A team at Rice University uncovered that chiral phonons within a crystal can induce magnetism by aligning electron spins, akin to the effects of a potent magnetic field. This finding challenges traditional physics principles, especially the idea of time-reversal symmetry, heralding a new direction in quantum material research.
Rice University’s exploration reveals chiral phonons’ significant role in quantum advancements.
Quantum materials are seen as the cornerstone for future ultra-fast, energy-efficient information technologies. However, the challenge lies in harnessing their transformative qualities, as the multitude of atoms in solids often overshadows the unique quantum characteristics of electrons.
Chiral Phonons Driving Magnetism
The quantum materials research team at Rice University, led by Hanyu Zhu, discovered that atomic movements in a specific pattern can produce remarkable results: When a rare-earth crystal’s atomic lattice engages in a spiral-like vibration, known as a chiral phonon, it transforms into a magnet.
The study, published in the journal Science, demonstrates that subjecting cerium fluoride to rapid light pulses sets off a dynamic atomic dance. This temporarily aligns electron spins in a manner typically necessitated by a strong magnetic field, considering cerium fluoride’s natural paramagnetic state with random spin orientations even at absolute zero.
Interplay Between Electron Spins and Chiral Movements
Rice materials scientist Boris Yakobson, co-author of the study, explains, “Electrons have magnetic spins, resembling minuscule compass needles within the material, responsive to local magnetic fields. Chirality, or ‘handedness’, should not influence electron spin energies. However, here, the chiral movement within the atomic lattice polarizes these spins as though a substantial magnetic field were applied.”
Boris Yakobson holds the Karl F. Hasselmann Professorship of Engineering at Rice and is a professor of materials science and nanoengineering and chemistry.
The spin alignment effect, although transient, outlasts the light pulse. Since atoms rotate at specific frequencies and move longer at lower temperatures, further experiments varying frequency and temperature corroborate that the magnetization results from the atoms’ collective chiral motion.
Hanyu Zhu is the William Marsh Rice Chair and an assistant professor at Rice in materials science and nanoengineering.
Unforeseen Impact of Atomic Motion
Zhu notes the unexpected impact of atomic motion on electrons, given their lighter and faster nature. Electrons typically adjust to new atomic positions instantaneously, rendering material properties stable regardless of the atoms’ rotational direction. This phenomenon, known as time-reversal symmetry, is a central concept in physics.
The concept that atomic collective motion disrupts time-reversal symmetry is a relatively new idea in physics. Chiral phonons have been experimentally observed in various materials, but their influence on material properties remains an area of active research.
Investigating Spin-Phonon Interactions
The team aimed to quantitatively assess how chiral phonons affect a material’s electrical, optical, and magnetic characteristics. “Considering that spin pertains to electron rotation and phonons to atomic rotation, we anticipated some interaction,” Zhu said. The research focused on a phenomenon termed spin-phonon coupling.
Spin-phonon coupling is crucial in practical applications like data storage on hard disks. Zhu’s group recently showcased a new instance of this coupling in single molecular layers, with atoms moving linearly and affecting spins.
Rice graduate student in applied physics, Jiaming Luo, is the study’s lead author.
The team’s new experiments necessitated driving an atomic lattice into chiral motion, requiring both the selection of a suitable material and the generation of light at the appropriate frequency to initiate the atomic swirl, supported by theoretical calculations from collaborators.
Pioneering Experimental Approaches
Luo, the lead author, explains the challenge of creating the required light pulses for their phonon frequencies, around 10 terahertz. They combined intense infrared lights, adjusting the electric field to interact with the chiral phonons, and employed additional infrared light pulses for observing spin and atomic movements.
Implications for Future Research
This research not only sheds light on spin-phonon coupling but also sets the stage for future investigations in magnetic and quantum materials. Zhu hopes that quantifying the magnetic field effects of chiral phonons will aid in developing protocols to explore new physics in dynamic materials, with the aim of engineering novel materials through external influences like light or quantum fluctuations.
Team members include Tong Lin, Hanyu Zhu, and Jiaming Luo from EQUAL lab at Rice.
The study, titled “Large effective magnetic fields from chiral phonons in rare-earth halides” and led by Jiaming Luo, Tong Lin, Junjie Zhang, Xiaotong Chen, Elizabeth R. Blackert, Rui Xu, Boris I. Yakobson, and Hanyu Zhu, was published on 9 November 2023 in Science.
The research received funding from the National Science Foundation, the Welch Foundation, and the Army Research Office.
Table of Contents
Frequently Asked Questions (FAQs) about Chiral Phonons Magnetism
What is the significance of the Rice University study?
The Rice University study is significant because it demonstrates that chiral phonons in crystals can induce magnetism, challenging traditional physics principles and opening new avenues for research in quantum materials.
What are chiral phonons?
Chiral phonons are a type of atomic movement in crystals characterized by a spiral-like vibration. In this study, they were found to play a crucial role in inducing magnetism in certain materials.
How does this discovery impact quantum materials?
This discovery is important for the field of quantum materials as it provides insights into spin-phonon coupling, a phenomenon that can have practical applications, such as in data storage on hard disks, and could lead to the development of novel materials with unique properties.
What is time-reversal symmetry, and how does this research relate to it?
Time-reversal symmetry is a fundamental concept in physics where the behavior of physical systems remains unchanged when time is reversed. This research challenges time-reversal symmetry by showing that the collective motion of atoms can disrupt it, leading to unexpected effects on material properties.
How was the research conducted?
The research involved subjecting cerium fluoride to ultrafast pulses of light to induce chiral phonons and observe their effects on electron spins. The team used innovative experimental techniques to create the required light pulses and monitor atomic and spin movements.
What are the potential future implications of this research?
The research not only advances our understanding of spin-phonon coupling but also has the potential to inform future studies on magnetic and quantum materials. It may lead to the development of materials engineered through external influences like light or quantum fluctuations.
More about Chiral Phonons Magnetism
- Rice University
- Science Journal
- National Science Foundation
- The Welch Foundation
- Army Research Office
3 comments
thx 4 explainin chiral phonons, wasnt sure wat dey r.
Rice Uni alwys pushin boundries, luv readin abt scienc stuff like dis!
gr8 wrk by Rice uni, dis reseach cud change lotz!