Scientists Discover a Magnetic Field Driven Transition in Quantum Semiconductor

The Science

Scientists recently discovered that Mn₃Si₂Te₆ changes from an insulator to an electrically conductive metal when exposed to a magnetic field. This manganese-silicon-tellurium material is a semiconductor. Like other materials, its properties are shaped by the quantum realm. How the electrons interact with each other, their surroundings, electric or magnetic fields, and other factors determine properties such as hardness, ductility, strength, and resistivity. Mn₃Si₂Te₆ has magnetic and electrical behaviors not found in normal metals. In particular, applying a magnetic field to the material causes a weak metallic state with trapped electrical changes to form. This study examined the processes that cause this behavior.

The Impact

This research reveals how materials switch from insulators to metals at a microscopic level. The results uncover new quantum states. They also pave the way to the design of materials with exceptional resistance to changing their electrical resistance when exposed to magnetic fields. Materials with that ability have potential uses in technologies like data storage and sensors.

Summary

Researchers recently discovered that the nodal-line semiconductor Mn₃Si₂Te₆ has a field-driven insulator-to-metal transition and associated colossal magnetoresistance. It also shows evidence for a new type of quantum state involving chiral orbital currents. These qualities persist even in the absence of traditional Jahn-Teller distortions and double exchange mechanisms, raising questions about exactly how and why magnetoresistance occurs along with conjecture as to the likely signatures of loop currents.

In this study, researchers measured the infrared response of Mn₃Si₂Te₆ across the magnetic ordering and field-induced insulator-to-metal transitions in order to explore extremely high magnetoresistance in the absence of Jahn-Teller and double exchange interactions. Rather than a traditional metal with screened phonons, the field-driven insulator-to-metal transition leads to a weakly metallic state with localized carriers. The researchers fit the project's spectral data using a percolation model, providing evidence for electronic inhomogeneity and phase separation. Modeling also reveals a frequency-dependent threshold field for carriers contributing to colossal magnetoresistance. The researchers examined this magnetoresistance in terms of polaron formation, chiral orbital currents, and short-range spin fluctuations. These findings enhance the understanding of insulator-to-metal transitions in new settings and open the door to the design of unconventional colossal magnetoresistant materials.

Funding

This research was supported by the Department of Energy (DOE) Office of Science, Basic Energy Science program, by the National Research Foundation of Korea (NRF), the DOE-funded University of Minnesota Center for Quantum Materials, the Gordon and Betty Moore Foundation's EPiQS initiative, and the National Science Foundation. The work at Brookhaven National Laboratory used the Infrared Lab at the National Synchrotron Light Source II, a DOE Office of Science user facility. The research also used the National High Magnetic Field Laboratory supported by the National Science Foundation and the state of Florida.