A representation of the crystal structure of ruthenium trichloride shows the simple honeycomb lattice of ruthenium ions and chlorine ions. The twisted octahedra formed by chlorine around the electron spin of each ruthenium atom are mirror images of each other. This rotation is key to the compound’s unusual behavior, which is evidence that it can contain an example of a quantum spin fluid. Photo credit: Courtesy Arkady Shekhter / National High Magnetic Field Laboratory
Scientists are working on the with a new type of technology Florida State UniversityHeadquartered at the National High Magnetic Field Laboratory has found evidence of a quantum spin fluid, a condition that looks promising as a building block for tomorrow’s quantum computers.
The researchers discovered the exciting behavior when studying the so-called electron spins in the compound ruthenium trichloride. Their results were recently published in the journal Natural physicsshow that electron spins interact via the material and effectively lower the total energy. This type of behavior – consistent with a quantum spin fluid – has been demonstrated in ruthenium trichloride at high temperatures and in high magnetic fields.
Spin fluids, which were first theorized in 1973, remain a mystery. Despite some materials showing promising evidence of this fact, it is extremely difficult to definitively confirm its existence. There is a lot of interest in them, however, as scientists believe that they could be used to design smarter materials in a variety of applications, such as: Quantum computing.
This study emphatically confirms that ruthenium trichloride is a spinning fluid, said physicist Kim Modic, a former doctoral student who worked on the MagLab’s pulsed field facility and is now an assistant professor at the Institute for Science and Technology Austria.
“I think this paper offers a new perspective on ruthenium trichloride and shows a new way of looking for spin fluid signatures,” said Modic, the paper’s lead author.
For decades, physicists have carefully studied the charge on an electron that carries electricity, paving the way for advances in electronics, energy, and other areas. But electrons also have a property called spin. Scientists also want to use the spin aspect of electrons for technology, but the universal behavior of spins is not yet fully understood.
In simple terms, electrons can be thought of as rotating around an axis, like a tip pointed in one direction. In magnetic materials, these spins align either in the same or in the opposite direction. This behavior, known as magnetic order, can be induced or suppressed by temperature or magnetic field. As soon as the magnetic order is suppressed, more exotic states of matter such as quantum spin fluids can arise.
In search of a spinning liquid, the research team looked at ruthenium trichloride. Its honeycomb structure, which has a spin at every point, is like a magnetic version of Graph – another hot topic in condensed matter physics.
“Ruthenium is much heavier than carbon, which leads to strong interactions between the spins,” said MagLab physicist Arkady Shekhter, co-author of the paper.
The team expected that these interactions would increase the magnetic frustration in the material. This is a kind of “three company” scenario, in which two spins pair and the third remains in a magnetic levitation that thwarts the magnetic order. That frustration, the team suggested, could lead to a spin-liquid state. Their data finally confirmed their suspicions.
“It appears that ruthenium trichloride shows signs of the behavior we are looking for at low temperatures and under an applied magnetic field,” Modic said. “The spins are not simply based on the alignment of neighboring spins, but are dynamic – like swirling water molecules – and at the same time maintain a certain correlation between them.”
The results were made possible by a new technique the team developed called resonant torsional magnetometry, which accurately measures the behavior of electron spins in high magnetic fields and could lead to many other new discoveries about magnetic materials, Modic said.
“We don’t really have the workhorse techniques or the analytical machinery to study the excitations of electron spins like we do for charge systems,” Modic said. “The existing methods usually require large samples that may not be available. Our technology is highly sensitive and works with tiny, sensitive samples. This could play a crucial role in this research area. ”
Modic developed the technique as a postdoctoral fellow and then worked with MagLab physicists Shekhter and Ross McDonald, another co-author of the paper, to measure ruthenium trichloride in high magnetic fields.
Their technique was to mount samples of ruthenium trichloride on a cantilever the size of a lock of hair. They used a quartz tuning fork – much like a quartz crystal watch – to vibrate the boom in a magnetic field. Instead of pinpointing the time, they measured the oscillation frequency to study the interaction between the spins in ruthenium trichloride and the applied magnetic field. They took their measurements in two strong magnets in the National MagLab.
“The nice thing about our approach is that it’s a relatively simple setup that allowed us to take our measurements in both a 35-tesla resistive magnet and a 65-tesla pulse field magnet,” said Modic.
The next step in the research will be to examine this system in the world record of the pulsed magnet with 100 Tesla.
“This high magnetic field should allow us to directly observe the suppression of the spin-liquid state, which will help us to learn even more about the inner workings of this compound,” said Shekhter.
Reference: “Scale invariant magnetic anisotropy in RuCl3 at high magnetic fields ”by KA Modic, Ross D. McDonald, JPC Ruff, Maja D. Bachmann, Sie Lai, Johanna C. Palmstrom, David Graf, Mun K. Chan, FF Balakirev, JB Betts, GS Boebinger, Marcus Schmidt, Michael J. Lawler, DA Sokolov, Philip JW Moll, BJ Ramshaw and Arkady Shekhter, October 5, 2020, Natural physics.
DOI: 10.1038 / s41567-020-1028-0
Besides Modic, Shekhter, and McDonald, the other scientists who contributed to this article were: JPC Ruff of Stanford University; Maja D. Bachmann from the Max Planck Institute for Chemical Solid State Physics and Stanford University; She Lai from Los Alamos National Laboratory (LANL), Florida State University (FSU), and Cornell University; Johanna C. Palmstrom of Stanford; David Graf from the National MagLab; Mun Chan, FF Balakirev, and JB Betts from LANL; Greg Boebinger from FSU and the National MagLab; Marcus Schmidt and Dmitry Sokolov from the Max Planck Institute; Michael J. Lawler and Brad Ramshaw of Cornell; and Philip JW Moll from the Max Planck Institute and the Ecole Polytechnique Federal de Lausanne.
This research took place in the National High Magnetic Field Laboratory, the world’s largest and most powerful magnet facility. Located at Florida State University, the University of Florida and the Los Alamos National Laboratory, the interdisciplinary National MagLab, hosts scientists from around the world to conduct basic research in high magnetic fields and improve our understanding of materials, energy and life. The laboratory is funded by the National Science Foundation (DMR-1644779) and the state of Florida.
The Institute for Science and Technology Austria is an international research institute in Vienna that is dedicated to cutting-edge research in the natural and formal sciences.
