Quantum materials hold the promise of revolutionizing information systems by providing lightning-speed and energy-efficient solutions. Unfortunately, the vast number of atoms in solids often hinders the exploration of their exotic quantum properties. However, researchers at Rice University have made a significant breakthrough in this field. By observing the movement of atoms in circles, they discovered that a chiral phonon – a corkscrew-shaped vibration – can transform a rare-earth crystal into a magnet. Their study, published in Science, reveals that exposing cerium fluoride to ultrafast pulses of light induces a dance of its atoms, momentarily aligning the spins of electrons. This alignment, which would typically require a powerful magnetic field, holds immense potential for future applications.
Cerium fluoride, naturally paramagnetic with randomly oriented spins even at zero temperature, experiences a transformation when subjected to chiral phonons. These phonons create a chiral movement in the atomic lattice, polarizing the spins of the electrons inside the material. Boris Yakobson, a co-author of the study and a materials scientist at Rice University, explains that the chiral movement acts as if a large magnetic field has been applied. Surprisingly, the force that aligns the spins lingers beyond the duration of the light pulse, providing an opportunity for further investigation.
Electrons, being significantly lighter and faster than atoms, usually adapt to new atomic positions immediately. The principle of time-reversal symmetry suggests that material properties would remain unaffected if atoms moved clockwise or counterclockwise in time. However, recent research has shown that the collective motion of atoms can break time-reversal symmetry. This phenomenon, involving chiral phonons, remains relatively poorly understood, making it crucial to explore their impact on material properties, specifically their electrical, optical, and magnetic properties.
The research team, led by Hanyu Zhu, the William Marsh Rice Chair at Rice University, aims to quantitatively measure the effect of chiral phonons on material properties and understand the mechanism behind spin-phonon coupling. Spin-phonon coupling plays a vital role in various real-world applications, such as data storage in hard disks. Earlier this year, Zhu’s group showcased spin-phonon coupling in single molecular layers, where linear motion induced spin vibrations. In their latest experiments, they needed to induce a lattice of atoms to move in a chiral fashion. This required carefully selecting the right material and generating light at the appropriate frequency. Through theoretical computations and experimental techniques, the team succeeded in driving atomic lattices to undergo chiral motion.
Innovative Experimental Design
Creating the necessary light pulses for chiral phonons posed a challenge. With no off-the-shelf light source available at the required frequencies, the researchers mixed intense infrared lights and twisted the electric field to interact with the chiral phonons. They utilized two additional infrared light pulses to monitor the spin and atomic motion, respectively. This innovative experimental design allows for precise control and measurement of the phenomenon under investigation.
The insights gained from this groundbreaking research hold immense potential for the development of dynamic materials and the study of novel physics. Quantitatively measuring the magnetic field generated by chiral phonons opens up new avenues for experimental protocols and further exploration of spin-phonon coupling. By understanding the interplay between the movement of atoms and the behavior of electrons, future advancements in quantum materials and information systems can be accelerated.
The discovery of spin-phonon coupling through chiral phonons not only sheds light on the fundamental properties of materials but also paves the way for transformative applications. Rice University’s research team has successfully aligned the spins of electrons by inducing a chiral motion in atomic lattices. This breakthrough opens up new possibilities for lightning-speed, energy-efficient information systems. By harnessing the power of quantum materials, the future of technology holds immense promise for faster and more efficient computing solutions.