Colossal magnetoresistance is of great fundamental and technological significance. It exists mainly in manganites and a few other materials. It is conventionally associated with a field-induced spin polarization that drastically reduces spin scattering and electric resistance.
Ferrimagnetic Mn3Si2Te6 is an intriguing exception to this rule: it exhibits a seven-order-of-magnitude reduction in ab plane resistivity that occurs only when a magnetic polarization is avoided.
The electric conductivity of Mn3Si2Te6 has now been increased by a billion times thanks to the discovery of novel looping currents that flow around the edges of octahedral cells. The discovery made by a group of physicists, including two Georgia Tech researchers, 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 any preexisting models. Hence, scientists in this study developed new ideas to understand it, which helped them study related materials that could be used for next-generation magnetic field devices.
The Mn3Si2Te6 material attracted scientists’ interest because of its unique electrical properties. In particular, it has a property called colossal magnetoresistance, an extreme enhancement in a material’s electrical conductivity when a magnetic field is applied.
Scientists then set out to understand why the extreme change in conductivity only happens when the magnetic field is applied perpendicularly to the honeycomb-like surface of the material.
Georgia Tech theoretical physicist Itamar Kimchi said, “Our idea smelled promising. Unfortunately, we quickly realized that currents between the magnetic manganese ions would be forbidden by symmetry, which was discouraging. However, we then did the symmetry analysis for the octahedrally arranged tellurium ions, and, for them, currents were symmetry-allowed and could work out!”
The material looks like a series of two-dimensional honeycombs from above. From the side, it is composed of honeycomb sheets. Within each sheet, electrons can move in circular paths around each octahedral cell. The peculiar behavior of the material is due to these looping, circularly flowing currents.
Electrons, on their own, move anticlockwise and clockwise around the honeycomb cells. Like unregulated traffic, “traffic jams” in material make it challenging for electrons to pass swiftly through it. The material behaves more like an insulator, with no method to streamline traffic.
But when applying a magnetic field perpendicular to the honeycomb-like surface, a “flow of traffic” is established. This causes electrons to navigate the loops more quickly.
The substance then behaves as a conductor and exhibits a conductivity increase of seven orders of magnitude, or a billion percent.
Electrical 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 might happen instantly or take minutes.
The research team is hopeful that the material’s sensitivity to currents, tuneability, and slower form of switching could lead to new developments in the field of current-controlled quantum devices, including everything from sensors to computers to secure communication.
Scientists are looking forward to understanding what makes this material special and which microscopic ingredients are needed for related materials to become useful quantum technologies in the future.