Scientists identify a long-sought magnetic state predicted nearly 60 years ago.
Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have discovered a long-predicted magnetic state of matter called an “antiferromagnetic excitonic insulator.”
“Broadly speaking, this is a novel type of magnet,” said Brookhaven Lab physicist Mark Dean, senior author on a paper describing the research just published in Nature Communications. “Since magnetic materials lie at the heart of much of the technology around us, new types of magnets are both fundamentally fascinating and promising for future applications.”
The new magnetic state involves strong magnetic attraction between electrons in a layered material that make the electrons want to arrange their magnetic moments, or “spins,” into a regular up-down “antiferromagnetic” pattern. The idea that such antiferromagnetism could be driven by quirky electron coupling in an insulating material was first predicted in the 1960s as physicists explored the differing properties of metals, semiconductors, and insulators.
“Sixty years ago, physicists were just starting to consider how the rules of quantum mechanics apply to the electronic properties of materials,” said Daniel Mazzone, a former Brookhaven Lab physicist who led the study and is now at the Paul Scherrer Institut in Switzerland. “They were trying to work out what happens as you make the electronic ‘energy gap’ between an insulator and a conductor smaller and smaller. Do you just change a simple insulator into a simple metal where the electrons can move freely, or does something more interesting happen?”
The prediction was that, under certain conditions, you could get something more interesting: namely, the “antiferromagnetic excitonic insulator” just discovered by the Brookhaven team.
Why is this material so exotic and interesting? To understand, let’s dive into those terms and explore how this new state of matter forms.
In an antiferromagnet, the electrons on adjacent atoms have their axes of magnetic polarization (spins) aligned in alternating directions: up, down, up, down and so on. On the scale of the entire material those alternating internal magnetic orientations cancel one another out, resulting in no net magnetism of the overall material. Such materials can be switched quickly between different states. They’re also resistant to information being lost due to interference from external magnetic fields. These properties make antiferromagnetic materials attractive for modern communication technologies.
Next we have excitonic. Excitons arise when certain conditions allow electrons to move around and interact strongly with one another to form bound states. Electrons can also form bound states with “holes,” the vacancies left behind when electrons jump to a different position or energy level in a material. In the case of electron-electron interactions, the binding is driven by magnetic attractions that are strong enough to overcome the repulsive force between the two like-charged particles. In the case of electron-hole interactions, the attraction must be strong enough to overcome the material’s “energy gap,” a characteristic of an insulator.
“An insulator is the opposite of a metal; it’s a material that doesn’t conduct electricity,” said Dean. Electrons in the material generally stay in a low, or “ground,” energy state. “The electrons are all jammed in place, like people in a filled amphitheater; they can’t move around,” he said. To get the electrons to move, you have to give them a boost in energy that’s big enough to overcome a characteristic gap between the ground state and a higher energy level.
In very special circumstances, the energy gain from magnetic electron-hole interactions can outweigh the energy cost of electrons jumping across the energy gap.
Now, thanks to advanced techniques, physicists can explore those special circumstances to learn how the antiferromagnetic excitonic insulator state emerges.
A collaborative team worked with a material called strontium iridium oxide (Sr3Ir2O7), which is only barely insulating at high temperature. Daniel Mazzone, Yao Shen (Brookhaven Lab), Gilberto Fabbris (Argonne National Laboratory), and Jennifer Sears (Brookhaven Lab) used x-rays at the Advanced Photon Source—a DOE Office of Science user facility at Argonne National Laboratory—to measure the magnetic interactions and associated energy cost of moving electrons. Jian Liu and Junyi Yang from the University of Tennessee and Argonne scientists Mary Upton and Diego Casa also made important contributions.
The team started their investigation at high temperature and gradually cooled the material. With cooling, the energy gap gradually narrowed. At 285 Kelvin (about 53 degrees Fahrenheit), electrons started jumping between the magnetic layers of the material but immediately formed bound pairs with the holes they’d left behind, simultaneously triggering the antiferromagnetic alignment of adjacent electron spins. Hidemaro Suwa and Christian Batista of the University of Tennessee performed calculations to develop a model using the concept of the predicted antiferromagnetic excitonic insulator, and showed that this model comprehensively explains the experimental results.
“Using x-rays we observed that the binding triggered by the attraction between electrons and holes actually gives back more energy than when the electron jumped over the band gap,” explained Yao Shen. “Because energy is saved by this process, all the electrons want to do this. Then, after all electrons have accomplished the transition, the material looks different from the high-temperature state in terms of the overall arrangement of electrons and spins. The new configuration involves the electron spins being ordered in an antiferromagnetic pattern while the bound pairs create a ‘locked-in’ insulating state.”
The identification of the antiferromagnetic excitonic insulator completes a long journey exploring the fascinating ways electrons choose to arrange themselves in materials. In the future, understanding the connections between spin and charge in such materials could have potential for realizing new technologies.
Brookhaven Lab’s role in this research was funded by the DOE Office of Science, with collaborators receiving funding from a range of additional sources noted in the paper. The scientists also used computational resources of the Oak Ridge Leadership Computing Facility, a DOE Office of Science user facility at Oak Ridge National Laboratory.
Reference: “Antiferromagnetic Excitonic Insulator State in Sr3Ir2O7” by D. G. Mazzone, Y. Shen, H. Suwa, G. Fabbris, J. Yang, S.-S. Zhang, H. Miao, J. Sears, Ke Jia, Y. G. Shi, M. H. Upton, D. M. Casa, X. Liu, Jian Liu, C. D. Batista and M. P. M. Dean, 17 February 2022, Nature Communications.
Why Is There Something Rather Than Nothing?
A: ) Because Magnetism is an attractive force, not a repulsive force ?
That’s a guess, gravity and allegedly dark matter is also an attractive force.
Isaac Asimov in a book thought it was because there were more protons than electrons in the universe ( thus forming matter )
To prove Magnetism is an attractive force – place two magnets close together freely…what do they do attract to each other or fly apart ?
Babu G. Ranganathan*
SCIENCE SHOWS THAT THE UNIVERSE CANNOT BE ETERNAL because it could not have sustained itself eternally due to the law of entropy (increasing and irreversible net energy decay, even in an open system). Even a hypothetical oscillating universe could not continue to oscillate eternally! Einstein’s General Theory of Relativity shows that space, matter, and time all are physical and all had a beginning. Space even produces particles because it’s actually something, not nothing. What about the Higgs boson (the so-called “God Particle”)? The Higgs boson, even if it existed, would not have created mass from nothing, but rather it would have converted energy into mass. Einstein showed that all matter is some form of energy. Even time had a beginning! Time is not eternal.
The law of entropy doesn’t allow the universe to be eternal. If the universe were eternal, everything, including time and space (which modern science has shown are as physical as mass or matter), would have become totally entropied by now and the entire universe would have ended in a uniform heat death a long, long time ago. The fact that this hasn’t happened already is powerful evidence for a beginning to the universe.
Popular atheistic scientist Stephen Hawking admits that the universe had a beginning and came from nothing but he believes that nothing became something by a natural process yet to be discovered. That’s not rational thinking at all, and it also would be making the effect greater than its cause to say that nothing created something. The beginning had to be of supernatural origin because science teaches us from the First Law of Thermodynamics that natural laws and processes do not have the ability to bring something into existence from nothing.
The supernatural origin of the universe cannot be proved by science but science points to a supernatural intelligence and power for the origin and order of the universe. Where did God come from? Obviously, unlike the universe, God’s nature doesn’t require a beginning.
The disorder in the universe can be explained because of chance and random processes, but the order can be explained only because of intelligence and design.
Gravity may explain how the order found in the precise and orderly courses of thousands of billions of stars is maintained, but gravity cannot explain the origin of that order.
Some evolutionary astronomers believe that trillions of stars crashed into each other leaving surviving stars to find precise orderly orbits in space. Not only is this irrational, but if there was such a mass collision of stars then there would be a super mass residue of gas clouds in space to support this hypothesis. The present level of residue of gas clouds in space doesn’t support the magnitude of star deaths required for such a hypothesis. And, as already stated, the origin of stars cannot be explained by the Big Bang because of the reasons mentioned above. It’s one thing to say that stars may decay and die into random gas clouds, but it is totally different to say that gas clouds form into stars.
JUST BECAUSE SCIENCE CAN EXPLAIN how an airplane works doesn’t mean that no one designed or made the airplane. And just because science can explain how life or the universe works doesn’t mean there was no Designer and Maker behind them.
Natural laws may explain how the order in the universe works and operates, but mere undirected natural laws cannot explain the origin of that order. Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells from raw materials such as amino acids and other chemicals, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.
WHAT IS SCIENCE? Science simply is knowledge based on observation. No human observed the universe coming by chance or by design, by creation or by evolution. These are positions of faith. The issue is which faith the scientific evidence best supports.
Even the father of Chaos theory admitted that the “mechanisms” existing in the non-living world allow for only very rudimentary levels of order to arise spontaneously (by chance), but not the kind or level of order we find in the structures of DNA, RNA, and proteins. Yes, individual amino acids have been shown to come into existence by chance but not protein molecules which require that the various amino acids be in a precise sequence just like the letters found in a sentence.
Some things don’t need experiment or scientific proof. In law there is a dictum called prima facie evidence. It means “evidence that speaks for itself.”
An example of a true prima facie would be if you discovered an elaborate sand castle on the beach. You don’t have to experiment to know that it came by design and not by the chance forces of wind and water.
If you discovered a romantic letter or message written in the sand, you don’t have to experiment to know that it was by design and not because a stick randomly carried by wind put it there. You naturally assume that an intelligent and rational being was responsible.
It’s interesting that Carl Sagan would have acknowledged sequential radio signals in space as evidence of intelligent life sending them, but he wouldn’t acknowledge the sequential structure of molecules in DNA (the genetic code) as evidence of an intelligent Cause. Read my popular Internet article, HOW DID MY DNA MAKE ME.
I encourage all to read my popular Internet articles:
NATURAL LIMITS TO EVOLUTION
HOW FORENSIC SCIENCE REFUTES ATHEISM
Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)
Author of popular Internet article, TRADITIONAL DOCTRINE OF HELL EVOLVED FROM GREEK ROOTS
*I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.