Like all metals, silver, copper and gold are electrical conductors. electrons flow through them Conduct heat and electricity Although gold is a good conductor of electricity under any conditions But some materials can only behave like metallic conductors when the temperature is high enough. at low temperature They act like insulators and do not carry current well. in other words These unusual materials go from acting like a lump of gold to acting like a piece of wood when the temperature drops. Physicists have developed a theory to explain the so-called metal-insulating transformation. But the mechanisms behind the changes are not always clear.
“In some cases, it̵7;s not easy to predict whether the material is metal or an insulator,” explains Yejun Feng, a visiting Caltech associate from the Okinawa Graduate Institute of Science and Technology. “Metals are always good conductors of electricity no matter what. But some other visible metals are insulated for reasons not well understood.” Feng was puzzled at the question for at least five years, others on his team, such as University of Tennessee collaborator David Mandrus. have been thinking about the problem for more than two decades.
Now, a new study from Feng and colleagues is published in nature communicationOffers the cleanest trial proof. But the metal insulator transition theory, proposed 70 years ago by physicist John Slater, follows that the magnetic field, which results in what is known as the “spinning” of electrons in a material, is organized in an orderly fashion. can only drive the transformation of metal insulators in previous experiments Changes in the lattice structure of materials or electron interactions based on their charge are responsible.
“This is a problem that goes back to the theory adopted in 1951, but until now it has been very difficult to find experimental systems that demonstrate spin-to-force interaction. pushed due to confusing factors,” explains co-author Thomas Rosenbaum, a physics professor at Caltech who is also president of the institute and president of Sonja and William Davidow Presidential.
“Slater proposes that when the temperature decreases, The ordered magnetic state prevents electrons from flowing through the material,” Rosenbaum explains. But it turns out that for most materials The electronic interaction of electrons has a greater effect than the magnetic interaction. This makes proving the slater mechanism challenging.”
The research will help answer fundamental questions about the behavior of different materials. And there may be technological applications, for example, in spintronics, where electron spins would form the basis of electrical devices instead of the usual electron charge. Now, “basic questions about metals and insulators will be relevant in the upcoming technological revolution.” happened,” Feng said.
interaction with neighbors
Normally, when something is a good conductor, such as a metal, electrons can move around unobstructed. On the other hand, when using an insulator, the electrons are stuck and cannot move freely. The situation is comparable to that of a community of people, Feng explains. If you think of material as a community and electrons as a member of a household. “Insulators are communities where people don’t want their neighbors to visit because they make them uncomfortable.” However, conductive metals represent. “In close, intimate communities, such as in college dormitories, that neighbors visit freely and often,” he said.
Likewise, Feng uses this metaphor to describe what happens when certain metals become insulators when their temperature drops. “It’s like winter. that people or electrons Stay at home and don’t go out to interact.”
In 1940, physicist Sir Nevill Francis Mott discovered how certain metals can become insulators. His theory, which won the 1977 Nobel Prize in Physics, explains, “Some metals can become insulators when their electronic density is reduced by separating their atoms in a convenient way,” according to a Nobe Prize press release. l In this case, the repulsion force between electrons is behind the change.
In 1951, Slater proposed an alternative mechanism based on the spin-spin interaction. But this idea is difficult to prove due to other processes. of insulating metal transitions, including those proposed by Mott, can overwhelm the slater mechanism, making it difficult to separate.
The real material challenge
In this new study Researchers were able to demonstrate the slater mechanism using a compound that has been studied since 1974 called pyrochlore oxide or Cd2Os2O7. This compound is not affected by other metal-insulating transition mechanisms. The blame mechanism was overshadowed by unexpected experimental challenges. That is the presence of a “domain wall” that divides the material into sections.
“Domain walls are like highways or larger roads between communities,” Feng said. Domain walls can conduct electricity. Although most materials are insulating Although the domain wall started out as an experimental challenge. But it turned out to be crucial to the team’s development of new measurement procedures and techniques to prove the Slater mechanism.
Yishu Wang (Ph.D. ’18), a co-author of Johns, said: “Previous attempts to prove the slater metal-insulated transition theory did not take into account the fact that domain walls are masking. Hopkins University, who has been working on this study, has continued since graduating at Caltech, “by separating domain walls from a large number of insulating materials. We can develop a more complete understanding of the slater mechanism.” Wang previously worked with Patrick Lee, a guest professor at Caltech at MIT, to lay out a fundamental understanding of conductive domain walls using symmetric arguments. This describes how and how electrons in a material respond to changes in the direction of the magnetic field.
“By challenging common assumptions about how conductivity is measured in magnetic materials through a fundamental symmetry argument, We have developed a new tool to examine spintronic devices, which largely depend on cross-domain wall transport,” Rosenbaum said.
“We have developed a method to isolate the influence of domain walls. And then the blame mechanism can be revealed,” Feng said. “It’s like finding a diamond in the rough.”
New quantum switch turns metals into insulators.
Yejun Feng et al. The continuous transformation of metallic insulators driven by spin correlation. nature communication (2021). doi: 10.1038/s41467-021-23039-6
Provided by California Institute of Technology
reference: Magnets Drive Metals to Insulators in New Experiments (2021, June 4) Retrieved June 5, 2021 from https://phys.org/news/2021-06-magnetism-metals-insulators.html.
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