manganese bismuth telluride, a substance celebrated for its distinctive electronic and magnetic properties. By structuring this material into a 2D crystal format, they created an optimal platform for facilitating axion quasiparticles. This involved precise nano-fabrication engineering, where the material was meticulously layered to enhance its quantum attributes.

“Our laboratory has engaged with this intriguing material for nearly five to six years; it presents a rich material platform, albeit challenging to manipulate,” remarked lead author Qiu. “Due to its sensitivity to air, we had to exfoliate it down to several atomic layers to adequately adjust its properties.”

Within a highly regulated environment, the team coaxed the axion quasiparticles to reveal their dynamic characteristics in manganese bismuth telluride. To achieve this delicate endeavor, they employed an array of sophisticated methodologies, including ultrafast laser optics. Innovative measuring instruments enabled them to accurately observe the movements of axion quasiparticles, converting a theoretical concept into a tangible phenomenon.

By demonstrating the coherent behaviors and complex dynamics of axion quasiparticles, the researchers not only validated long-standing theoretical concepts within condensed-matter physics but also established the foundation for prospective technological advancements. For instance, the axion polariton represents a novel form of light-matter interaction that could introduce cutting-edge optical applications.

In the domains of particle physics and cosmology, this fresh observation of the axion quasiparticle may serve as a dark-matter detector, conceptualized by the researchers as a “cosmic car radio,” potentially evolving into the most precise dark-matter detector to date.

Dark matter continues to be one of the most significant enigmas in physics, accounting for approximately 85 percent of the universe’s mass without detection. By tuning into specific radio frequencies produced by axion particles, the research team aspires to capture dark-matter signals that previous technologies have missed. They speculate this could facilitate the identification of dark matter within 15 years.

“This is an extraordinarily exhilarating time to be involved in dark-matter research. Currently, there are as many papers being published concerning axions as there were regarding the Higgs-Boson a year prior to its discovery,” stated senior co-author David Marsh, a lecturer at King’s College London. “Experiments theorized that axions emitted a frequency in 1983, and we now understand how to tune into it — we are closing in on the axion rapidly.”

Xu expresses confidence that the diverse strategies employed by the team contributed to their pioneering achievements.

“Our research is enabled by a highly interdisciplinary approach that encompasses condensed-matter physics, material chemistry, and high-energy physics,” Xu indicated. “This showcases the potential of quantum materials within particle physics and cosmology.”

Looking ahead, the researchers intend to delve deeper into the characteristics of axion quasiparticles while enhancing experimental conditions for improved accuracy.

“Our future objective is undoubtedly to conduct experiments that scrutinize axion dark matter, which would be immensely advantageous for the entire particle physics community invested in axions,” commented senior co-author Jan Schütte Engel, a physicist at UC Berkeley.

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This research has received partial funding from the U.S. Department of Energy, the Air Force Office of Scientific Research, and the National Science Foundation.