Colossal magnetoresistance is of great fundamental and technological importance. It mainly exists in manganite and a few other materials. It is conventionally associated with a field-induced spin polarization that drastically reduces spin scattering and electrical resistance.
Ferrimagnetic Mn3Si2Te6 is an intriguing exception to this rule: it exhibits a seven orders of magnitude reduction in resistivity in the ab plane that occurs only when a magnetic polarization is avoided.
The electrical conductivity of Mn3Si2Te6 has now increased by a billion thanks to the discovery of new loop currents that flow along the edges of octahedral cells. The discovery by a group of physicists, including two Georgia Tech researchers, of this new quantum state could lead to a new paradigm for quantum devices and superconductors.
Previously, scientists had come up with the same material. However, it did not fit existing models. So in this study, scientists developed new ideas to understand it, which helped them study related materials that could be used for next-generation magnetic field devices.
The material Mn3Si2Te6 attracted the interest of scientists because of its unique electrical properties. In particular, it has a property called colossal magnetoresistance, an extreme improvement in a material’s electrical conductivity when a magnetic field is applied.
Scientists then tried to understand why the extreme change in conductivity only occurs when the magnetic field is applied perpendicular to the material’s honeycomb-like surface.
Georgia Tech theoretical physicist Itamar Kimchi said: “Our idea smelled promising. Unfortunately, we soon realized that currents between the magnetic manganese ions would be forbidden by symmetry, which was disheartening. However, we then did the symmetry analysis for the octahedral arranged tellurium ions, and for them currents were allowed and could work!
The material looks like a series of two-dimensional honeycombs from above. From the side, it is composed of honeycomb plates. Within each sheet, electrons can move in circular paths around each octahedral cell. The material’s peculiar behavior is due to these looped, circularly flowing currents.
Electrons move counterclockwise and clockwise around the honeycomb cells on their own. Like unregulated traffic, “traffic jams” in material make it challenging for electrons to move through quickly. The material acts more like an insulator, with no method to streamline traffic.
But when a magnetic field is applied perpendicular to the honeycomb-like surface, a “traffic flow” is created. This causes electrons to navigate faster through the loops.
The substance then behaves like a conductor, showing an increase in conductivity of seven orders of magnitude, or one billion percent.
Electric currents applied to the material can also cause it to change from an insulator to a conductor, although that process takes longer. The transition from insulator to conductor can be instantaneous or take minutes.
The research team is hopeful that the material’s sensitivity to currents, tunability and slower form of switching could lead to new developments in current-driven quantum devices, including everything from sensors to computers to secure communications.
Scientists look forward to understanding what makes this material special and what microscopic ingredients are needed for related materials to become useful quantum technologies in the future.
- Zhang, Y., Ni, Y., Zhao, H. et al. Control of chiral orbital currents in a colossal magnetoresistance. Nature 611, 467-472 (2022). DOI: 10.1038/s41586-022-05262-3