Strange material demonstrates exotic quantum state at room temperature

Many quantum effects can only be produced at extremely cold temperatures, which limits their usefulness in real-world conditions. Today, researchers at Princeton have revealed a strange quantum state occurring in a material at room temperature.

A topological insulator is a material whose structure conducts electrons in a unique way. Most of the material is an insulator, completely preventing the flow of electrons through it. However, the thin layers on its surface and along its edges are highly conductive, allowing electrons to flow freely at high efficiencies. Given these strange properties, topological insulators can host intriguing quantum states that could be useful for building future quantum technologies.

But of course there is a catch: most quantum states are extremely fragile and break down in the face of interference. Heat, or thermal noise, is a major trigger – when materials heat up, the atoms within them vibrate at higher energies, disrupting the quantum state. As such, most experiments and technologies that use quantum effects must be performed at temperatures near absolute zero, where the movements of atoms slow down. But that makes these technologies impractical for wider use.

In the new study, the Princeton researchers found a way around this problem, by observing quantum effects in a topological insulator at room temperature. Their material of choice was an inorganic crystalline compound known as bismuth bromide.

This material was found to have just the right bandgap, an insulating “barrier” where electrons cannot exist with certain energy levels. This forbidden band must be wide enough to protect against thermal noise, but not so wide as to disturb the spin-orbit coupling effect of the electrons, which is essential for their stability. Bismuth bromide was found to have a band gap of over 200 millielectron-volts, just in the “sweet spot” to maintain the stable quantum state at room temperature.

The team confirmed their finding by observing what is called a quantum spin hall edge state, a property unique to these topological systems. The researchers say the breakthrough will be useful for advancing quantum technologies like spintronics, the emerging field that encodes data in the spins of electrons with higher efficiency than current electronics.

“It’s just great that we found them without giant pressure or ultra-high magnetic fields, making the materials more accessible for developing next-generation quantum technology,” said Nana Shumiya, co-first author of the study. “I believe our discovery will significantly advance the quantum frontier.”

The research was published in the journal Natural materials.

Source: Princeton University

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