Moore Foundation grantees at Johns Hopkins University and Rutgers University have shed light on a fundamental question in physics: what connects the everyday, classical behavior of physical systems with the quantum world, which plays by an entirely different set of rules?
"We found a particular material that is straddling these two regimes," said N. Peter Armitage, an associate professor of physics at the Johns Hopkins University. "Usually, we think of quantum mechanics as a theory of small things, but in this system quantum mechanics is appearing on macroscopic length scales. The experiments are made possible by unique instrumentation developed in my laboratory."
Armitage led this research, which involved six scientists from Johns Hopkins and Rutgers University, including Seongshik Oh, an investigator in the foundation's Emergent Phenomena in Quantum Systems initiative. The findings were recently published in Science magazine.
The team studied topological insulators — materials that can carry electrical current on their surface without resistance at room temperature. Topological materials were the subject of this year's Nobel Prize in Physics.
One of the long-standing predictions regarding topological insulators is the magnetoelectric effect, a coupling between a material's magnetic and electric properties. Thanks to this coupling, the dynamics of electrons inside topological insulators are modified to resemble quantum mechanical behavior.
Armitage, Oh and their colleagues used high-frequency terahertz light to observe signatures of these unusual properties in a thin film of a material made of the elements bismuth and selenium. They detected tiny changes to the polarization of terahertz light after it passed through the thin film, confirming the expected fingerprints of a quantum state of matter.
In particular, they found as the light was transmitted through the material, the wave rotated a specific amount, which is related to physical constants that can usually only be measured in atomic scale experiments.
These results add to scientists' understanding of topological insulators, but also may contribute to understanding the relationship between the macroscopic classical world and the quantum world.
Read the full article here.