Samarium hexaboride has long puzzled physicists. Now, a team from the University of Michigan has managed to confirm several of its properties, finally closing the decades-old inquiry on the material's classification.
Odd and iridescent, samarium hexaboride is officially classified as a topological insulator, a class of solids that have the ability of metal to conduct electricity across their surface but at the same time rubber-like in such a way that it blocks a current's flow from its interior. What makes samarium hexaboride unusual is that, while it imbibes two distinct properties, it remains the same in chemical composition throughout.
Researchers used a technique known as torque magnetometry to come up with first direct evidence to prove that samarium hexaboride is a topological insulator, observing oscillations in how the material responded to a magnetic field. Their technique also revealed that samarium hexaboride contains Dirac electrons on its surface.
Because samarium hexaboride is a strongly correlated material, its electrons engage more closely with each other, compared to most solids, giving its interior electricity-blocking capabilities.
According to Lu Li, a physics assistant professor and co-author of the study, this deeper understanding of the material opens the possibility that engineers would be able to route electric currents in quantum computers much like how they do in conventional electronics through silicon.
Quantum computers rely on electrons or atoms to carry out memory and processing tasks, offering dramatic boosts in computing power, thanks to their ability to do massive calculations at once.
"Before this, no one had found Dirac electrons in a strongly correlated material. We thought strong correlation would hurt them, but now we know it doesn't. While I don't think this material is the answer, now we know that this combination of properties is possible and we can look for other candidates," said Li.
The possible applications for samarium hexaboride are intriguing, but the researchers are most excited about the basic science they have uncovered.
Jim Allen, a physics emeritus professor who has been studying samarium hexaboride for 30 years, believed that the material was a flawed insulator because of how it behaved. However, he was not able to align his assumptions with the material's other properties.
Samarium hexaboride was hypothesized to be a topological insulator. In 2010, Allen, Cagliyan Kurdak and Kai Sun were able to indirectly show that the hypothesis was correct, but the scientific community needed more solid proof, which University of Michigan researchers were able to provide.
Published in the journal Science, the study received funding support from the U-M Mcubed program, the National Science Foundation and the U.S. Department of Energy.