US researchers discover new quantum state in a quirky material

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A collaboration of physicists working at different institutes in the U.S. have discovered a new quantum state in an alloy made of magnesium, silicon, and tellurium, a press release said. The finding could result in applications in quantum computing, such as building sensors and communication systems.

The alloy is a crystalline structure denoted as Mn3Si2Te6 and consists of octagonal cells placed in a honeycomb-like arrangement when viewed from above. Though, when viewed from the side, it consists of stacked sheets.

Electrons can move around freely inside the structure. However, due to the randomness of the flow, the traveling of electrons is much like that of vehicles in a traffic jam, giving the material the properties of an insulator.

The researchers were interested in studying the alloy due to a property they had noticed earlier. Called magnetoresistance, the material displayed improved conductivity when placed in the presence of a magnetic field.

While this change in nature is not seen for most materials, it has been observed for some before. In the case of this alloy, the magnetoresistance has been dubbed colossal since, in the presence of the magnetic field, it stops behaving like an insulator and acts like a conducting wire instead.

The researchers also found that the colossal magnetoresistance only came into effect when the magnetic field was applied perpendicular to the honeycomb-like surface. While this was not true for magnetoresistance seen in other materials, the researchers needed a new model to explain why this alloy was behaving so.

Bartlomiej Wroblewski/ iStock

Theoretical physicists at Georgia Tech developed a new mathematical model where they found that current flows between magnetic manganese ions were forbidden by symmetry. However, the octahedrally arranged tellurium ions could carry the currents when the magnetic field was applied in a particular way.

Interestingly, the researchers also found that material could switch between being an insulator and a conductor even when an electric current was applied. This transition, though, was not immediate and could take anywhere between seconds to minutes to happen.

The slower switch is something that the researchers are interested in exploiting to develop new applications in current controlled quantum devices, which could be used for a variety of purposes ranging from computing to sensing as well as communication.

Prior to that, researchers still need to understand more about this newly discovered quantum state while also determining which other materials display these properties.

The research findings were published in the journal Nature.

Study abstract:

Colossal magnetoresistance (CMR) is an extraordinary enhancement of the electrical conductivity in the presence of a magnetic field. 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 avoided1,2. Here, we report an exotic quantum state that is driven by ab plane chiral orbital currents (COC) flowing along edges of MnTe6 octahedra. The c axis orbital moments of ab plane COC couple to the ferrimagnetic Mn spins to drastically increase the ab plane conductivity (CMR) when an external magnetic field is aligned along the magnetic hard c axis. Consequently, COC-driven CMR is highly susceptible to small direct currents exceeding a critical threshold, and can induce a time-dependent, bistable switching that mimics a first-order ‘melting transition’ that is a hallmark of the COC state. The demonstrated current-control of COC-enabled CMR offers a new paradigm for quantum technologies.