An interdisciplinary team led by Boston College physicists has discovered a new particle – or previously undetectable quantum excitation – known as the Higgs axial mode, a magnetic relative of the mass-defining Higgs Boson particle, reports the team in the journal Nature. Credit: Nature
Materials that contain the axial Higgs mode could serve as quantum sensors to assess other quantum systems and help answer lingering questions in particle physics.
According to Standard Model of Particle Physics, scientists’ current best theory for describing the most basic building blocks of the universe, particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter. Force-carrying particles, which belong to a larger group of bosons, influence quarks and leptons.
Despite the success of the Standard Model in explaining the universe, it has its limitations. Dark matter and dark energy are two examples, and it’s possible that new particles, yet to be discovered, may eventually solve these puzzles.
Today, an interdisciplinary team of scientists led by physicists from Boston College announced that they have discovered a new particle – or previously undetectable quantum excitation – known as the axial Higgs mode, a magnetic relative of the boson particle. Higgs which defines mass. The team published their report today (June 8, 2022) in the online edition of the journal Nature.
The detection ten years ago of the long-sought Higgs boson has become essential to understanding mass. Unlike its relative, the axial Higgs mode has a magnetic moment, and that requires a more complex form of theory to explain its properties, said Boston College physics professor Kenneth Burch, co-lead author of the “Axial Higgs Mode Detected by Quantum Pathway Interference in RTe3.”
Theories that predicted the existence of such a mode have been invoked to explain “black matter“, the nearly invisible material that makes up much of the universe, but only reveals itself through gravity,” Burch said.
The Higgs boson is the fundamental particle associated with the Higgs field, a field that gives mass to other fundamental particles such as electrons and quarks. The mass of a particle determines how much it resists changing speed or position when it encounters a force.
Whereas The Higgs boson was revealed by experiments in a massive particle collider, the team focused on RTe3or rare-earth tritelluride, a well-studied quantum material that can be examined at room temperature in an experimental “tabletop” format.
“It’s not every day that you find a new particle on your table,” Burch said.
RTE3 has properties that mimic the theory that produces the axial Higgs mode, Burch said. But the central challenge in searching for Higgs particles in general is their weak coupling to experimental probes, such as beams of light, he said. Likewise, revealing the subtle quantum properties of particles typically requires quite complex experimental setups, including huge magnets and high-powered lasers, while cooling samples to extremely cold temperatures.
The team reports that they overcame these challenges through the unique use of light scattering and the appropriate choice of quantum simulator, essentially a material that mimics the desired properties for study.
Specifically, the researchers focused on a compound long known to possess a “charge density wave,” a state in which electrons self-organize with periodic density in space, Burch said. .
The fundamental theory of this wave mimics components of the Standard Model of particle physics, he added. However, in this case the charge density wave is quite peculiar, it emerges well above room temperature and involves modulation of both charge density and atomic orbits. This allows the Higgs boson associated with this charge density wave to have additional components, namely it could be axial, meaning it contains angular momentum.
In order to reveal the subtle nature of this mode, Burch explained that the team used light scattering, where a laser is directed at the material and can change color as well as polarization. The color change results from light creating the Higgs boson in the material, while the polarization is sensitive to the symmetry components of the particle.
Moreover, with the proper choice of forward and outward polarization, the particle could be created with different components – such as an absent magnetism or an upward pointing component. Exploiting a fundamental aspect of quantum mechanics, they used the fact that for a configuration, these components cancel each other out. However, for a different configuration, they add.
“So we were able to reveal the hidden magnetic component and prove the discovery of the first axial Higgs mode,” Burch said.
“Axial Higgs detection has been predicted in high-energy particle physics to explain dark matter,” Burch said. “However, this has never been observed. Its appearance in a condensed matter system is quite surprising and announces the discovery of a new state of broken symmetry which had not been predicted. Unlike the extreme conditions generally required to observe new particles, this was done at room temperature in a tabletop experiment where we get quantum mode control by simply changing the polarization of light.
Burch said the seemingly accessible and simple experimental techniques deployed by the team can be applied to study in other fields.
“A lot of these experiments were done by an undergraduate student in my lab,” Burch said. “The approach can be directly applied to the quantum properties of many collective phenomena, including modes in superconductors, magnets, ferroelectrics, and charge density waves. Moreover, we bring the study of quantum interferences in phase-correlated and/or topological materials to room temperature by overcoming the difficulty of extreme experimental conditions.
In addition to Burch, co-authors of the Boston College report included undergraduate student Grant McNamara, recent doctoral student Yiping Wang and postdoctoral researcher Md Mofazzel Hosen. Wang won the American Physical Society’s top dissertation in magnetism, in part for her work on the project, Burch said.
Burch said it was crucial to tap into the wide range of expertise among researchers from British Columbia, Harvard University,[{” attribute=””>Princeton University, the University of Massachusetts, Amherst, Yale University, University of Washington, and the Chinese Academy of Sciences.
“This shows the power of interdisciplinary efforts in revealing and controlling new phenomena,” Burch said. “It’s not every day you get optics, chemistry, physical theory, materials science and physics together in one work.”
Reference: “Axial Higgs mode detected by quantum pathway interference in RTe3” by Yiping Wang, Ioannis Petrides, Grant McNamara, Md Mofazzel Hosen, Shiming Lei, Yueh-Chun Wu, James L. Hart, Hongyan Lv, Jun Yan, Di Xiao, Judy J. Cha, Prineha Narang, Leslie M. Schoop and Kenneth S. Burch, 8 June 2022, Nature.
DOI: 10.1038/s41586-022-04746-6
Funding: U.S. Department of Energy
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